Regional hemodynamic in conscious rats

effects of neuromedin

U

SHEILA M. GARDINER, ALIX M. COMPTON, T. BENNETT, J. DOMIN, AND S. R. BLOOM Department of Physiology and Pharmacology, Medical School, Queen’s Medical Centre, Nottingham NG7 2UH; and Department of Endocrinology, Royal Postgraduate Medical School, London W12 OHS, United Kingdom

GARDINER, SHEILA M., ALIX M. COMPTON,T. BENNETT,J. DOMIN, AND S. R. BLOOM. Regional hemodynamic effects of

neuromedin U in conscious rats. Am. J. Physiol. 258 (Regulatory Integrative Comp. Physiol. 27): R32-R38, 1990.-In conscious unrestrained Long-Evans rats, chronically instrumented with miniaturized pulsed Doppler flow probes, intravenous administration of porcine neuromedin U-8 by bolus (0.1 and 1.0 nmol) or infusion (1 and 10 nmol/h) exerted potent constrictor effects on the superior mesenteric vascular bed. With the choice of an appropriate dose, the reduction in superior mesenteric blood flow was not accompanied by any changes in systemic arterial blood pressure, heart rate, and renal or hindquarters blood flows. Porcine neuromedin U-25 had similar effects to neuromedin U-8, but was generally more potent. In Brattleboro rats the pattern of response to neuromedin U-25 was similar to that seen in Long-Evans rats, indicating that mesenteric vasoconstriction was not dependent on release of endogenous vasopressin. In Long-Evans rats the regional hemodynamic actions of rat neuromedin U were comparable with those of porcine neuromedin U-25. The latter peptide at a dose of 1.0 nmol caused a rise in total peripheral resistance and a reduction in cardiac output, with an inconsistent change in heart rate. The results raise the possibility that the high concentration of neuromedin U in the rat intestine is associated with the control of local blood flow. neuromedin U-8; neuromedin U-25; rat neuromedin; cardiac output; regional blood flow; superior mesenteric vasoconstriction

MINAMINO ET AL. (11) identified

several novel peptides in extracts from porcine spinal cord, including two they designated neuromedin U-8 (NMU-8) and neuromedin U-25 (NMU-25) that contained 8 and 25 amino acids, respectively, and caused uterine contraction and pressor effects in the rat. Subsequent studies utilizing a specific radioimmunoassay for NMU-like immunoreactivity (NMU-LI) (5) demonstrated that this substance was distributed in various tissues in the rat. Domin et al. (5) found high concentrations of NMU-LI in the small intestine where it was confined to the muscular layers rather than the mucosa. A subsequent investigation (1) involving immunohistochemistry confirmed the presence of NMU-LI in the submucous and myenteric plexuses associated with the musculature but localized some reactive nerve terminals to the mucosa and few to the muscle coats (1). In the light of these findings and the R32

0363-6119/90

$1.50 Copyright

observation that neither NMU-8 nor NMU-25 affects contractile activity in isolated guinea pig ileum (11), we investigated the possibility that NMU-8 and NMU-25 might have selective effects on superior mesenteric blood flow in the conscious rat. Initially, we chose the doses used by Minamino et al. (II), which, they showed, had pressor effects in anesthetized rats. However, we also investigated the possibility that lower doses of NMU-8 or NMU-25, given by bolus injections or by infusions, might influence regional hemodynamics without having marked effects on systemic arterial blood pressure; in addition we investigated the cardiac effects of NMU-25 in conscious rats. While this work was in progress the amino acid sequence of rat neuromedin U was determined (4, lo), and small samples of this peptide became available. Therefore, in a separate series of experiments, we investigated the regional hemodynamic responses to rat neuromedin U. Some of the results have been presented in abstract form (3). METHODS

Male Long-Evans and Brattleboro rats (3-4 mo old) were studied. All surgery was carried out under sodium methohexitone anesthesia (60 mg/kg ip supplemented as required) and aseptic conditions. Measurements of regional hemodynamics were made with miniaturized pulsed Doppler probes (8)) chronically implanted around the left renal and superior mesenteric arteries and around the distal abdominal aorta (below the level of the ileocecal artery). In separate Long-Evans rats cardiac output was measured with an electromagnetic flow probe (Skalar MDL 1401) implanted around the ascending aorta by an intrathoracic approach (13, 14). All animals were given an intramuscular injection of ampicillin (7 mg/kg) and were allowed at least 7 days to recover from surgery before they were briefly reanesthetized (sodium methohexitone, 40 mg/kg) for the implantation of intravascular catheters. Catheters for peptide administration were implanted in the right jugular vein. The tip of the intraarterial catheter lay in the distal abdominal aorta, access being through the ventral caudal artery. All catheters were tunneled subcutaneously and emerged at the back of the neck at the same point as the probe wires. The catheters ran through a flexible spring connected to a harness worn by the rat. The spring and the connecting

0 1990 the American

Physiological

Society

Downloaded from www.physiology.org/journal/ajpregu at Macquarie Univ (137.111.162.020) on February 12, 2019.

NEUROMEDIN

Renal

-

Mesenteric - - -~

~_--

Hindquarters -+-_~_

t

Neuromedin U8 (0.1 nmol)

t ’

R33

U AND HEMODYNAMICS

1

5 min

Neuromedin U8 ( lnmol)

FIG. 1. Cardiovascular responses to bolus injections of 2 doses of neuromedin U-8 in the same conscious Long-Evans rat. Low dose produced a marked and rapid reduction in superior mesenteric blood flow only. With higher dose there was a slight reduction in renal blood flow also; increase in blood pressure (BP) was not accompanied by a reflex bradycardia.

lead to the flowmeter were supported by a counterbalanced universally jointed lever system (6). Experiments were begun the following day when animals were fully conscious and unrestrained. In the regional hemodynamic studies, phasic blood pressures and mean blood pressure (BP), instantaneous heart rate (HR), and renal, mesenteric, and hindquarters Doppler shift (DS) signals were monitored continuously. Percentage changes in the DS signals were taken as an index of changes in flow (6-8, 17), and percentage changes in regional vascular resistances were calculated from the

mean BP and mean DS signals (6417). In some experiments continuous recordings were made of vascular resistance changes derived from an analog computer (designed and built in the department) that divided BP by mean DS signals on line. In those experiments in which cardiac output was measured, the pulsatile and electronically derived mean volume flow signals from the electromagnetic probe around the ascending aorta were monitored continuously, together with intra-arterial pressures. Experiments with porcine NMU-8 and NMU-25 and rat NMU were carried out in separate groups of animals, thus avoiding any possibility of cross-desensitization. Base-line recordings of at least 30-min duration were made before the following experiments were carried out. Regional hemodynamic effects of NMU-8. Long-Evans rats (n = 8) were given bolus doses (0.1 and 1.0 nmol) of NMU-8, with at least 1 h between the doses. Thereafter, the same animals were given 60-min infusions of NMU8 (1.0 and 10 nmol/h), separated by at least 1 h. Regional hemodynamic effects of NMU-25. Long-Evans rats (n = 6) were given bolus doses of NMU-25 (0.01, 0.1, and 1.0 nmol) with at least 1 h between each dose. The same animals subsequently were infused with NMU25 (1.0 and 10 nmol/h) for periods of 60 min, the infusions being separated by at least 1 h. Because the mesenteric hemodynamic effects of NMU-25 (see RESULTS) were so similar to those of vasopressin (7), we also investigated the regional hemodynamic effects of NMU25 (protocols as above) in Brattleboro (i.e., vasopressindeficient) rats (n = 9) to control for the possibility that exogenous NMU-25 might be exerting its mesenteric hemodynamic effects through release of endogenous vasopressin. Such an effect is feasible considering the high concentrations of NMU-LI in the hypothalamus (1, 2,

5) .

Regional hemodynamic effects of rat NMU. Long-Evans rats (n = 8) received bolus doses (0.001, 0.01, and 0.1 nmol) of rat NMU, separated by at least 1 h. Subsequently, these animals were infused with rat NMU for 20 min at a dose of 10 nmol/h. When giving rat NMU we were not able to match the doses of NMU-25 because we had insufficient of the former peptide. Cardiac output effects of NMU-25. Long-Evans rats (n

1. Peak (-0.5 min) cardiovascular changes following bolus dosesof porcine neuromedin U-8 or neuromedin U-25 in conscious Long-Evans rats

TABLE

NMU-8,

nmol

0.1

Mean blood pressure, mmHg +6&l* Heart rate, beats/min +9t8 Doppler shift, % Renal -1t2 Mesenteric -24&4* Hindquarters +6t4 Vascular resistance, % Renal +7t3 Mesenteric +42&7* Ok4 Hindquarters Values are means t SE. NMU-8, neuromedin U-8 (n = 8 rats); (Wilcoxon’s test). t P < 0.05 compared with corresponding values

NMU-25,

nmol

1.0

0.01

0.1

1.0

+20*3* +12*11

+6&l* +21t6*

+9*2* +14t9

+23&3* -9t8

-12t2* -36&3* +8t6

O&l -23t3* +12&4

-4t3 -42*5*-f+13&5

-4t5 -60+7*t 13k6

+34t5* +85t8* +12t6

+5t1* +38t4* -5t4

+14*4 +95+18*t -324

+28&6 +245+45*t +10t9

NMU-25, neuromedin U-25 (n = 6 rats). * P c 0.05 compared with base line for NMU-8 (Mann-Whitney test).

Downloaded from www.physiology.org/journal/ajpregu at Macquarie Univ (137.111.162.020) on February 12, 2019.

R34

NEUROMEDIN

t Neuromedin U-25 (0.01 nmol)

U AND

t

Neuromedin U-25 (0.1 nmol)

HEMODYNAMICS

t

l

I

5 min

Neurimedin U-25 (1 .O nmolj

FIG. 2. Cardiovascular responses to bolus injections of 3 different doses of neuromedin U-25 (NMU-25) in the same conscious Long-Evans rat. In this experiment changes in regional vascular resistance were recorded on-line with an analogue computer. Selective mesenteric vasoconstrictor effect of NMU-25 is clearly seen.

= 5) were given bolus doses (0.01, 0.1, and 1.0 nmol) of NMU-25, with at least 60 min between doses. Peptides (porcine NMU-8 and NMU-25, Bachem, UK; rat NMU, custom synthesized by IAF Biochem, Quebec) were dissolved in isotonic saline containing 1% bovine serum albumin; bolus doses were given in 0.1 ml and flushed in with O.l-ml saline. Infusions were given at 0.3 ml/h. Measurements were made over the 1 min immediately preceding any intervention and at the time of maximum response following bolus injections; this corresponded to -0.5 min postinjection. Responses to infusions were assessed from the changes occurring -5 min after the onset of infusion and at the end of the infusion. The changes after infusion were measured at 5 and 20 min after the offset. All data were analyzed by nonparametric two-way analysis of variance (Friedman’s test), Wilcoxon’s rank sum test, or the Mann-Whitney U test as appropriate. RESULTS

Regional hemodynamics. Administration of vehicle (isotonic saline containing 1% bovine serum albumin) was without systematic effect on cardiovascular variables. Bolus injection of NMU-8 (0.1 nmol) caused a slight transient increase in BP accompanied by superior mesenteric vasoconstriction with no other regional hemodynamic changes (Fig. 1, Table 1). Bolus injection of 1.0 nmol of NMU-8 caused an increase in BP; this effect was accompanied by reductions in renal and superior mesenteric blood flows (Fig. 1, Table l), but no systematic change in hindquarters flow or HR. Similar selective effects on mesenteric flow were seen with NMU25, but this peptide was more potent than NMU-8 (Fig.

2, Table 1). The mesenteric vasoconstrictor responses to bolus doses of NMU-25 were similar in Long-Evans (Table 1) and Brattleboro rats (Table 2), although in the latter there were also significant increases in hindquarters flow (Table 2). Infusion of NMU-8 (1 nmol/h) initially reduced superior mesenteric blood flow and increased resistance without any significant changes in other variables (Table 3). At the onset of a l-h infusion of NMU-8 at the higher dose of 10 nmol/h there was a transient increase in BP that was accompanied by a reduction in superior mesenteric blood flow (Table 3). Calculated resistances increased in renal, mesenteric, and hindquarters vascular beds (Table 3). However, after 60 min of infusion, only the superior mesenteric vascular bed showed a reduction in flow, and this reversed to a significant hyperemia TABLE 2. Peak (-0.5 min) cardiovascular changes following bolus dosesof porcine neuromedin U-25 in conscious Brattleboro rats Neuromedin

Mean blood pressure, mmHg Heart rate, beats/min Doppler shift, % Renal Mesenteric Hindquarters Vascular resistance, % Renal Mesenteric Hindquarters

U-25,

nmol

0.01

0.1

1.0

+3t1* +8k4

+18t2* +4*4

+35t2* -9k5

-1t2 -27*2* +22t3*

-4t2 -53t3* +17*5*

-9t2* -63t3* +2O,t7*

+4t1* +41t5* -14t2*

+20&3* +152t13* o-e4

Values are means t SE; n = 9 rats. line (Wilcoxon’s test).

*

P

C 0.05 compared

Downloaded from www.physiology.org/journal/ajpregu at Macquarie Univ (137.111.162.020) on February 12, 2019.

+43t3* +266*32* +11t7 with

base

NEUROMEDIN

U AND

R35

HEMODYNAMICS

3. Cardiovascular changes during and after infusion of porcine neuromedin U-8 in consciousLong-Evans rats

TABLE

NMU-8

Infusion

(1.0 nmol/h)

During Time,

min:

Mean blood pressure, mmHg Heart rate, beats/min Doppler shift, % Renal Mesenteric Hindquarters Vascular resistance, % Renal Mesenteric Hindquarters Values

are means

NMU-8 After

Infusion

(10 nmol/h)

During

After

5

60

5

5

60

5

20

+1t1 +17t14

0s +3t10

-l&l +14*10

+9t3* +7t10

+3t2 +2t7

-2t2 +w7

O&l +4u7

-1*1 -5t2” -l&3

+4&3 -2k7 -3t7

+2&4 +4&8 +lt6

+1&3 -25&3* -4t2

+2&4 -12t3” Ot2

+5t4 +17&6* +3t3

-5t3 +1t5 -4t3

+3tl +8t4* +2+3-

-3t3 +5t7 -I-7&7

-l&4 -1t6 Ot6

+8t3* +47t6* +13&4*

-6t3* -15k4” -4k3

+7t4 +1-1-5 +6t4

k SE; n = 8 rats. NMU-8,

neuromedin

U-8.

*

P

Regional hemodynamic effects of neuromedin U in conscious rats.

In conscious unrestrained Long-Evans rats, chronically instrumented with miniaturized pulsed Doppler flow probes, intravenous administration of porcin...
1MB Sizes 0 Downloads 0 Views