Central effects of alpha-adrenoceptor agonist and antagonist drugs on somatically evoked reflexes in cat systemic and hindlimb circulations.

Abstract

1. A study was made of the effects of centrally administered alpha-adrenoceptor agonist drugs on the pressure changes elicited by somatic afferent nerve stimulation using chloralose-anaesthetized cats with autoperfused hindlimb circulations. 2. Clonidine, noradrenaline and adrenaline, given intracisternally, differed in their effects on the magnitude and duration of the systemic component of the somatic pressor reflex. None of these drugs significantly affected the hindlimb component of this reflex. 3. The selectivity of these drugs for the different reflex components may be explained by the different haemodynamic characteristics of the systemic and hindlimb circulations. 4. Intracisternal injection of the alpha-adrenoceptor antagonist piperoxan after the agonist drugs resulted in a complex pattern of responses affecting both the systemic and hindlimb reflex components. This suggests that the central pharmacological mechanisms involved may modulate more subtle changes in cardiovascular function than might be indicated by observations made in intact animals.