1. In chloralose-anaesthetized cats the centrally induced hypotensive effect of clonidine, and in some cases α-methyldopa, was diminished by pretreatment with a variety of tricyclic antidepressants and neuroleptic agents.
2. The interaction is assumed to occur at the central α-adrenoreceptors. Clonidine or α-methylnoradrenaline (from α-methyldopa) are the agonists, and the aforementioned psychotropic drugs are the antagonists.
3. Psychotropic drugs which are not α-receptor blockers, like butyrophenone neuroleptics (pimozide and haloperidol) or benzodiazepine tranquillizers, do not significantly diminish the centrally induced hypotensive effect of clonidine.