Effects of alpha-methyldopa on blood pressure in the anaesthetized dog

Intravenous infusion over 1 h of 20 mg kg(-1) of alpha-methyldopa produced hypotension in the anaesthetized dog. The magnitude of this effect was, however, inversely correlated with bodyweight. Either rapid intravenous injection of alpha-methyldopa or slow infusion of alpha-methyldopate, was less effective in lowering blood pressure than infusion of free alpha methyldopa in dogs of equivalent bodyweight. Infusion of alpha-methyldopa into a vertebral or internal carotid artery produced hypotensive responses but these were no greater and generally less than those obtained to intravenous infusion. alpha-Methyldopa was therefore capable of producing hypotension in the dog but no evidence was obtained for this being the result of an action within the brain.