Sudies About the Pressor Response to Intracerebroventricular Infusion of Hypertonic NaCl in Rabbits

Baik, Yung Hong; Choi, Song Youn; Lee, Choong Kyoung

Abstract

Changes of blood pressure, heart rate, ECG, respiration rate and pupil size by intracerebroventricular(ICV) infusion of hypertonic NaCl with 0.04 ml/min for 5 min(total 0.2ml) were observed in urethane-anesthetized rabbits. ICV infusion of 0.75M NaCl produced slight pressor effect (11mmHg) and did not affect other parameters. ICV infusion of 1.5M NaCl began to increase blood pressure from 2~3 min after the infusion and produced maximal increase(24mmHg) at 5~10 min. Then the pressor effect was recovered to the original level at 30~60 min. Change of heart rate by the infusion was not clear, but ST-segment of ECG was markedly depressed. Respiration rate increased about 1.5 times than the control in accordance with the pressor effect and the state was continued even after the recover of the pressor effect. Both pupils dilated markedly and light-reflex was lost. Changes of parameters by ICV infusion of 3.0M NaCl were similar to those by 1.5M NaCl and some rabbits caused severe arrhythmias and died. The purpose of present study is to investigate the mechansim(s) of the pressor effect induced by the ICV infusion of 1.5M NaCl. The pressor effect of 1.5M NaCl was attenuated by the continuous infusion of vasopressin antagonist(20microm/kg/min) but not affected by intravenous treatment with 2mg/kg phentolamine, 2mg/kg propranolol and 1mg/kg chlorisondamine. The pressor effect was not altered with ICV 0.12mg/kg phenoxybenzamine, 0.4mg diltiazem, 0.1mg/kg mecamylamine and 0.2mg/kg atropine. After ICV infusion of 25microg/kg/min of diazepam, however, the pressor effect was completely abolished and restored 3~4 hours after stopping diazepam infusion. The pressor effect was rather potentiated than inhibited in bilateral adrenalectomized or nephrectomized rabbits. Infusion of 2microg/kg/min of saralasin for 10 min in the bliateral adrenalectomized rabbit did not affect the pressor effect at all. These results suggest that hypertensive effect induced by ICV infusion of hypertonic NaCl is mediated by the increase of vasopressin secretion.