AMERICAN
JOURNAL
OF
PHYSIOLOG\
Vol. 229, No. 6, December
Prink-d in U.S.A.
1975.
Pentobarbital vascular
and contraction
smooth
BELLA
T. ALTURA
Depurtments
of Anesthesiology
Ihitler.+-,
Bronx
10461,
Downstcrte
Medictrl
Center,
muscle AND
BURTON
M.
und Physiology, and Depurtment Brooklyn,
ALTURA
Albert of J’hysio/ogy,
New
York
portal tone
vein;
vasoactive
agents;
barbiturates;
Einstein
CoUege
State
University
of Medicine of New
of Yeshiva York,
/1203
BURTON M. ALTUKA. Pentobarbital ALTURA, BELLA 'I‘., AND and contraction of vascular smooth muscle. Am. J. Physiol. 229(6) : 1635-l 640. 1975.~This study, with isolated rat aortic strips and portal veins, was undertaken to: I) study the effects, if any, of pentobarbital Na (PTB) (5 x 1 O-” to 2 x 1 Oe3 M) on reactivity to epinephrine, serotonin, and KCl; 2) determine whether certain concentrations of PTB induce direct actions on aortic strips and portal veins; and 3) gain some insight into how these effects are brought about. The results indicate that PTB can: a) inhibit development of spontaneous mechanical activity in these vessels in ‘anesthetic concentrations; b) dose-dependently attenuate contractions induced by epinephrine, serotonin, and KCl; c) cause a noncompetitive type displacement of the doseresponse curves of these vasoactive agents; d) attenuate Ca2+induced contractions of potassium-depolarized aortic strips and portal veins concomitant with a dose-dependent displacement of these dose-response curves to the right; and e) rapidly relax drugas well as Ca2+ -induced contractions of aortas and portal veins. In addition, the data indicate that rat portal venous smooth muscle is more sensitive to the inhibitory actions of PTB than rat aortic smooth muscle. Overall, these data suggest that concentrations of PTB used to induce surgical anesthesia can exert profound depressant effects on at least two different types of vascular smooth muscle that may be related to actions on movement and/or translocation of Ca2+. rat aorta; rat thesia; vascular
of
anes-
ALTHOUGH PENTOBARBITAL SODIUM (PTB) is known to exert effects on the cardiovascular system (see refs. 23, 32, 34), little definitive work has been done in relation to its effects on blood vessels and the available data are controversial. For example, PTB has been reported to increase ( 1 1 ), decrease (21, 28), or not change (31) peripheral vascular resistance. Even direct microscopic observations on the microcirculation have indicated a multiplicity of different reactions with regard to microvascular tone (24, 25). Although many of the preceding studies collectively could be used to suggest that PTB may in part produce peripheral vasodilatation by a direct action on vascular smooth muscle, the studies are indirect and do not eliminate the CNS, metabolic actions, and/or circulating neurohumoral substances. Direct studies on isolated blood vessels, both arterial and venous, may help to clarify and resolve some of the effects
PTB exerts on vascular smooth muscle. With these points in mind, the present studies were undertaken with isolated rat aortic strips and portal veins. METHODS
Thoracic aortas and portal veins were obtained from decapitated male rats (Wistar strain, 275-425 g). Only L male rats were used since sex and estrogenic hormones are known to affect the reactivity of blood vessels to vasoactivc agents (2, 3, 5). The aortas were cut helically into vascular strips (1.3-l .5 mm wide by 25 mm long) and set up isometrically in vitro under a resting tension of 1.5 g, essentially similar to a procedure described previously (4). Ten-millimeter segments of intact portal veins were tied at both ends with sutures and set up isometrically in vitro under a resting tension of 500 mg. Both the aortic strips and the portal vein segments were equilibrated for 2 h in muscle chambers containing Krebs-Ringer bicarbonate solution, the composition of which was (in mM): NaCl, 118; KCl, 4.7; CaC12, 2.5; KHZP04, 1 2; MgS01*7 HZO, 1.2; NaHCOa, 25.0; and glucose, 10.0. The Krebs-Ringer bicarbonate solution was oxygenated continuously with a 95% 02’5% CO2 mixture and kept at 37°C (PI-I 7.4-7.5). The loading tensions were maintained and periodically adjusted throughout the experiments. The incubation media were routinely changed every 10-l 5 min as a prccaution against interfering metabolites (6). Conventional isometric techniques, with Grass FT03C force-displacement strain gauges and either a model 5 Grass Instruments sixchannel recorder or a Beckman Dynograph four-channel recorder, were utilized (6). After a 2-h incubation period, the following different types of experiments were run on the aortic strips and portal veins. I) Certain aortic strips and portal veins were exposed to Krebs-Ringer bicarbonate containing various concentrations of PTB (i.e., 5 X 10-S to 2 X lob3 M) for 5- to 15-min periods to determine whether or not PTB had any effect on base-line tension and/or development of spontaneous mechanical activity; the latter time periods were chosen since systemic administration of PTB to intact rats induces anesthesia within 15 min. 2) In other experiments different aortas and portal veins were exposed to epinephrine (Adrenalin chloride, Parke, Davis & Company), serotonin (serotonin creatinine sulfate, Nutritional Biochemicals Corp.), angiotensin (angiotensin I I amide,
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B. T.
1636 500
500mg 250mg 1 min
lxli+
b
mg
1
F
FIG. 1. Influence of various concentrations ment of spontaneous mechanical activity and lated rat aortic strips. Arrows indicate point exposed to PTB (M concn). Values on left in represent tension. Top two tracings are from 2 tracings are from another preparation. These Fig. 2 are hand copies of original recordings.
250
I 3
mg
250
mgI
1
of PTB on developresting tension in isoat which tissues were this figure and others 1 aortic strip; bottom tracings and those for
t 1x1o-4
1 t
2.5x1o-4 250
mgI
250
mgI
FIG.
velopment vein.
l-lmin
2. Influence of various concentrations of spontaneous mechanical activity
(M) of PTB on dein isolated rat portal
PORTAL
AORTA
1
[]
3% 2.
700
6 ;7i Z F
600
1
(8)
I
I
T
(18)
T
FIG. 3. Different sensitivity of equipotent epinephrine, serotonin, and KCl-induced contractions on rat aortic strips (Ieft panel) and portal veins (right panel) to inhibition by pentobarbital ( X 10D4 M). Numbers in parentheses indicate different number of preparations utilized. Bars represent 1 SE. All experimental mean values (&SE) are significantly different from controls (without PTB) (P < 0.01).
500
t,
Q 400 GIL t g 300
: 2-
ALTURA
VEIN
I
W 2 -
vE
B. M.
CONTROL
(23) ~PTB(x~O-~AA)
800
AND
and potassium chloride, CIBA-GEIGY), (P 0 t assium American Chemical Society certified) before and after exposure of the tissues to different concentrations of PTB (i.e., 5 X 10m5 to 2 X 10s3 M) (1 0-min preincubation period). These latter experiments employed single agonist doses (i.e., submaximal and maximal) as well as complete cumulative dose-response curves. The results are expressed in developed isometric tension (milligrams) and percent maximal agonist-induced contractile responses. 3) In addition, various doses of PTB were added after the establishment of single-dose agonist-induced contractile responses. 4) Paired aortic strips (cut from the same aorta (6)) and paired portal vein segments equilibrated in normal KrebsRinger bicarbonate solution were exposed to two successive supramaximal doses of epinephrine (10 pg/ml each). Upon relaxation of the last contraction, in normal Krebs-Ringer solution, these paired tissues were exposed for 30 min to a Ca2+-free Krebs-Ringer bicarbonate solution followed by exposure to a Ca2-free potassium depolarizing solution for 45 min. This latter solution had 118 mM NaCl isosmotically replaced with KC1 (total K+ = 123.9 mM). Such tissues contract in response to added Ca2+ (7, 22). Cumulative CaClz dose-response curves therefore were obtained on Ca 2+-depleted paired depolarized, aortic strips in the absence or presence of PTB (1 0-min preincubations). These results are expressed in percent maximal epinephrineinduced contractile responses since it has been demonstrated that catecholamines produce the greatest maximal response in rat aorta and portal veins (7, 10). In other experiments, various doses of PTB were added before and after single-dose CaCl2 (1 .O mM)-induced contractions. Where appropriate, the means (&SE) of the responses in control and experimental (with PTB) vascular tissues were compared for statistical significance by means of the Student t test, multiple-range t test, paired t test, or analysis of variance (20). At least six different preparations were utilized for each type of experiment, with the exception of some serotonin single-dose experiments where four different strips were utilized.
mg
250
ALTURA
200 100 0
0
EPINEPHRINE
SEROTONIN
POTASSIUM
1 2.5
EPINEPHRINE
0
POTASSIUM
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PENTOBARBITAL
AND
CONTRACTION
OF
VASCULAR
M:USCLE
1637
100 [ ] PENTOBARBITAL
SODIUM
(xlo-‘M)
90 [ 80
FIG. 4. Influence of PTB (X low4 M) on catecholamine concentration-effect curves in rat aortic strips. Values are means =k 1 SE. At least 6 different strips were utilized for each concentration of PTB. 100% isometric contractile tension = 1,370 & 42 mg. All experimental dose-response curves are significantly different from controls (P < 0.01).
EPINEPHRINE
(Molar
Cone
)
RESULTS
100 [ ] PENTOBARBITAL
Influence of PTB on bas&line tension and spontaneous mechanical activity of rat aortic strips and portal veins. Figures I and 2 show recordings of typical changes in base-line tension and spontaneous mechanical activity in two isolated aortas and one portal vein, before and after the addition of various concentrations of PTB. A concentration of as little as 2.5 X 1O-4 M PTB m h’b’ 1 its the development of spontaneous mechanical activity in rat aortic strips (Fig. l).l Increasing the concentration of PTB to 5 X low4 M not only inhibits the spontaneous mechanical activity more rapidly but also results in a lowering of base-line tension in the rat aortic strips; the greater the concentration of PTB, the more rapidly the inhibition becomes manifest and the more the base-line tension is lowered in rat aorta. Although Fig. 2 demonstrates that development of spontaneous mechanical activity is also inhibited in rat portal venous smooth muscle by PTB, there are some differences from that seen in rat aorta. For example, I) the threshold inhibitory concentration for PTB in rat portal veins is 1 X 10m4 M, but it is 2.5 times higher in rat aorta; and 2) although PTB lowers base-line tension in rat aortic strips (Fig. l), it has no such effect in rat portal veins (Fig. 2). InfZuence of PTB on contractions of rat aortic strips and portal veins induced by single doses of vasoactive agents. Figure 3 indicates that equipotent contractions induced by three vasoactive agents, used on both rat aorta and portal vein, exhibited the following order of sensitivity to inhibition by PTB: KC1 > serotonin > epinephrine. In addition, Fig. 3 indicates that the contraction of venous smooth muscle is more sensitive to the inhibition by PTB than the arterial smooth muscle. Influence of PTB on amine and potassium dose-response curves of rat aortic strips and portal veins. Figures 4 and 5 demonstrate that catecholamine concentration-effect curves on rat aortas and portal veins, in the presence of PTB, are shifted to the right concomitant with a reduction in maxi-~l
l All rat aortic strips do not always exhibit spontaneous mechanical activity when incubated in normal Krebs-Ringer bicarbonate solution (see ref. 9). In these cases, PTB induces a lowering of base-line tension.
SODIUM
(x10-‘MI
90
:
i= 1J
/
1o-7
-
EPINEPHRINE
10-6 (Molar
10-5
Cone
10-4
)
FIG. 5. Influence of PTB (X low4 M) on catecholamine concentration-effect curves in isolated rat portal veins. Values are means =t 1 SE. At least 6 different strips were utilized for each concentration of PTB. 100% isometric contractile tension = 1,622 & 52 mg. ,411 experimental dose-response curves, except for 0.5 X low4 M PTB, are significantly different from controls (P < 0.01).
mum response. These two figures suggest that the portal venous smooth muscle may be more sensitive than aorta to the inhibitory action of PTB. For example, I) although 1 X 10m4 M PTB fails completely to inhibit catecholamincinduced responses on aortic smooth muscle, it depresses the maximum portal venous responses by 35 %I (Fig. 5) ; and 2) 1 X 10e3 M PTB inhibits portal venous catecholamine-induced maximal responses 95 % (Fig. 5), whereas it inhibits similar responses in aortic smooth muscle by only 50 % (Fig. 4). A similar dose-dependent inhibition of contraction by PTB was noted when serotonin and angiotensin were the stimulants. Potassium-induced maximal con tractions of both aortic strips and portal veins are markedly inhibited by PTB (Fig. 6). The venous smooth muscle con-
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (163.015.154.053) on July 29, 2018. Copyright © 1975 American Physiological Society. All rights reserved.
1638
B. T. AORTA
ALTURA
AND
B. M.
ALTURA
PORTAL VEIN [ J PENTOBARBITAL
CO3
NO (X iom4
M) Dl
FIG. 6. Influence of PTB on KC1 concentration-effect curves in rat aortic strips (Zeft panel) and portal veins (right panel). At least 6 different preparations were utilized for each concentration of PTB on each blood vessel type. 100% isometric contractile tension on aorta = 715 * 37 mg. 100% isometric contractile tension on portal vein = 1,270 & 49 mg. All experimentals are different from controls (P < 0.01).
-
I 10-j KCI
(Molar
Cone)
tractions induced by potassium are extemely sensitive to the actions of PTB (e.g., compare relative changes in shift of dose-response curves and maximum tensions for aorta and portal vein, Fig. 6). Efects of PTB on calcium chloride-induced contractions of rat aortic strips andportal veins. The above data seemed to support the idea that anesthetic (hypnotic) as well as anticonvulsive concentrations of PTB might act rather nonspecifically on vascular smooth muscle to inhibit vasoactive substances capable of evoking contraction. In order to gain some insight into a possible mechanism of action we examined the effects of PTB on calcium-induced contractions of potassium-depolarized arteries and veins (see METHODS for procedure). Pentobarbital not only reduced the magnitude of these calcium-induced contractions of depolarized aortic strips (Fig. 7) and portal veins (Fig. 8), but increasing PTB concentration reduced the magnitude of the maximum tension as well. In addition, PTB caused a dose-dependent displacement and “shallowing” of the sigmoid log concentration-effect curves to the right. As in the case of the vasoactive agents, Ca2+- induced contractions of venous smooth muscle were more sensitive to the inhibitory action of PTB than the arterial smooth muscle; a concentration of as little as 5 X 10V5 M PTB induced threshold effects on the venous muscle, whereas threshold effects were not observed on the arterial muscle until 2.5 X low4 M PTB was utilized. In addition, although 5 X 10D4 M PTB comcontractions on the pletely abolished the Ca2+- induced venous muscle, 2 X 1O-3 M was required for such suppression in the aortic strips. Other experiments indicated that aortic strips and portal veins contracted by treatment with the amines, angiotensin, KCl, and CaC12 were dose-dependently relaxed upon the addition of PTB. Both the relaxant and inhibitory actions of PTB are rapidly reversible after washing with normal Krebs-Ringer bicarbonate solution. DISCUSSION
Although a vasodilator action has been noted for anesthetic and hypnotic doses of PTB (11, 14, 18, 24, 25), it
100 [ IPENTOBARBITAL
2 a
80
wp
70-
5
60-
5 ac 8
50 -
SODIUM
(x10-~)
t
U
g
40-
E
20
30--
10-6
10-5
10-4 [co”~,
10-3
10-T
10-l
(Molar Cone )
FIG. 7. Influence of PTB X 10B4 M on CaCl-induced contractions of potassium-depolarized rat aortas (see METHODS). n = 6-10 each. Values are means & 1 SE. Mean 100% isometric response = 1,026 =t 75 mg. All experimental dose-response curves, except for 1 X 10s4 M PTB, are significantly different from controls (P < 0.01).
has not been clear as to how such an effect is brought about. Several different mechanisms have been proposed previously by a number of investigators : e.g., interference with CNS and/or autonomic reflexes as well as metabolic actions (see refs. 1, 23, 32, 33). In addition, it has been assumed by several previous workers (14, 18) that depression of regional organ blood flows during administration of PTB may be due secondarily to drops in systemic arterial The present findings demonstrate that blood pressure. PTB, in concentrations present under surgical anesthesia or anticonvulsive therapy (i.e., 0.5-2.5 X 10B4 M) (17, 27, 35), may contribute to CNS-induced vasodilatation and/or produce dilatation of peripheral blood vessels by at least two different mechanisms: 1) depression of vasomotor tone via an inhibition of development of spontaneous mechanical activity, and 2) depression of vasomotor tone via an inhibition of the constrictor action of endogenous neurohumoral substances that are believed to play roles in maintaining vascular tone (2, 29).
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PENTOBARBITAL
AND
CONTRACTION
OF
VASCULAR
130 [ IPENTCIBARBITAL 120
SODIUM
[a
(~10~~)
:
110
f -
I T 5 + a al c & w -
100
L
90-
5
80.7
2CY 5
70
[13
ou v z I-
6o
i?
50
-
II
/
[251
ka++l, (Molar 8. Influence of PTB of potassium-depolarized rat Values are means rf: 1 SE. + 68 mg. All experimental different from control (P < FIG.
Cone
1639
MUSCLE
)
(X lo-’ M) on C&l-induced contractions portal veins (see METHODS). n = 6 each. Mean 100% isometric response = 1,440 dose-response curves are significantly 0.01).
The net result of the PTB-induced inhibition of vascular tone and/or attenuation of the arterial and venous constrictor action of circulating neurohumoral agents seen in the present study thus could contribute to, or account for, the fall in systemic blood pressure frequently seen in mammals under pentobarbital-induced surgical anesthesia. In addition, if the portal vein may be used as an example of venous smooth muscle, the greater sensitivity of this tissue to PTB compared with aortic tissue may aid in explaining why PTB can compromise the control of the cardiovascular system (23, 25, 34) and exacerbate the effects of circulatory shock (19). Any explanation proposed to account for the above inhibitory effects of PTB on rat aortic and portal venous smooth muscle should take into account the following facts. 1) There are several well-known actions that this substance exerts on cell membranes in general (1, 33, 34). 2) The inhibition is directed against development of spontaneous
mechanical activity and base-line tension (tone), as well as against development of drug-induced contractile tension. 3) The inhibition develops rapidly (i.e., within seconds). 4) The inhibition is nonspecific. 5) It occurs in different types of blood vessels. S) The inhibition is reversed rapidly with washing (i.e., within a few minutes). The fact that PTB dose-dependently inhibits potassiumand calcium chloride-induced contractions of isolated aortic and portal venous smooth muscle suggests that PTB may be acting directly to reduce the availability of calcium ions to the contractile machinery either at and/or beyond the cell membrane. It is known that such potassiumand calcium chloride-induced contractions of vascular smooth muscle are dependent on extracellular calcium ions that presumably pass through the membrane, which becomes highly permeable in the presence of high potassium ion concentrations (16, 22). Additionally, PTB might interfere somewhere with the interactions of Ca*+ with the contractile proteins. Nayler and Szeto (30) have recently demonstrated that PTB can affect calcium uptake and its distribution in mammalian heart muscle. This could aid in explaining why PTB inhibits development of spontaneous mechanical activity in rat aorta and portal vein. It is thought that such spike activity is dependent on influx of extracellular calcium ions (12, 13). Although other vasoactive agents like epinephrine and serotonin may utilize an intracellular and/or tightly bound membrane calcium pool in contraction of vascular muscle (8, 16, 26), PTB could still interfere with mobility of these cellular calcium pools since it has been shown to penetrate both membranes and cells rapidly (33). Since the log dose-response curves for the drug-induced contractions, in the presence of PTB, are shifted to the right (i.e., EDSO’s are increased) concomitant with a reduction in maximum developed tension, it would appear that PTB may be acting both at and beyond the cell membrane as suggested above. The available data for the use of PTB on other cell systems would seem to be in agreement with the latter conclusion (1, 15, 30, 33). We are grateful for the excellent technical assistance provided by Marjorie K. Nicodemus and Jane Hanley. This study was supported by Grant MH 26236 from the National Institute of Mental Health. Some of these results were reported to the American Society for Pharmacology and Experimental Therapeutics, Montreal, August 1974 (Pharmacologist 16 : 301, 1974). Address reprint requests to: B. T. Altura, Dept. of Physiology, Box 31, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, N. Y. 11203. Received
for publication
27 December
1974.
REFERENCES 1. ALPER, M. H., AND W. FLACKE. The peripheral effects of anesthetics. Ann. Rev. Pharmacol. 9: 273-296, 1969. B. M. Chemical and humoral regulation of blood flow 2. ALTURA, through the precapillary sphincter. Microvascular Res. 3 : 361384, 1971. 3. ALTURA, B. M. Sex as a factor influencing the responsiveness of arterioles to catecholamines. European J. Pharmacol. 20 : 26 l-265, 1972. 4. ALTIJRA, B. M. Significance of amino acid residues in position 8 of vasopressin on contraction of rat blood vessels. Proc. Sot. Exptl. Biol. Med. 142: 1104-1110, 1973. 5. ALTURA, B. M. Sex and sex hormones as factors influencing the
responsiveness of arterioles to catecholamines and neurohypophyseal hormones. Microvascular Res. 6 : 117, 1973. ALTURA, B. M., AND B. T. ALTURA. Differential effects of substrate depletion on drug-induced contractions of rabbit aorta. Am. J. Physiol. 2 19: 1698-1705, 1970. ALWRA, B. M., AND B. T. ALTURA. Peripheral vascular actions of glucocorticoids and their relationship to protection in circulatory shock. J. Pharmacol. Exptl. Therap. 190: 300-315, 1974. ALTURA, B. M., AND B. T. ALTURA. Contractile actions of antihistamines on isolated arterial smooth muscle. J. Pharmacol. ExptL Therap. 191: 262-268, 1974.
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1640 B. M., AND B. T. ALTIJRA. Magnesium and contraction smooth muscle. Microvascular Res. 7 : 145-l 55, 1974. ALTIJRA, B. T., B. M. ALTURA, AND S. BAEZ. Reactivity of aorta and portal vein in germfree rats. Blood l%.&s 12: 206-218, 1975. BARLOW, G., AND D. H. KNOTT. Hemodynamic alterations after 30 minutes of pentobarbital anesthesia in dogs. Am. J. Physiol. 207 : 764-766, 1964. BIAMINO, G., AND B. JOHANSSON. Effects of calcium and sodium 011 contracture tension in the smooth muscle of the rat portal vein. Pjuegers Arch. 32 I : 143- 158, 1970. BIAMINO, G., AND P. KRUCKENBERG. Synchronization and conduction of excitation in the rat aorta. Am. J. Physiol. 217: 376382, 1969. BLAKE, W. D. Some effects of pentobarbital anesthesia on renal hemodynamics, water and electrolyte excretion in the dog. Am. J. Physiol. 191 : 393-398, 1957. BLAUSTEIN, M. P. Barbiturates block sodium and potassium conductance increases in voltage-clamped lobster axons. J. Gen. Physiol. 5 1 : 293-307, 1968. BOHR, D. F. Vascular smooth muscle updated. Circulation Res. 32 : 665-672, 1973. BRODIE, B. B., J. J. BURNS, L. C. MARK, P. A. LIEF, E. BERNSTEIN, AND E. M. PAPPER. The fate of pentobarbital in man and dog and a method for its estimation in biological material. J. Pharmacol. Exptl. Therap. 109 : 26-34, 1953. BUNKER, J. P. Splanchnic and renal circulation-effects of anesthetics. In: Effects of Anesthetics on the Circulation, edited by H. L. Price and P. J. Cohen. Springfield, Ill. : Thomas, 1964, p. 244248. CHIEN, S. Hemodynamics in hemorrhage: influences of sympathetic nerves and pentobarbital anesthesia. Proc. Sot. Exptl. Biol. Med. 136: 271-275, 1971. FINNEY, D. J. Statistical Method in Biological Assay (2nd ed.). London: Griffin, 1964, p. 99-l 38. FORSYTH, R. P., AND B. I. HOFFBRAND. Redistribution of cardiac output after sodium pentobarbital anesthesia in the monkey. Am. J. Physiol. 218: 214-217, 1970. GODFRAIND, T., AND A. KABA. Blockade or reversal of the contraction induced by calcium and adrenaline in depolarized arterial smooth muscle. Bit. J. Pharmacol. 36 : 549-560, 1969.
9. ALTURA,
B. T. 23. GREISHEIMER,
of arterial
10. 11.
12.
13.
14.
15.
16. 17.
18.
19.
20. 21.
22.
Handbook
24.
E. M.
ALTURA
AND
B. M.
-4LTURA
The
circulatory effects of anesthetics. In: Washington, DC. : Am. Physiol. 70, p. 2477-2510. AND E. LONGNECKER. Quantitaof microvascular diameters during pentobarbital anesthesia in the bat. Anesthesiology 35: 337-342,
of Physiology.
Circulation. Sot., 1965, sect. 2, vol. III, chapt. HARRIS, P. D., L. F. HODOVAL,
tive analysis and thiopental 1971. 25. HERSHEY, S. G., B. W. ZWEIFACH, AND E. A. ROVENSTINE. Effects of depth of anesthesia on behavior of peripheral vascular bed. Anesthesiology 14 : 245-254, 1953. L., AND A. SURIA. The link between agonist action 26. HURWITZ, and response in smooth muscle. Ann. Rev. Pharmacoi. 11 : 303326, 1971. 27. LARRABEE, M. G., AND J. M. POSTERNAK. Selective action of anesthetics on synapses and axons in mammalian sympathetic ganglia. J. Neurophysiol. 15 : 9 1- 114, 1952. 28. MACCANNELL, K. L. The effects of barbiturates on regional blood flows. Can. Anaesthesiol. Sot. J. 16 : l-6, 1969. 29. MELLANDER, S., AND B. JOHANSSON. Control of resistance, exchange and capacitance functions in the peripheral circulation. Pharmacoi. Rev. 20: 117-196, 1968. 30. NAYLER, W. G., AND J. SZETO. Effect of sodium pentobarbital on calcium in mammalian heart muscle. Am. J. Physiol. 222 : 339-344,
1972.
F., AND I. H. PAGE. Hemodynamic changes in dogs 31. OLMSTEAD, caused by sodium pentobarbital anesthesia. Am. J. Physiof. 210: 8 17-820, 1966. H. L. General anesthesia and circulatory homeostasis. 32. PRICE, Physiol. Rev. 40: 187-Z 18, 1960. P. The membrane actions of anesthetics and tranqui33. SEEMAN, lizers. Pharmacol. Rev. 24: 583-655, 1972. S. K. Hypnotics and sedatives. I. The barbiturates. 34. SHARPLESS, In : The Pharmacological Basis of Therapeutics (4th ed.), edited by L. S. Goodman and A. Gilman. New York: Macmillan, 1970, p. 98-120. E. S., AND G. T. PASANANTI. Utility of clinical chemical 35. VESELL, determinations of drug concentrations in biological fluids. Clin. Chem.
17: 851-866,
1971.
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JOURNAL
OF
PHYSIOLOG\
Vol. 229, No. 6, December
Prink-d in U.S.A.
1975.
Pentobarbital vascular
and contraction
smooth
BELLA
T. ALTURA
Depurtments
of Anesthesiology
Ihitler.+-,
Bronx
10461,
Downstcrte
Medictrl
Center,
muscle AND
BURTON
M.
und Physiology, and Depurtment Brooklyn,
ALTURA
Albert of J’hysio/ogy,
New
York
portal tone
vein;
vasoactive
agents;
barbiturates;
Einstein
CoUege
State
University
of Medicine of New
of Yeshiva York,
/1203
BURTON M. ALTUKA. Pentobarbital ALTURA, BELLA 'I‘., AND and contraction of vascular smooth muscle. Am. J. Physiol. 229(6) : 1635-l 640. 1975.~This study, with isolated rat aortic strips and portal veins, was undertaken to: I) study the effects, if any, of pentobarbital Na (PTB) (5 x 1 O-” to 2 x 1 Oe3 M) on reactivity to epinephrine, serotonin, and KCl; 2) determine whether certain concentrations of PTB induce direct actions on aortic strips and portal veins; and 3) gain some insight into how these effects are brought about. The results indicate that PTB can: a) inhibit development of spontaneous mechanical activity in these vessels in ‘anesthetic concentrations; b) dose-dependently attenuate contractions induced by epinephrine, serotonin, and KCl; c) cause a noncompetitive type displacement of the doseresponse curves of these vasoactive agents; d) attenuate Ca2+induced contractions of potassium-depolarized aortic strips and portal veins concomitant with a dose-dependent displacement of these dose-response curves to the right; and e) rapidly relax drugas well as Ca2+ -induced contractions of aortas and portal veins. In addition, the data indicate that rat portal venous smooth muscle is more sensitive to the inhibitory actions of PTB than rat aortic smooth muscle. Overall, these data suggest that concentrations of PTB used to induce surgical anesthesia can exert profound depressant effects on at least two different types of vascular smooth muscle that may be related to actions on movement and/or translocation of Ca2+. rat aorta; rat thesia; vascular
of
anes-
ALTHOUGH PENTOBARBITAL SODIUM (PTB) is known to exert effects on the cardiovascular system (see refs. 23, 32, 34), little definitive work has been done in relation to its effects on blood vessels and the available data are controversial. For example, PTB has been reported to increase ( 1 1 ), decrease (21, 28), or not change (31) peripheral vascular resistance. Even direct microscopic observations on the microcirculation have indicated a multiplicity of different reactions with regard to microvascular tone (24, 25). Although many of the preceding studies collectively could be used to suggest that PTB may in part produce peripheral vasodilatation by a direct action on vascular smooth muscle, the studies are indirect and do not eliminate the CNS, metabolic actions, and/or circulating neurohumoral substances. Direct studies on isolated blood vessels, both arterial and venous, may help to clarify and resolve some of the effects
PTB exerts on vascular smooth muscle. With these points in mind, the present studies were undertaken with isolated rat aortic strips and portal veins. METHODS
Thoracic aortas and portal veins were obtained from decapitated male rats (Wistar strain, 275-425 g). Only L male rats were used since sex and estrogenic hormones are known to affect the reactivity of blood vessels to vasoactivc agents (2, 3, 5). The aortas were cut helically into vascular strips (1.3-l .5 mm wide by 25 mm long) and set up isometrically in vitro under a resting tension of 1.5 g, essentially similar to a procedure described previously (4). Ten-millimeter segments of intact portal veins were tied at both ends with sutures and set up isometrically in vitro under a resting tension of 500 mg. Both the aortic strips and the portal vein segments were equilibrated for 2 h in muscle chambers containing Krebs-Ringer bicarbonate solution, the composition of which was (in mM): NaCl, 118; KCl, 4.7; CaC12, 2.5; KHZP04, 1 2; MgS01*7 HZO, 1.2; NaHCOa, 25.0; and glucose, 10.0. The Krebs-Ringer bicarbonate solution was oxygenated continuously with a 95% 02’5% CO2 mixture and kept at 37°C (PI-I 7.4-7.5). The loading tensions were maintained and periodically adjusted throughout the experiments. The incubation media were routinely changed every 10-l 5 min as a prccaution against interfering metabolites (6). Conventional isometric techniques, with Grass FT03C force-displacement strain gauges and either a model 5 Grass Instruments sixchannel recorder or a Beckman Dynograph four-channel recorder, were utilized (6). After a 2-h incubation period, the following different types of experiments were run on the aortic strips and portal veins. I) Certain aortic strips and portal veins were exposed to Krebs-Ringer bicarbonate containing various concentrations of PTB (i.e., 5 X 10-S to 2 X lob3 M) for 5- to 15-min periods to determine whether or not PTB had any effect on base-line tension and/or development of spontaneous mechanical activity; the latter time periods were chosen since systemic administration of PTB to intact rats induces anesthesia within 15 min. 2) In other experiments different aortas and portal veins were exposed to epinephrine (Adrenalin chloride, Parke, Davis & Company), serotonin (serotonin creatinine sulfate, Nutritional Biochemicals Corp.), angiotensin (angiotensin I I amide,
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B. T.
1636 500
500mg 250mg 1 min
lxli+
b
mg
1
F
FIG. 1. Influence of various concentrations ment of spontaneous mechanical activity and lated rat aortic strips. Arrows indicate point exposed to PTB (M concn). Values on left in represent tension. Top two tracings are from 2 tracings are from another preparation. These Fig. 2 are hand copies of original recordings.
250
I 3
mg
250
mgI
1
of PTB on developresting tension in isoat which tissues were this figure and others 1 aortic strip; bottom tracings and those for
t 1x1o-4
1 t
2.5x1o-4 250
mgI
250
mgI
FIG.
velopment vein.
l-lmin
2. Influence of various concentrations of spontaneous mechanical activity
(M) of PTB on dein isolated rat portal
PORTAL
AORTA
1
[]
3% 2.
700
6 ;7i Z F
600
1
(8)
I
I
T
(18)
T
FIG. 3. Different sensitivity of equipotent epinephrine, serotonin, and KCl-induced contractions on rat aortic strips (Ieft panel) and portal veins (right panel) to inhibition by pentobarbital ( X 10D4 M). Numbers in parentheses indicate different number of preparations utilized. Bars represent 1 SE. All experimental mean values (&SE) are significantly different from controls (without PTB) (P < 0.01).
500
t,
Q 400 GIL t g 300
: 2-
ALTURA
VEIN
I
W 2 -
vE
B. M.
CONTROL
(23) ~PTB(x~O-~AA)
800
AND
and potassium chloride, CIBA-GEIGY), (P 0 t assium American Chemical Society certified) before and after exposure of the tissues to different concentrations of PTB (i.e., 5 X 10m5 to 2 X 10s3 M) (1 0-min preincubation period). These latter experiments employed single agonist doses (i.e., submaximal and maximal) as well as complete cumulative dose-response curves. The results are expressed in developed isometric tension (milligrams) and percent maximal agonist-induced contractile responses. 3) In addition, various doses of PTB were added after the establishment of single-dose agonist-induced contractile responses. 4) Paired aortic strips (cut from the same aorta (6)) and paired portal vein segments equilibrated in normal KrebsRinger bicarbonate solution were exposed to two successive supramaximal doses of epinephrine (10 pg/ml each). Upon relaxation of the last contraction, in normal Krebs-Ringer solution, these paired tissues were exposed for 30 min to a Ca2+-free Krebs-Ringer bicarbonate solution followed by exposure to a Ca2-free potassium depolarizing solution for 45 min. This latter solution had 118 mM NaCl isosmotically replaced with KC1 (total K+ = 123.9 mM). Such tissues contract in response to added Ca2+ (7, 22). Cumulative CaClz dose-response curves therefore were obtained on Ca 2+-depleted paired depolarized, aortic strips in the absence or presence of PTB (1 0-min preincubations). These results are expressed in percent maximal epinephrineinduced contractile responses since it has been demonstrated that catecholamines produce the greatest maximal response in rat aorta and portal veins (7, 10). In other experiments, various doses of PTB were added before and after single-dose CaCl2 (1 .O mM)-induced contractions. Where appropriate, the means (&SE) of the responses in control and experimental (with PTB) vascular tissues were compared for statistical significance by means of the Student t test, multiple-range t test, paired t test, or analysis of variance (20). At least six different preparations were utilized for each type of experiment, with the exception of some serotonin single-dose experiments where four different strips were utilized.
mg
250
ALTURA
200 100 0
0
EPINEPHRINE
SEROTONIN
POTASSIUM
1 2.5
EPINEPHRINE
0
POTASSIUM
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PENTOBARBITAL
AND
CONTRACTION
OF
VASCULAR
M:USCLE
1637
100 [ ] PENTOBARBITAL
SODIUM
(xlo-‘M)
90 [ 80
FIG. 4. Influence of PTB (X low4 M) on catecholamine concentration-effect curves in rat aortic strips. Values are means =k 1 SE. At least 6 different strips were utilized for each concentration of PTB. 100% isometric contractile tension = 1,370 & 42 mg. All experimental dose-response curves are significantly different from controls (P < 0.01).
EPINEPHRINE
(Molar
Cone
)
RESULTS
100 [ ] PENTOBARBITAL
Influence of PTB on bas&line tension and spontaneous mechanical activity of rat aortic strips and portal veins. Figures I and 2 show recordings of typical changes in base-line tension and spontaneous mechanical activity in two isolated aortas and one portal vein, before and after the addition of various concentrations of PTB. A concentration of as little as 2.5 X 1O-4 M PTB m h’b’ 1 its the development of spontaneous mechanical activity in rat aortic strips (Fig. l).l Increasing the concentration of PTB to 5 X low4 M not only inhibits the spontaneous mechanical activity more rapidly but also results in a lowering of base-line tension in the rat aortic strips; the greater the concentration of PTB, the more rapidly the inhibition becomes manifest and the more the base-line tension is lowered in rat aorta. Although Fig. 2 demonstrates that development of spontaneous mechanical activity is also inhibited in rat portal venous smooth muscle by PTB, there are some differences from that seen in rat aorta. For example, I) the threshold inhibitory concentration for PTB in rat portal veins is 1 X 10m4 M, but it is 2.5 times higher in rat aorta; and 2) although PTB lowers base-line tension in rat aortic strips (Fig. l), it has no such effect in rat portal veins (Fig. 2). InfZuence of PTB on contractions of rat aortic strips and portal veins induced by single doses of vasoactive agents. Figure 3 indicates that equipotent contractions induced by three vasoactive agents, used on both rat aorta and portal vein, exhibited the following order of sensitivity to inhibition by PTB: KC1 > serotonin > epinephrine. In addition, Fig. 3 indicates that the contraction of venous smooth muscle is more sensitive to the inhibition by PTB than the arterial smooth muscle. Influence of PTB on amine and potassium dose-response curves of rat aortic strips and portal veins. Figures 4 and 5 demonstrate that catecholamine concentration-effect curves on rat aortas and portal veins, in the presence of PTB, are shifted to the right concomitant with a reduction in maxi-~l
l All rat aortic strips do not always exhibit spontaneous mechanical activity when incubated in normal Krebs-Ringer bicarbonate solution (see ref. 9). In these cases, PTB induces a lowering of base-line tension.
SODIUM
(x10-‘MI
90
:
i= 1J
/
1o-7
-
EPINEPHRINE
10-6 (Molar
10-5
Cone
10-4
)
FIG. 5. Influence of PTB (X low4 M) on catecholamine concentration-effect curves in isolated rat portal veins. Values are means =t 1 SE. At least 6 different strips were utilized for each concentration of PTB. 100% isometric contractile tension = 1,622 & 52 mg. ,411 experimental dose-response curves, except for 0.5 X low4 M PTB, are significantly different from controls (P < 0.01).
mum response. These two figures suggest that the portal venous smooth muscle may be more sensitive than aorta to the inhibitory action of PTB. For example, I) although 1 X 10m4 M PTB fails completely to inhibit catecholamincinduced responses on aortic smooth muscle, it depresses the maximum portal venous responses by 35 %I (Fig. 5) ; and 2) 1 X 10e3 M PTB inhibits portal venous catecholamine-induced maximal responses 95 % (Fig. 5), whereas it inhibits similar responses in aortic smooth muscle by only 50 % (Fig. 4). A similar dose-dependent inhibition of contraction by PTB was noted when serotonin and angiotensin were the stimulants. Potassium-induced maximal con tractions of both aortic strips and portal veins are markedly inhibited by PTB (Fig. 6). The venous smooth muscle con-
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1638
B. T. AORTA
ALTURA
AND
B. M.
ALTURA
PORTAL VEIN [ J PENTOBARBITAL
CO3
NO (X iom4
M) Dl
FIG. 6. Influence of PTB on KC1 concentration-effect curves in rat aortic strips (Zeft panel) and portal veins (right panel). At least 6 different preparations were utilized for each concentration of PTB on each blood vessel type. 100% isometric contractile tension on aorta = 715 * 37 mg. 100% isometric contractile tension on portal vein = 1,270 & 49 mg. All experimentals are different from controls (P < 0.01).
-
I 10-j KCI
(Molar
Cone)
tractions induced by potassium are extemely sensitive to the actions of PTB (e.g., compare relative changes in shift of dose-response curves and maximum tensions for aorta and portal vein, Fig. 6). Efects of PTB on calcium chloride-induced contractions of rat aortic strips andportal veins. The above data seemed to support the idea that anesthetic (hypnotic) as well as anticonvulsive concentrations of PTB might act rather nonspecifically on vascular smooth muscle to inhibit vasoactive substances capable of evoking contraction. In order to gain some insight into a possible mechanism of action we examined the effects of PTB on calcium-induced contractions of potassium-depolarized arteries and veins (see METHODS for procedure). Pentobarbital not only reduced the magnitude of these calcium-induced contractions of depolarized aortic strips (Fig. 7) and portal veins (Fig. 8), but increasing PTB concentration reduced the magnitude of the maximum tension as well. In addition, PTB caused a dose-dependent displacement and “shallowing” of the sigmoid log concentration-effect curves to the right. As in the case of the vasoactive agents, Ca2+- induced contractions of venous smooth muscle were more sensitive to the inhibitory action of PTB than the arterial smooth muscle; a concentration of as little as 5 X 10V5 M PTB induced threshold effects on the venous muscle, whereas threshold effects were not observed on the arterial muscle until 2.5 X low4 M PTB was utilized. In addition, although 5 X 10D4 M PTB comcontractions on the pletely abolished the Ca2+- induced venous muscle, 2 X 1O-3 M was required for such suppression in the aortic strips. Other experiments indicated that aortic strips and portal veins contracted by treatment with the amines, angiotensin, KCl, and CaC12 were dose-dependently relaxed upon the addition of PTB. Both the relaxant and inhibitory actions of PTB are rapidly reversible after washing with normal Krebs-Ringer bicarbonate solution. DISCUSSION
Although a vasodilator action has been noted for anesthetic and hypnotic doses of PTB (11, 14, 18, 24, 25), it
100 [ IPENTOBARBITAL
2 a
80
wp
70-
5
60-
5 ac 8
50 -
SODIUM
(x10-~)
t
U
g
40-
E
20
30--
10-6
10-5
10-4 [co”~,
10-3
10-T
10-l
(Molar Cone )
FIG. 7. Influence of PTB X 10B4 M on CaCl-induced contractions of potassium-depolarized rat aortas (see METHODS). n = 6-10 each. Values are means & 1 SE. Mean 100% isometric response = 1,026 =t 75 mg. All experimental dose-response curves, except for 1 X 10s4 M PTB, are significantly different from controls (P < 0.01).
has not been clear as to how such an effect is brought about. Several different mechanisms have been proposed previously by a number of investigators : e.g., interference with CNS and/or autonomic reflexes as well as metabolic actions (see refs. 1, 23, 32, 33). In addition, it has been assumed by several previous workers (14, 18) that depression of regional organ blood flows during administration of PTB may be due secondarily to drops in systemic arterial The present findings demonstrate that blood pressure. PTB, in concentrations present under surgical anesthesia or anticonvulsive therapy (i.e., 0.5-2.5 X 10B4 M) (17, 27, 35), may contribute to CNS-induced vasodilatation and/or produce dilatation of peripheral blood vessels by at least two different mechanisms: 1) depression of vasomotor tone via an inhibition of development of spontaneous mechanical activity, and 2) depression of vasomotor tone via an inhibition of the constrictor action of endogenous neurohumoral substances that are believed to play roles in maintaining vascular tone (2, 29).
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PENTOBARBITAL
AND
CONTRACTION
OF
VASCULAR
130 [ IPENTCIBARBITAL 120
SODIUM
[a
(~10~~)
:
110
f -
I T 5 + a al c & w -
100
L
90-
5
80.7
2CY 5
70
[13
ou v z I-
6o
i?
50
-
II
/
[251
ka++l, (Molar 8. Influence of PTB of potassium-depolarized rat Values are means rf: 1 SE. + 68 mg. All experimental different from control (P < FIG.
Cone
1639
MUSCLE
)
(X lo-’ M) on C&l-induced contractions portal veins (see METHODS). n = 6 each. Mean 100% isometric response = 1,440 dose-response curves are significantly 0.01).
The net result of the PTB-induced inhibition of vascular tone and/or attenuation of the arterial and venous constrictor action of circulating neurohumoral agents seen in the present study thus could contribute to, or account for, the fall in systemic blood pressure frequently seen in mammals under pentobarbital-induced surgical anesthesia. In addition, if the portal vein may be used as an example of venous smooth muscle, the greater sensitivity of this tissue to PTB compared with aortic tissue may aid in explaining why PTB can compromise the control of the cardiovascular system (23, 25, 34) and exacerbate the effects of circulatory shock (19). Any explanation proposed to account for the above inhibitory effects of PTB on rat aortic and portal venous smooth muscle should take into account the following facts. 1) There are several well-known actions that this substance exerts on cell membranes in general (1, 33, 34). 2) The inhibition is directed against development of spontaneous
mechanical activity and base-line tension (tone), as well as against development of drug-induced contractile tension. 3) The inhibition develops rapidly (i.e., within seconds). 4) The inhibition is nonspecific. 5) It occurs in different types of blood vessels. S) The inhibition is reversed rapidly with washing (i.e., within a few minutes). The fact that PTB dose-dependently inhibits potassiumand calcium chloride-induced contractions of isolated aortic and portal venous smooth muscle suggests that PTB may be acting directly to reduce the availability of calcium ions to the contractile machinery either at and/or beyond the cell membrane. It is known that such potassiumand calcium chloride-induced contractions of vascular smooth muscle are dependent on extracellular calcium ions that presumably pass through the membrane, which becomes highly permeable in the presence of high potassium ion concentrations (16, 22). Additionally, PTB might interfere somewhere with the interactions of Ca*+ with the contractile proteins. Nayler and Szeto (30) have recently demonstrated that PTB can affect calcium uptake and its distribution in mammalian heart muscle. This could aid in explaining why PTB inhibits development of spontaneous mechanical activity in rat aorta and portal vein. It is thought that such spike activity is dependent on influx of extracellular calcium ions (12, 13). Although other vasoactive agents like epinephrine and serotonin may utilize an intracellular and/or tightly bound membrane calcium pool in contraction of vascular muscle (8, 16, 26), PTB could still interfere with mobility of these cellular calcium pools since it has been shown to penetrate both membranes and cells rapidly (33). Since the log dose-response curves for the drug-induced contractions, in the presence of PTB, are shifted to the right (i.e., EDSO’s are increased) concomitant with a reduction in maximum developed tension, it would appear that PTB may be acting both at and beyond the cell membrane as suggested above. The available data for the use of PTB on other cell systems would seem to be in agreement with the latter conclusion (1, 15, 30, 33). We are grateful for the excellent technical assistance provided by Marjorie K. Nicodemus and Jane Hanley. This study was supported by Grant MH 26236 from the National Institute of Mental Health. Some of these results were reported to the American Society for Pharmacology and Experimental Therapeutics, Montreal, August 1974 (Pharmacologist 16 : 301, 1974). Address reprint requests to: B. T. Altura, Dept. of Physiology, Box 31, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, N. Y. 11203. Received
for publication
27 December
1974.
REFERENCES 1. ALPER, M. H., AND W. FLACKE. The peripheral effects of anesthetics. Ann. Rev. Pharmacol. 9: 273-296, 1969. B. M. Chemical and humoral regulation of blood flow 2. ALTURA, through the precapillary sphincter. Microvascular Res. 3 : 361384, 1971. 3. ALTURA, B. M. Sex as a factor influencing the responsiveness of arterioles to catecholamines. European J. Pharmacol. 20 : 26 l-265, 1972. 4. ALTIJRA, B. M. Significance of amino acid residues in position 8 of vasopressin on contraction of rat blood vessels. Proc. Sot. Exptl. Biol. Med. 142: 1104-1110, 1973. 5. ALTURA, B. M. Sex and sex hormones as factors influencing the
responsiveness of arterioles to catecholamines and neurohypophyseal hormones. Microvascular Res. 6 : 117, 1973. ALTURA, B. M., AND B. T. ALTURA. Differential effects of substrate depletion on drug-induced contractions of rabbit aorta. Am. J. Physiol. 2 19: 1698-1705, 1970. ALWRA, B. M., AND B. T. ALTURA. Peripheral vascular actions of glucocorticoids and their relationship to protection in circulatory shock. J. Pharmacol. Exptl. Therap. 190: 300-315, 1974. ALTURA, B. M., AND B. T. ALTURA. Contractile actions of antihistamines on isolated arterial smooth muscle. J. Pharmacol. ExptL Therap. 191: 262-268, 1974.
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1640 B. M., AND B. T. ALTIJRA. Magnesium and contraction smooth muscle. Microvascular Res. 7 : 145-l 55, 1974. ALTIJRA, B. T., B. M. ALTURA, AND S. BAEZ. Reactivity of aorta and portal vein in germfree rats. Blood l%.&s 12: 206-218, 1975. BARLOW, G., AND D. H. KNOTT. Hemodynamic alterations after 30 minutes of pentobarbital anesthesia in dogs. Am. J. Physiol. 207 : 764-766, 1964. BIAMINO, G., AND B. JOHANSSON. Effects of calcium and sodium 011 contracture tension in the smooth muscle of the rat portal vein. Pjuegers Arch. 32 I : 143- 158, 1970. BIAMINO, G., AND P. KRUCKENBERG. Synchronization and conduction of excitation in the rat aorta. Am. J. Physiol. 217: 376382, 1969. BLAKE, W. D. Some effects of pentobarbital anesthesia on renal hemodynamics, water and electrolyte excretion in the dog. Am. J. Physiol. 191 : 393-398, 1957. BLAUSTEIN, M. P. Barbiturates block sodium and potassium conductance increases in voltage-clamped lobster axons. J. Gen. Physiol. 5 1 : 293-307, 1968. BOHR, D. F. Vascular smooth muscle updated. Circulation Res. 32 : 665-672, 1973. BRODIE, B. B., J. J. BURNS, L. C. MARK, P. A. LIEF, E. BERNSTEIN, AND E. M. PAPPER. The fate of pentobarbital in man and dog and a method for its estimation in biological material. J. Pharmacol. Exptl. Therap. 109 : 26-34, 1953. BUNKER, J. P. Splanchnic and renal circulation-effects of anesthetics. In: Effects of Anesthetics on the Circulation, edited by H. L. Price and P. J. Cohen. Springfield, Ill. : Thomas, 1964, p. 244248. CHIEN, S. Hemodynamics in hemorrhage: influences of sympathetic nerves and pentobarbital anesthesia. Proc. Sot. Exptl. Biol. Med. 136: 271-275, 1971. FINNEY, D. J. Statistical Method in Biological Assay (2nd ed.). London: Griffin, 1964, p. 99-l 38. FORSYTH, R. P., AND B. I. HOFFBRAND. Redistribution of cardiac output after sodium pentobarbital anesthesia in the monkey. Am. J. Physiol. 218: 214-217, 1970. GODFRAIND, T., AND A. KABA. Blockade or reversal of the contraction induced by calcium and adrenaline in depolarized arterial smooth muscle. Bit. J. Pharmacol. 36 : 549-560, 1969.
9. ALTURA,
B. T. 23. GREISHEIMER,
of arterial
10. 11.
12.
13.
14.
15.
16. 17.
18.
19.
20. 21.
22.
Handbook
24.
E. M.
ALTURA
AND
B. M.
-4LTURA
The
circulatory effects of anesthetics. In: Washington, DC. : Am. Physiol. 70, p. 2477-2510. AND E. LONGNECKER. Quantitaof microvascular diameters during pentobarbital anesthesia in the bat. Anesthesiology 35: 337-342,
of Physiology.
Circulation. Sot., 1965, sect. 2, vol. III, chapt. HARRIS, P. D., L. F. HODOVAL,
tive analysis and thiopental 1971. 25. HERSHEY, S. G., B. W. ZWEIFACH, AND E. A. ROVENSTINE. Effects of depth of anesthesia on behavior of peripheral vascular bed. Anesthesiology 14 : 245-254, 1953. L., AND A. SURIA. The link between agonist action 26. HURWITZ, and response in smooth muscle. Ann. Rev. Pharmacoi. 11 : 303326, 1971. 27. LARRABEE, M. G., AND J. M. POSTERNAK. Selective action of anesthetics on synapses and axons in mammalian sympathetic ganglia. J. Neurophysiol. 15 : 9 1- 114, 1952. 28. MACCANNELL, K. L. The effects of barbiturates on regional blood flows. Can. Anaesthesiol. Sot. J. 16 : l-6, 1969. 29. MELLANDER, S., AND B. JOHANSSON. Control of resistance, exchange and capacitance functions in the peripheral circulation. Pharmacoi. Rev. 20: 117-196, 1968. 30. NAYLER, W. G., AND J. SZETO. Effect of sodium pentobarbital on calcium in mammalian heart muscle. Am. J. Physiol. 222 : 339-344,
1972.
F., AND I. H. PAGE. Hemodynamic changes in dogs 31. OLMSTEAD, caused by sodium pentobarbital anesthesia. Am. J. Physiof. 210: 8 17-820, 1966. H. L. General anesthesia and circulatory homeostasis. 32. PRICE, Physiol. Rev. 40: 187-Z 18, 1960. P. The membrane actions of anesthetics and tranqui33. SEEMAN, lizers. Pharmacol. Rev. 24: 583-655, 1972. S. K. Hypnotics and sedatives. I. The barbiturates. 34. SHARPLESS, In : The Pharmacological Basis of Therapeutics (4th ed.), edited by L. S. Goodman and A. Gilman. New York: Macmillan, 1970, p. 98-120. E. S., AND G. T. PASANANTI. Utility of clinical chemical 35. VESELL, determinations of drug concentrations in biological fluids. Clin. Chem.
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1971.
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