Effect of Clonidine on Blood Pressure, Heart Rate and Body Temperature in Conscious Rats

Abstract

Effects of clonidine on blood pressure, heart rate and rectal temperature in conscious rats were examined. Clonidine (0.1-1 mg/ks s.c.) caused a prevailing pressor response and dose-dependently a fall in heart rate and body temperature. The pressor response to clonidine (0.3 mg/kg s.c.) was completely reduced by phentolamine (10 mg/kg s.c.), chlorpromazine (10 mg/kg s.c.) but not by hexamethonium (30 mg/kg i.p.), guanethidine (30 mg/kg s.c.) or reserpine (5 mg/kg s.c. 18 h + 1 mg/kg i.p. 4 h prior to clonidine). A remarkable potentiation of the pressor response to clonidine was observed after treatment with reserpine. The bradycardia with clonidine (0.3 mg/kg s.c.) was significantly reduced by phentolamine, chlorpromazine or atropine (5 mg/kg s.c.) but was potentiated by reserpine. The hypothermia with clonidine (0.3 mg/kg s.c.) was not influenced by phentolamine or atropine but was significantly potentiated by chlorpromazine. The prevailing pressor response to clonidine in conscious rats appears to be due to a stimulation of peripheral .alpha.-adrenoceptors. The bradycardia with clonidine is probably exerted through the sympathetic pathway and the baroceptor-vagal reflex. The hypothermia with clonidine is probably mainly due to the central mechanism.