[The effects of the intracerebroventricular administration of 5-hydroxytryptamine on hemodynamics in conscious rats. Participation of the serotonin receptor and the sympathetic nervous system].

We have previously reported that the intracerebroventricular (i.c.v.) administration of 5-hydroxytryptamine (5-HT) in conscious rats elicited significant pressor response, which was accompanied with an increase in plasma norepinephrine and the pressor response, was abolished by peripheral phenoxybenzamine pretreatment. For further investigation of the relationship between the serotonergic nervous system and the sympathetic nervous system, the effect of either i.c.v. or intravenous (i.v.) serotonin receptor antagonist, methysergide pretreatment on hemodynamic response to centrally administrated 5-HT was studied. Male Wistar rats weighing approximately 250g were used. On the day before the study, the unilateral carotid artery was cannulated (PE-50) to facilitate mean arterial pressure (MAP) and pressure triggered heart rate (HR) observation. Also, a cannula (PE-10) was inserted stereotaxically into the anterior horn of the lateral cerebral ventricle. The experiment was performed under a conscious and minimumly restrained state. After the observation of resting MAP and HR for at least 20 minutes, 5 microgram of 5-HT was given i.c.v. and MAP and HR were recorded for 50 minutes. Then, the rats were divided into two groups, one group (n = 9) received 1 microgram of i.c.v. methysergide and the other group (n = 10) received 1 mg/kg of i.v. methysergide. Ten minutes after either methysergide i.c.v. or i.v. treatment, 5 microgram of 5-HT was administrated i.c.v. again, and MAP and HR were observed for 30 minutes. Resting MAP and HR were 101.6 +/- 3.0mmHg and 413.8 +/- 20.0/min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)