Effect of clonidine on blood pressure alterations induced in spinal cats

Blood pressure alterations were evoked by stimulation of spinal pathways descending in the dorsolateral funiculus of chloralose-anesthetized cats, spinalized at the C1 level. Intravenous clonidine was found to attenuate threshold, intermediate, and maximal pressor responses (elicited by increments in current delivery) in a dose-related manner. The pressor responses following norepinephrine administration (0.2 micron/kg, i.v.) were somewhat potentiated by clonidine in these animals. Furthermore, this agent was found ineffective in blocking blood pressure alterations occurring in response to T3 or T4 white ramus stimulation at several frequencies. It is concluded that clonidine has a significant inhibitory action at the spinal level.