Effects of intracerebroventricular (I.C.V.) administration of 5-hydroxytryptamine (5-HT) on hemodynamics in conscious spontaneously hypertensive rats (SHR): relation to sympathetic nervous system

Abstract

Recently, the serotonergic nervous system has been receiving attention as part of the blood pressure regulating mechanism of the central nervous system, and it has been postulated that the system may participate in the pathogenesis of hypertension. The purpose of this experiment is to investigate the mechanism of hemodynamic change after i.c.v. administration of 5-HT in SHR and in normotensive Wistar Rats (WR). Twenty-week-old male SHR (n = 11) and age-matched WR (n = 14) were used. On the day before the experiments, the unilateral carotid artery and jugular vein were cannulated. Also, a cannula was inserted stereotaxically into the anterior horn of the lateral cerebral ventricle. Experiments were performed under the conscious and minimum restrained state. Experiment I: After observation of resting mean arterial pressure (MAP) and heart rate (HR) for 20 minutes, 5-HT (5 micrograms/5 microliter saline) was administrated i.c.v., and MAP and HR were observed for 90 minutes. Then, 200 micrograms of phenoxybenzamine (POB) was given from the jugular cannula. Thirty minutes after the POB administration when MAP was stabilized, 5 micrograms of 5-HT was again given i.c.v., and MAP and HR were recorded for 30 minutes. Experiment II: Plasma norepinephrine (PNE) was measured before and 2 minutes after 5-HT i.c.v. administration. The control sample (1.5 ml) was withdrawn at least 30 minutes before the 5-HT injection, and immediately after the blood sampling, the same amount of blood which was obtained from the age-matched donor rat of the same strain was transfused. Experiment I: Resting MAP was 136.4 +/- 5.1 mmHg in SHR and 99.1 +/- 3.0 mmHg in WR. I.c.v. administration of 5-HT elicited consistent pressor response in SHR and in WR.(ABSTRACT TRUNCATED AT 250 WORDS)