Histaminergic pharmacology esophageal sphincter
of primate
F. C. BROWN, A. DUBOIS, AND D. 0. CASTELL Department of Internal Medicine, National Naval Medical University of Health Sciences, Bethesda, Maryland 20014
BROWN, F. C., A. DUBOIS, AND D. 0. CASTELL. Histaminergic pharmacolugy of primate lower esophageal sphincter. Am. J. Physiol. 235(l): E42-E46, 1978 or Am. J. Physiol.: Endocrinol. Metab. Gastrointest. Physiol. 4( 1): E42-E46, 1978. -We have studied the lower esophageal sphincter (LES) response to exogenous histamine and to H,- and Hz-blocking agents in the awake baboon. Increasing intravenous bolus doses of histamine produce an increase in LES pressure with a maximum response at a dose of 12 pg/kg. HI-receptor blockade with chlorpheniramine over a wide dose range did not alter basal LES pressure but did abolish the response of the LES to exogenous histamine. Hz-receptor blockade with cimetidine at doses markedly inhibiting gastric acid secretion (2 mg/kg h) did not alter basal LES pressure or the response of the LES to exogenous histamine. In addition, cimetidine did not alter the response of the LES to pentagastrin and bethanechol. Although histamine and histamine receptors are important in gastric secretion, they appear to have no identifiable role in the maintenance of basal LES smooth muscle tone in the baboon. These results demonstrate the presence of a stimulator-y H, receptor on baboon LES smooth muscle, but provide no evidence for the presence of an &inhibitory receptor. As opposed to the parietal cell, the LES response to pentagastrin and bethanechol does not require a H, receptor. l
histamine; H,- and Hz-receptor blockade; H,- and H,-inhibitory blockade; baboon; cimetidine; pentagastrin; bethanechol
of compounds that block histaminestimulated gastric acid secretion has led to the discovery of two distinct classes of histamine receptors that have been designated as H, and H,. The H, receptors mediate allergic reactions, bronchospasm, uterine contraction, and vascular tone (1, 4). The H, receptor primarily functions in gastric acid secretion in man, but has also been shown to inhibit uterine contraction and to have a chronotropic action on the heart in other species (17). These observations have led to renewed interest in the role of histamine and histamine receptors in gastrointestinal physiology, including smooth muscle function. Because of the ubiquitous distribution of histamine and its importance in gastric acid secretion, the effect of histamine and the H,- and HZ-blocking agents on the motor functions of the gastrointestinal tract is of obvious physiological interest. The lower esophageal sphincter (LES) represents an easily identified region of gastrointestinal smooth muscle, which is readily available for in vivo studies. In addition, because the LES is thought to be important in the prevention of gastroesoTHE DEVELOPMENT
lower
Center and Uniformed
Services
phageal reflux, histamine-related effects on this smooth muscle region should provide information relative to the clinical use of HZ-receptor blocking agents in treatment of disease states characterized by peptic ulceration, including patients with reflux disease. In this study, we report results on in vivo studies of histaminergic pharmacology of the LES. METHODS
Animal model. All studies were performed in awake restrained male baboons (Papio anubis) weighing between 20 and 30 kg. The animals were anesthetized with ketamine (7.5 mg/kg im), placed in restraint chairs, and allowed to awaken for 120 min prior to study to minimize the anesthetic-induced depression of LES tone (3). Intraluminal manometry. LES pressures were measured by a standard intraluminal manometry system (8). The cha racteristics of the system were such that occlusion of the catheter orifices gave a pressure rise rate in excess of 100 mmHg/s. The tubing was passed through the nares into the stomach and slowly withdrawn across the LES until the middle orifice was positioned at the point of maximal sphincter pressure just caudad to the pressure inversion point. The position of the recording apparatus was confirmed at frequent intervals (no greater than every 4 min) by identification of the pressure inversion point. LES pressure was recorded in mmHg at the midinspiratory point with gastric fundal pressure as the zero reference point. Swallowing was monitored by use of an intraesophageal catheter orifice. Pharmacologic studies. Test substances were administered as intravenous bolus doses or as constant infusions. Prior to each pharmacological study, base-line LES pressure was recorded for 30 min, and a mean base-line value was obtained by averaging the mean sphincter pressures for each minute of this period. Drug responses were evaluated by averaging the mean pressure values for each of the five maximum individual 1 min observation periods recorded after injection of the pharmacological agent. Drugs used were histamine phosphate (Lilly), chlorpheniramine maleate (Schering), cimetidine (Smith, Kline & French), pentagastrin (Ayerst) and bethanechol HCl (Merck). All drug dosages are expressed as the base.
E42
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
HISTAMINE
ON
LOWER
ESOPHAGEAL
E43
SPHINCTER
After recording of the basal LES pressure for 30 min, RESULTS the response of the LES smooth muscle to exogenous Histamine phosphate demonstrated a clear dose-rehistamine was studied by the administration of intralated pressor effect on LES smooth muscle. From a venous bolus doses of histamine phosphate diluted in mean basal pressure of 22.1 t 2.1 mmHg t SE, mean sterile water. Doses studied were 0.75, 1.5, 3.0, 6.0, and peak pressures were significantly increased at doses of 12.0 pg/kg, and pressures were recorded for 20 min after 6 pg/kg (41.3 + - 4.3 mmHg; P < 0.05) and 12 pg/kg (51.0 each dose. t 4.4 mmHg, P < 0.01) (Fig. 1). The response of the The effect of HI-receptor blockade on LES pressure sphincter to exogenous histamine at all doses studied was evaluated by use of chlorpheniramine maleate, a occurred within 3 min and had a mean duration of 12 pure H,-blocking agent chosen because it is relatively min. Doses above this level produced such pronounced free of the atropine effect of many H,-blocking agents side effects on animal movement and swallowing that (16). After th e base-line recording, intravenous bolus accurate measurement of LES pressure was not possidoses of 10, 20, 40, 80, and 160 pg/kg were injected, and ble pressure was recorded for 30 min afier each dose. I&receptor blockade with a wide range of doses of Hz-receptor blockade was studied by constant intrachlorpheniramine did not alter the basal tone of the venous infusion of cimetidine in dosesof 1 mg/kg h and LES. The mean sphincter pressures for 30 min after all 2 h, each for a minimum of 2 h after a 30-min doses of chlorpheniramine did not differ significantly bas&line recording. Prior studies in the same animals from the mean basal pressure of 26,6 t 2.8 mmHg or indicated that these dosesof cimetidine produce, respec- from each other. tively, a 50 and 85% suppression of maximally stimuHz-receptor blockade produced by the constant infulated gastric hydrogen ion secretion (pentagastrin 6 pg/ sion of cimetidine resulted in significant (P < 0.01) kg’ h). For these studies, gastric acid secretion was suppression of pentagastrin-stimulated gastric acid seevaluated using a dye dilution method that measures cretion in the baboon. The 1 mg/kg h dose produced a hydrogen ion and water secretion as well as the rate of mean decrease of 50 2 6.4% in maximal stimulated gastric emptying (9). Cimetidine blood levels were mea- gastric acid secretion. The 2 mg/kg h dose reduced acid sured by Smith, Kline & French Laboratory (14). secretion by a mean value of 85 t 8.8%. In addition, the The combined effect of H,- and Hz-receptor blockade cimetidine blood level of 1.07 pg/ml obtained during the was evaluated by recording LES pressure for 2 h after 2 mg/kg h infusion rate is in the appropriate therapeuadministration of chlorpheniramine (40 pg/kg) and ci- tic range for suppression of acid secretion (2). metidine (2 mg/kg h). Cimetidine infusions of I and 2 h did not alter The response of the LES to exogenous histamine basal LES tone. The mean pressures of 19.8 t 3.5 during H, blockade with chlorpheniramine (40 pg/kg) mmHg at an infusion rate of 1 mg/kg h and 24.1 -+ 3.4 was determined by the injection of intravenous bolus mmHg at 2 mg/kg h did not differ significantly from doses of histamine phosphate identical to those used to the mean basal value of 24.0 ? 2.6 mmHg or from each determine the histamine dose-response curve described other, above. AfZer the chlorpheniramine injection, base-line In addition, the combination of H, blockade with LES pressure was recorded for 15 min prior to histamine chlorpheniramine (40 pg/kg) and H, blockade with injections. cimetidine (2 mg/kg h) produced a mean sphincter Evaluation of Hz-receptor blockade on the response of pressure of 25.7 * 5.3 mmHg that did not differ signifithe sphincter to histamine was studied in a similar cantly from the basal value of 26.6 5 2.7 mmHg. manner. Cimetidine was infused at a constant rate of 2 The results of HI-receptor blockade with chlorphenimg/kg h for 1 h preceding and during the construction ramine (40 pg/kg) on the response of the LES to of the histamine dose-response curves, and LES pres- intravenous bolus doses of histamine phosphate are sure was monitored constantly throughout the studies. shown in Fig. 2. The mean LES pressures of 29.0 t 4.3 The response of the LES to exogenous bolus doses of pentagastrin was studied by the construction of dose/-t response curves to doses of 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 00# pg/kg. These curves were reconstructed after H, blockade with chlorphenirami ne (40 pgkg) and during H, ‘r blockade with cimetidine (1 and 2 mglkg =h) in a manner analogous to that described above for histamine. Similarily, the interaction between histamine receptors and cholinergic stimulation of the LES was evaluated by the construction of dose-response curves to intravenous bethanechol in increasing bolus dose of 3, 6,12, 25, 50, and 100 pg/kg in the basal state, during H, blockade with chlorpheniramine (40 pg/kg), and during BASAL .75 1.5 3.0 6.0 12.0 Hz-receptor blockade with cimetidine infusions of 1 and IV HISTAMINE @gin/Kg] 2 mg/kg h. FIG. 1. LES pressures basally and after increasing doses of intraStatistical evaluation of the data was accomplished venous histamine phosphate. On this and subsequent figures, open by the application of a three-factor analysis of variance circles represent mean pressure values and vertical lines indicate * 1 SE. with repeated measures and multiple t test (12). l
mg/kg
l
l
l
l
l
mg/kg
l
l
l
l
l
50I
oL------
l
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
# I / / I / /# I0 0/I 4 I-w
E44
M-
HISTAMINE
tt
BROWN,
BASAL .75
AND
CASTELL
The effect of HI-receptor blockade with chlorpheniramine (40 Fg/kg) on the LES response to increasing intravenous bolus doses of bethanechol is shown in Fig. 6. The sphincter pressure response to bethanechol alone is presented for comparison and does not differ from the curve constructed during H, blockade.
&
PENTAGASTRIN
CHLORPHENlRAMlNE IN lw/Kg IV1
L------
DUBOIS,
1
&
4
CHLORPHENlRAMINE-Y?\
/ 1.5
IV HISTAMINE
3.0
6.0
12.0
bgm/Kg)
FIG. 2. LES pressures basally and after increasing doses of intravenous histamine phosphate alone (open circles and broken line) and with chlorpheniramine 40 pg/kg (X’S and solid line).
01
BASAL0.2 FIG.
tagastrin ramine
CMETUME Pmg/Kg* hrl .i5
1.s 3.0 6iI Iv HISTAMINE bnt/Kg]
120
FIG. 3. LES pressures basally and after increasing doses of histamine phosphate alone (open circles and broken line) and with cimetidine 2 mg/kg. hr (X’S and solid line).
mmHg at the 3.0 pg/kg dose, 29.0 t 2.1 mmHg at the 6.0 pg/kg dose, and 31.0 t 4.8 mmHg at the 12.0 pg/kg dose afier chlorpheniramine differ significantly (P < 0;Ol) from the mean values of 37.0 t 4.3 mmHg at 3.0 pg/kg 41.3 -t- 4.3 mmHg at 5.0 pg/kg, and 51.0 t 5.5 mmHi at 12.0 pg/kg recorded during treatment with histamine alone. In addition, mean pressures after all doses of histamine combined with HI-receptor blockade were not significantly different from the mean basal pressure of 26.6 t 2.8 mmHg with chlorpheniramine alone, prior to histamine injections. The histamine dose-response curve and that constructed during cimetidine infusion at a rate of 2 mg/ kg, h are shown in Figure 3. There is no significant difference between the two curves in mean LES pressure at any dose. Dose-response curves of LES pressure to intravenous bolus doses of pentagastrin alone and combined with HI-receptor blockade produced by chlorpheniramine (40 pg/kg) are shown in Figure 4 and are identical. The effect of Hz-receptor blockade with cimetidine (1 and 2 mg/kg h) on the LES response to pentagastrin is summarized in Figure 5. The resulting curves are identical. l
4.
LES pressures basally and after increasing doses of penalone (open circles and broken line) and with chlorpheni40 pg/kg (X’S and solid line).
4
HISTAMINE&
6iSAl
0.4 0.8 1.6 3.2 IV PENTAGASTRIN fjigm/Kg)
=3 s =gf 20 4 4 10 1
0,
CMETlllSE *----II
I2 mm1
T
BASAL0.1
0.2 0.4 0.8 1.6 3.2 IV PENTAGASTRIN (lgmlkg)
6.4
FIG. 5. LES pressures basally and after increasing doses of pentagastrin alone (open circles and broken line), with cimetidine 1 mgl kg* h (filled circles and solid line), and with cimetidine 2 mg/kg 4h (x’s and broken line).
G 80 z 70 -E 60 I
BETHANECHOL
-A BETHANECHOL & CHLORPHENIRAM
I40 mVKg1
I
v
T
w
w
BASAL 3
6
12
25
IV BETHANECHOL
1 50
T 100
[~gm,'Kg]
FIG. 6. LES pressures basally and after increasing doses of bethanechol alone (open circles and broken line) and with chlorpheniramine 40 pg/kg (X'S and solid line).
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
HISTAMINE
ON
LOWIXR
01 BASAL -
3
ESOPHAGEAL
6
12
E45
SPHINCTER
25
50
100
IV BETHANECHOL 1pgm/kg] FIG. 7. thanechol mglkg mh kg, h (.x’s
LES pressures basally and after increasing doses of bealone (open circles and broken line), with cimetidine 1 (filled circles and solid line), and with cimetidine 2 mg/ and solid line).
The interaction between HZ-receptor blockade with constant infusion of cimetidine (1 and 2 mg/kg h) and cholinergic stimulation of the LES with intravenous bolus doses of bethanechol is shown in Figure 7. There is no significant difference between the mean sphincteric pressures to increasing doses of bethanechol alone and those obtained with the combination of bethanechol and cimetidine at infusion rates of 1 and 2 h. l
mg/kg
l
DISCUSSION
The role of histamine in gastrointestinal physiology has been largely centered around gastric secretion with little emphasis on motor effects. The role of histamine and histamine-receptor blockade on the basal, pentagastrin-stimulated, and bethanechol-sti mulated LES was evaluated in the awake baboon, The baboon was chosen for study because of the striking anatomical and physiological similarity to man (3). In addition, the use of an awake, nonanesthetized model has di stinct advantages over previous models in that the sphincter-depressing effect of the anesthetic agents and the variation in depth of anesthesia is avoided (3, 11). The results of our study demonstrate that histamine does have a dose-related pressor effect on the LES smooth muscle and confirm previous in vitro observations of histamine stimulation of the LES in the opossum (7, 15) and of betazole stimulation of the human LES (5). Our study indicates, however, that histamine role in the mai ntedoes not appear to play a significant nance of resting I ,ES tone in the primate because H 1’
receptor blockade with chlorpheniramine, HZ-receptor blockade with cimetidine, and combined histamine-receptor blockade with both agents simultaneously did not alter basal LES pressure. This finding is consistent with recent in vivo studies in man in which no change in resting sphincter pressure was observed after Hzreceptor blockade with various oral doses of cimetidine W) Further, our observations indicate that the stimulatory histamine receptor on the LES smooth muscle of the baboon is of the H, class because this pressor response was blocked by chlorpheniramine, but not by cimetidine. The presence of a stimulatory H, receptor and of an inhibitory H, receptor on the LES has been suggested from in vitro and in vivo studies in the opossum (6). Our data does not support the presence of the postulated HZ-inhibitory receptor in the baboon because cimetidine infusion did not alter basal sphincter pressure or the LES response to exogenous histamine. To further evaluate a possible inhibitory H, receptor and to further clarify histaminergic pharmacology of the LES, dose-response curves were constructed to two agonists for LES contraction: pentagastrin, a gastrointestinal hormone fragment known to cause LES contraction (5) and bethanechol, an analogue of acetylcholine that produces direct muscarinic stimulation of the LES (17). Both pentagastrin and bethanechol produced the expected dose-related pressor responses of the LES muscle. Blockade of either the H, or H, receptors did not alter the response of the LES to pentagastrin or bethanechol, indicating that these two agents act independently of histamine receptors. The lack of modification of pentagastrin stimula tion of the LES by cimeti(15). dine is consistent with other observations One explanation for the divergence of our findings and those found in studies on the opossum (6) may be due to species variation. An alternate explanation may be due tO the use of meti amide rather tha n cimetid ine. for the variance between the We have no explanation two recent studies using the same animal model (opossum) and HZ-blocking agent (metiamide). Because HZ-receptor blockade did not alter the LES pressure or its response to hormonal and cholinergic stimuli, these drugs may be beneficial in the treatment of gastroesophageal reflux as well as other diseases characterized by peptic ulceration. Received
6 O&ber
1977; accepted
in fmal
form
20 February
1978.
REFERENCES 1. BEAVEN, M. A. Histamine. N. Engl. J. Med. 294: 30-36,320-325, 1976. 2. BRIMBLECOMBE, R. W. The pharmacology of cimetidine, a new Hz receptor antagonist. Brit. J. PharmacoL. 53: 435-436, 1975. 3* BROWN, F. C,, R. M. GIDEQN, F. M. VOELKER, AND D. 0. CASTELL. Muscle structure and function of the primate esophagus. Am. J. Vet. Res. In press. 4. BROWNLEE, G., AND I, HARRY, Some pharmacological properties of the circular and longitudinal muscle strips from the guineapig isolated ileum. hit. J. Pharmacol. 21: 544-554, 1963. 5. CASTELL, D. O., AND L. D. HARRIS. Hormonal control of gastroe-
6. 7.
8. 9.
sophageal sphincter strength. N. EngL. J. Med. 282: 866-880, 1970. COHEN, S., AND W. SNAPE. Action of metiamide on the lower esophageal sphincter. Gastroenterology 69: 911-919, 1975. DE CARLE, D. J., M. J. BRODY, AND J. P. CHRISTENSEN. Histamine receptors in the esophageal smooth muscle of the opossum. Gastroenterology 70: 1071-1075, 1976. DODDS, W. J. Instrumentation and methods for intraluminal esophageal manometry. Arch. Internal Med. 136: 515-523, 1976, DUBOIS, A., P. VAN EERDEWEGH, AND J. D. GARDNER. Gastric emptying and secretion in Zollinger-Ellison syndrome. J. Clin.
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
E46
BROWN,
Invest. 59: 255-263, 1977. 10. FREELAND, G. R., R. H. HIGGS, AND D. 0. CASTELL. The effect of cimetidine on the lower esophageal sphincter in normal subjects. CZin. Res. 24: 284A, 1976. 11. HALL, A. W., A. R. MOSSA, J. CLARK, AND D. SKINNER. The effects of premeditation drugs on the lower esophageal high pressure zone and reflux status of Rhesus monkeys and man. Gut 16: 347-352, 1975. 12. KIRK, R. E. Experimentul Design: Procedures for the Behavioral Sciences. Belmont, Calif: Brooks and Cole, 1968, vol. 1, p. 283. 13. KONTUREK, S. J., T. DEMITRESCU, AND T. RADECK. The role of histamine receptors in the stimulation of gastric acid secretion. Am. J. Digest. Diseases 19: 999-1006, 1974. 14. RANDOLF, W. C., V. L. OSBORNE, S. S. WALKENSTEIN, AND A. P. INTOCCIA. High-pressure liquid chromatographic analysis of
15.
16.
17.
18.
DUBOIS,
AND
CASTELL
cimetidine, a histamine HZ-receptor antagonist, in blood and urine. J. PharmacoL. Sci. 66: 1148-1158, 1977. RATTAN, S., D. COLN, AND R. K. GOYAL. The mechanisms of action of gastrin on the lower esophageal sphincter. Gastroenterology 70: 828-835, 1976. R~CHA e SILVA, M. Histamine and antihistamines. Handbook of Experimental Pharmncology. New York: Springer-Verlag, 1966, vol. 18. RULING, G. T., R. L. FARRELL, AND D. 0. CA~TELL. Cholinergic responses of the lower esophageal sphincter. Am. J. Physiol. 222: 967-972, 1972. WOOD, C. J., AND M. A. SIMKINS (eds). International Symposium on Histamine H2 Receptor Antagonists. London: Smith, Kline & French, 1973.
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
of primate
F. C. BROWN, A. DUBOIS, AND D. 0. CASTELL Department of Internal Medicine, National Naval Medical University of Health Sciences, Bethesda, Maryland 20014
BROWN, F. C., A. DUBOIS, AND D. 0. CASTELL. Histaminergic pharmacolugy of primate lower esophageal sphincter. Am. J. Physiol. 235(l): E42-E46, 1978 or Am. J. Physiol.: Endocrinol. Metab. Gastrointest. Physiol. 4( 1): E42-E46, 1978. -We have studied the lower esophageal sphincter (LES) response to exogenous histamine and to H,- and Hz-blocking agents in the awake baboon. Increasing intravenous bolus doses of histamine produce an increase in LES pressure with a maximum response at a dose of 12 pg/kg. HI-receptor blockade with chlorpheniramine over a wide dose range did not alter basal LES pressure but did abolish the response of the LES to exogenous histamine. Hz-receptor blockade with cimetidine at doses markedly inhibiting gastric acid secretion (2 mg/kg h) did not alter basal LES pressure or the response of the LES to exogenous histamine. In addition, cimetidine did not alter the response of the LES to pentagastrin and bethanechol. Although histamine and histamine receptors are important in gastric secretion, they appear to have no identifiable role in the maintenance of basal LES smooth muscle tone in the baboon. These results demonstrate the presence of a stimulator-y H, receptor on baboon LES smooth muscle, but provide no evidence for the presence of an &inhibitory receptor. As opposed to the parietal cell, the LES response to pentagastrin and bethanechol does not require a H, receptor. l
histamine; H,- and Hz-receptor blockade; H,- and H,-inhibitory blockade; baboon; cimetidine; pentagastrin; bethanechol
of compounds that block histaminestimulated gastric acid secretion has led to the discovery of two distinct classes of histamine receptors that have been designated as H, and H,. The H, receptors mediate allergic reactions, bronchospasm, uterine contraction, and vascular tone (1, 4). The H, receptor primarily functions in gastric acid secretion in man, but has also been shown to inhibit uterine contraction and to have a chronotropic action on the heart in other species (17). These observations have led to renewed interest in the role of histamine and histamine receptors in gastrointestinal physiology, including smooth muscle function. Because of the ubiquitous distribution of histamine and its importance in gastric acid secretion, the effect of histamine and the H,- and HZ-blocking agents on the motor functions of the gastrointestinal tract is of obvious physiological interest. The lower esophageal sphincter (LES) represents an easily identified region of gastrointestinal smooth muscle, which is readily available for in vivo studies. In addition, because the LES is thought to be important in the prevention of gastroesoTHE DEVELOPMENT
lower
Center and Uniformed
Services
phageal reflux, histamine-related effects on this smooth muscle region should provide information relative to the clinical use of HZ-receptor blocking agents in treatment of disease states characterized by peptic ulceration, including patients with reflux disease. In this study, we report results on in vivo studies of histaminergic pharmacology of the LES. METHODS
Animal model. All studies were performed in awake restrained male baboons (Papio anubis) weighing between 20 and 30 kg. The animals were anesthetized with ketamine (7.5 mg/kg im), placed in restraint chairs, and allowed to awaken for 120 min prior to study to minimize the anesthetic-induced depression of LES tone (3). Intraluminal manometry. LES pressures were measured by a standard intraluminal manometry system (8). The cha racteristics of the system were such that occlusion of the catheter orifices gave a pressure rise rate in excess of 100 mmHg/s. The tubing was passed through the nares into the stomach and slowly withdrawn across the LES until the middle orifice was positioned at the point of maximal sphincter pressure just caudad to the pressure inversion point. The position of the recording apparatus was confirmed at frequent intervals (no greater than every 4 min) by identification of the pressure inversion point. LES pressure was recorded in mmHg at the midinspiratory point with gastric fundal pressure as the zero reference point. Swallowing was monitored by use of an intraesophageal catheter orifice. Pharmacologic studies. Test substances were administered as intravenous bolus doses or as constant infusions. Prior to each pharmacological study, base-line LES pressure was recorded for 30 min, and a mean base-line value was obtained by averaging the mean sphincter pressures for each minute of this period. Drug responses were evaluated by averaging the mean pressure values for each of the five maximum individual 1 min observation periods recorded after injection of the pharmacological agent. Drugs used were histamine phosphate (Lilly), chlorpheniramine maleate (Schering), cimetidine (Smith, Kline & French), pentagastrin (Ayerst) and bethanechol HCl (Merck). All drug dosages are expressed as the base.
E42
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
HISTAMINE
ON
LOWER
ESOPHAGEAL
E43
SPHINCTER
After recording of the basal LES pressure for 30 min, RESULTS the response of the LES smooth muscle to exogenous Histamine phosphate demonstrated a clear dose-rehistamine was studied by the administration of intralated pressor effect on LES smooth muscle. From a venous bolus doses of histamine phosphate diluted in mean basal pressure of 22.1 t 2.1 mmHg t SE, mean sterile water. Doses studied were 0.75, 1.5, 3.0, 6.0, and peak pressures were significantly increased at doses of 12.0 pg/kg, and pressures were recorded for 20 min after 6 pg/kg (41.3 + - 4.3 mmHg; P < 0.05) and 12 pg/kg (51.0 each dose. t 4.4 mmHg, P < 0.01) (Fig. 1). The response of the The effect of HI-receptor blockade on LES pressure sphincter to exogenous histamine at all doses studied was evaluated by use of chlorpheniramine maleate, a occurred within 3 min and had a mean duration of 12 pure H,-blocking agent chosen because it is relatively min. Doses above this level produced such pronounced free of the atropine effect of many H,-blocking agents side effects on animal movement and swallowing that (16). After th e base-line recording, intravenous bolus accurate measurement of LES pressure was not possidoses of 10, 20, 40, 80, and 160 pg/kg were injected, and ble pressure was recorded for 30 min afier each dose. I&receptor blockade with a wide range of doses of Hz-receptor blockade was studied by constant intrachlorpheniramine did not alter the basal tone of the venous infusion of cimetidine in dosesof 1 mg/kg h and LES. The mean sphincter pressures for 30 min after all 2 h, each for a minimum of 2 h after a 30-min doses of chlorpheniramine did not differ significantly bas&line recording. Prior studies in the same animals from the mean basal pressure of 26,6 t 2.8 mmHg or indicated that these dosesof cimetidine produce, respec- from each other. tively, a 50 and 85% suppression of maximally stimuHz-receptor blockade produced by the constant infulated gastric hydrogen ion secretion (pentagastrin 6 pg/ sion of cimetidine resulted in significant (P < 0.01) kg’ h). For these studies, gastric acid secretion was suppression of pentagastrin-stimulated gastric acid seevaluated using a dye dilution method that measures cretion in the baboon. The 1 mg/kg h dose produced a hydrogen ion and water secretion as well as the rate of mean decrease of 50 2 6.4% in maximal stimulated gastric emptying (9). Cimetidine blood levels were mea- gastric acid secretion. The 2 mg/kg h dose reduced acid sured by Smith, Kline & French Laboratory (14). secretion by a mean value of 85 t 8.8%. In addition, the The combined effect of H,- and Hz-receptor blockade cimetidine blood level of 1.07 pg/ml obtained during the was evaluated by recording LES pressure for 2 h after 2 mg/kg h infusion rate is in the appropriate therapeuadministration of chlorpheniramine (40 pg/kg) and ci- tic range for suppression of acid secretion (2). metidine (2 mg/kg h). Cimetidine infusions of I and 2 h did not alter The response of the LES to exogenous histamine basal LES tone. The mean pressures of 19.8 t 3.5 during H, blockade with chlorpheniramine (40 pg/kg) mmHg at an infusion rate of 1 mg/kg h and 24.1 -+ 3.4 was determined by the injection of intravenous bolus mmHg at 2 mg/kg h did not differ significantly from doses of histamine phosphate identical to those used to the mean basal value of 24.0 ? 2.6 mmHg or from each determine the histamine dose-response curve described other, above. AfZer the chlorpheniramine injection, base-line In addition, the combination of H, blockade with LES pressure was recorded for 15 min prior to histamine chlorpheniramine (40 pg/kg) and H, blockade with injections. cimetidine (2 mg/kg h) produced a mean sphincter Evaluation of Hz-receptor blockade on the response of pressure of 25.7 * 5.3 mmHg that did not differ signifithe sphincter to histamine was studied in a similar cantly from the basal value of 26.6 5 2.7 mmHg. manner. Cimetidine was infused at a constant rate of 2 The results of HI-receptor blockade with chlorphenimg/kg h for 1 h preceding and during the construction ramine (40 pg/kg) on the response of the LES to of the histamine dose-response curves, and LES pres- intravenous bolus doses of histamine phosphate are sure was monitored constantly throughout the studies. shown in Fig. 2. The mean LES pressures of 29.0 t 4.3 The response of the LES to exogenous bolus doses of pentagastrin was studied by the construction of dose/-t response curves to doses of 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 00# pg/kg. These curves were reconstructed after H, blockade with chlorphenirami ne (40 pgkg) and during H, ‘r blockade with cimetidine (1 and 2 mglkg =h) in a manner analogous to that described above for histamine. Similarily, the interaction between histamine receptors and cholinergic stimulation of the LES was evaluated by the construction of dose-response curves to intravenous bethanechol in increasing bolus dose of 3, 6,12, 25, 50, and 100 pg/kg in the basal state, during H, blockade with chlorpheniramine (40 pg/kg), and during BASAL .75 1.5 3.0 6.0 12.0 Hz-receptor blockade with cimetidine infusions of 1 and IV HISTAMINE @gin/Kg] 2 mg/kg h. FIG. 1. LES pressures basally and after increasing doses of intraStatistical evaluation of the data was accomplished venous histamine phosphate. On this and subsequent figures, open by the application of a three-factor analysis of variance circles represent mean pressure values and vertical lines indicate * 1 SE. with repeated measures and multiple t test (12). l
mg/kg
l
l
l
l
l
mg/kg
l
l
l
l
l
50I
oL------
l
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
# I / / I / /# I0 0/I 4 I-w
E44
M-
HISTAMINE
tt
BROWN,
BASAL .75
AND
CASTELL
The effect of HI-receptor blockade with chlorpheniramine (40 Fg/kg) on the LES response to increasing intravenous bolus doses of bethanechol is shown in Fig. 6. The sphincter pressure response to bethanechol alone is presented for comparison and does not differ from the curve constructed during H, blockade.
&
PENTAGASTRIN
CHLORPHENlRAMlNE IN lw/Kg IV1
L------
DUBOIS,
1
&
4
CHLORPHENlRAMINE-Y?\
/ 1.5
IV HISTAMINE
3.0
6.0
12.0
bgm/Kg)
FIG. 2. LES pressures basally and after increasing doses of intravenous histamine phosphate alone (open circles and broken line) and with chlorpheniramine 40 pg/kg (X’S and solid line).
01
BASAL0.2 FIG.
tagastrin ramine
CMETUME Pmg/Kg* hrl .i5
1.s 3.0 6iI Iv HISTAMINE bnt/Kg]
120
FIG. 3. LES pressures basally and after increasing doses of histamine phosphate alone (open circles and broken line) and with cimetidine 2 mg/kg. hr (X’S and solid line).
mmHg at the 3.0 pg/kg dose, 29.0 t 2.1 mmHg at the 6.0 pg/kg dose, and 31.0 t 4.8 mmHg at the 12.0 pg/kg dose afier chlorpheniramine differ significantly (P < 0;Ol) from the mean values of 37.0 t 4.3 mmHg at 3.0 pg/kg 41.3 -t- 4.3 mmHg at 5.0 pg/kg, and 51.0 t 5.5 mmHi at 12.0 pg/kg recorded during treatment with histamine alone. In addition, mean pressures after all doses of histamine combined with HI-receptor blockade were not significantly different from the mean basal pressure of 26.6 t 2.8 mmHg with chlorpheniramine alone, prior to histamine injections. The histamine dose-response curve and that constructed during cimetidine infusion at a rate of 2 mg/ kg, h are shown in Figure 3. There is no significant difference between the two curves in mean LES pressure at any dose. Dose-response curves of LES pressure to intravenous bolus doses of pentagastrin alone and combined with HI-receptor blockade produced by chlorpheniramine (40 pg/kg) are shown in Figure 4 and are identical. The effect of Hz-receptor blockade with cimetidine (1 and 2 mg/kg h) on the LES response to pentagastrin is summarized in Figure 5. The resulting curves are identical. l
4.
LES pressures basally and after increasing doses of penalone (open circles and broken line) and with chlorpheni40 pg/kg (X’S and solid line).
4
HISTAMINE&
6iSAl
0.4 0.8 1.6 3.2 IV PENTAGASTRIN fjigm/Kg)
=3 s =gf 20 4 4 10 1
0,
CMETlllSE *----II
I2 mm1
T
BASAL0.1
0.2 0.4 0.8 1.6 3.2 IV PENTAGASTRIN (lgmlkg)
6.4
FIG. 5. LES pressures basally and after increasing doses of pentagastrin alone (open circles and broken line), with cimetidine 1 mgl kg* h (filled circles and solid line), and with cimetidine 2 mg/kg 4h (x’s and broken line).
G 80 z 70 -E 60 I
BETHANECHOL
-A BETHANECHOL & CHLORPHENIRAM
I40 mVKg1
I
v
T
w
w
BASAL 3
6
12
25
IV BETHANECHOL
1 50
T 100
[~gm,'Kg]
FIG. 6. LES pressures basally and after increasing doses of bethanechol alone (open circles and broken line) and with chlorpheniramine 40 pg/kg (X'S and solid line).
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
HISTAMINE
ON
LOWIXR
01 BASAL -
3
ESOPHAGEAL
6
12
E45
SPHINCTER
25
50
100
IV BETHANECHOL 1pgm/kg] FIG. 7. thanechol mglkg mh kg, h (.x’s
LES pressures basally and after increasing doses of bealone (open circles and broken line), with cimetidine 1 (filled circles and solid line), and with cimetidine 2 mg/ and solid line).
The interaction between HZ-receptor blockade with constant infusion of cimetidine (1 and 2 mg/kg h) and cholinergic stimulation of the LES with intravenous bolus doses of bethanechol is shown in Figure 7. There is no significant difference between the mean sphincteric pressures to increasing doses of bethanechol alone and those obtained with the combination of bethanechol and cimetidine at infusion rates of 1 and 2 h. l
mg/kg
l
DISCUSSION
The role of histamine in gastrointestinal physiology has been largely centered around gastric secretion with little emphasis on motor effects. The role of histamine and histamine-receptor blockade on the basal, pentagastrin-stimulated, and bethanechol-sti mulated LES was evaluated in the awake baboon, The baboon was chosen for study because of the striking anatomical and physiological similarity to man (3). In addition, the use of an awake, nonanesthetized model has di stinct advantages over previous models in that the sphincter-depressing effect of the anesthetic agents and the variation in depth of anesthesia is avoided (3, 11). The results of our study demonstrate that histamine does have a dose-related pressor effect on the LES smooth muscle and confirm previous in vitro observations of histamine stimulation of the LES in the opossum (7, 15) and of betazole stimulation of the human LES (5). Our study indicates, however, that histamine role in the mai ntedoes not appear to play a significant nance of resting I ,ES tone in the primate because H 1’
receptor blockade with chlorpheniramine, HZ-receptor blockade with cimetidine, and combined histamine-receptor blockade with both agents simultaneously did not alter basal LES pressure. This finding is consistent with recent in vivo studies in man in which no change in resting sphincter pressure was observed after Hzreceptor blockade with various oral doses of cimetidine W) Further, our observations indicate that the stimulatory histamine receptor on the LES smooth muscle of the baboon is of the H, class because this pressor response was blocked by chlorpheniramine, but not by cimetidine. The presence of a stimulatory H, receptor and of an inhibitory H, receptor on the LES has been suggested from in vitro and in vivo studies in the opossum (6). Our data does not support the presence of the postulated HZ-inhibitory receptor in the baboon because cimetidine infusion did not alter basal sphincter pressure or the LES response to exogenous histamine. To further evaluate a possible inhibitory H, receptor and to further clarify histaminergic pharmacology of the LES, dose-response curves were constructed to two agonists for LES contraction: pentagastrin, a gastrointestinal hormone fragment known to cause LES contraction (5) and bethanechol, an analogue of acetylcholine that produces direct muscarinic stimulation of the LES (17). Both pentagastrin and bethanechol produced the expected dose-related pressor responses of the LES muscle. Blockade of either the H, or H, receptors did not alter the response of the LES to pentagastrin or bethanechol, indicating that these two agents act independently of histamine receptors. The lack of modification of pentagastrin stimula tion of the LES by cimeti(15). dine is consistent with other observations One explanation for the divergence of our findings and those found in studies on the opossum (6) may be due to species variation. An alternate explanation may be due tO the use of meti amide rather tha n cimetid ine. for the variance between the We have no explanation two recent studies using the same animal model (opossum) and HZ-blocking agent (metiamide). Because HZ-receptor blockade did not alter the LES pressure or its response to hormonal and cholinergic stimuli, these drugs may be beneficial in the treatment of gastroesophageal reflux as well as other diseases characterized by peptic ulceration. Received
6 O&ber
1977; accepted
in fmal
form
20 February
1978.
REFERENCES 1. BEAVEN, M. A. Histamine. N. Engl. J. Med. 294: 30-36,320-325, 1976. 2. BRIMBLECOMBE, R. W. The pharmacology of cimetidine, a new Hz receptor antagonist. Brit. J. PharmacoL. 53: 435-436, 1975. 3* BROWN, F. C,, R. M. GIDEQN, F. M. VOELKER, AND D. 0. CASTELL. Muscle structure and function of the primate esophagus. Am. J. Vet. Res. In press. 4. BROWNLEE, G., AND I, HARRY, Some pharmacological properties of the circular and longitudinal muscle strips from the guineapig isolated ileum. hit. J. Pharmacol. 21: 544-554, 1963. 5. CASTELL, D. O., AND L. D. HARRIS. Hormonal control of gastroe-
6. 7.
8. 9.
sophageal sphincter strength. N. EngL. J. Med. 282: 866-880, 1970. COHEN, S., AND W. SNAPE. Action of metiamide on the lower esophageal sphincter. Gastroenterology 69: 911-919, 1975. DE CARLE, D. J., M. J. BRODY, AND J. P. CHRISTENSEN. Histamine receptors in the esophageal smooth muscle of the opossum. Gastroenterology 70: 1071-1075, 1976. DODDS, W. J. Instrumentation and methods for intraluminal esophageal manometry. Arch. Internal Med. 136: 515-523, 1976, DUBOIS, A., P. VAN EERDEWEGH, AND J. D. GARDNER. Gastric emptying and secretion in Zollinger-Ellison syndrome. J. Clin.
Downloaded from www.physiology.org/journal/ajpendo at Washington Univ (128.252.067.066) on February 15, 2019.
E46
BROWN,
Invest. 59: 255-263, 1977. 10. FREELAND, G. R., R. H. HIGGS, AND D. 0. CASTELL. The effect of cimetidine on the lower esophageal sphincter in normal subjects. CZin. Res. 24: 284A, 1976. 11. HALL, A. W., A. R. MOSSA, J. CLARK, AND D. SKINNER. The effects of premeditation drugs on the lower esophageal high pressure zone and reflux status of Rhesus monkeys and man. Gut 16: 347-352, 1975. 12. KIRK, R. E. Experimentul Design: Procedures for the Behavioral Sciences. Belmont, Calif: Brooks and Cole, 1968, vol. 1, p. 283. 13. KONTUREK, S. J., T. DEMITRESCU, AND T. RADECK. The role of histamine receptors in the stimulation of gastric acid secretion. Am. J. Digest. Diseases 19: 999-1006, 1974. 14. RANDOLF, W. C., V. L. OSBORNE, S. S. WALKENSTEIN, AND A. P. INTOCCIA. High-pressure liquid chromatographic analysis of
15.
16.
17.
18.
DUBOIS,
AND
CASTELL
cimetidine, a histamine HZ-receptor antagonist, in blood and urine. J. PharmacoL. Sci. 66: 1148-1158, 1977. RATTAN, S., D. COLN, AND R. K. GOYAL. The mechanisms of action of gastrin on the lower esophageal sphincter. Gastroenterology 70: 828-835, 1976. R~CHA e SILVA, M. Histamine and antihistamines. Handbook of Experimental Pharmncology. New York: Springer-Verlag, 1966, vol. 18. RULING, G. T., R. L. FARRELL, AND D. 0. CA~TELL. Cholinergic responses of the lower esophageal sphincter. Am. J. Physiol. 222: 967-972, 1972. WOOD, C. J., AND M. A. SIMKINS (eds). International Symposium on Histamine H2 Receptor Antagonists. London: Smith, Kline & French, 1973.
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