The reversal of clonidine-induced hypotension by protriptyline and desipramine.

The present paper deals with further studies on the interaction between clonidine and tricyclic antidepressants. The pronounced central hypotensive action of 1 mug clonidine/kg, administered into the left vertebral artery of chloralose-anaesthetized cats was readily reversed by protriptyline (300 mug/kg), infused via the same route shortly after the development of the maximum hypotensive effect of clonidine. In earlier studies it has been demonstrated that pretreatment with tricyclic antidepressants significantly diminishes the central hypotensive action of clonidine. This interaction has been presumed to occur at the level of central alpha-adrenoreceptors, where clonidine would be the agonist and tricyclic antidepressants the antagonist. The present findings suggest that a competitive antagonism at the central level, which can occur in either sense, may be involved.