Interactions between prazosin, clonidine and direct vasodilators in the anaesthetized rat

1. Prazosin, clonidine, hydrallazine and diazoxide were administered intravenously, alone or in various combinations, to anaesthetized rats. 2. Prazosin and clonidine were equipotent. Their combined hypotensive effects in no instance exceeded the maximum effect attainable with either agent alone. The hypotensive effects of hydrallazine or diazoxide were, in contrast, additive to those of either prazosin or clonidine. 3. Pressor responses to clonidine were antagonized by prazosin. Prazosin may prove useful in hypertensive crises provoked by clonidine.