Studies in the rat on endralazine, a new antihypertensive drug structurally related to hydralazine.

1. The effects on blood pressure, heart rate and plasma renin activity of a new hydralazine congener, endralazine, were evaluated in anaesthetized rats. Dose-response relationships for endralazine, hydralazine and diazoxide, administered intravenously, were compared, and the interactions of endralazine with the ganglionic blocking agent, pentolinium, or with adrenaline, noradrenaline and angiotensin II were examined. 2. In the dose range 0.05 to 1.0 mg/kg, endralazine produced prompt dose-related reductions in systolic and diastolic blood pressure, with relatively little effect on heart rate. The drug had a pronounced dose-related renin stimulating effect. 3. Endralazine retained approximately 80% of its hypotensive activity after pretreatment with pentolinium, and caused no significant attenuation of pressor responses to adrenaline, noradrenaline or angiotensin II. 4. Endralazine was an effective hypotensive agent, with a prompt onset of action, a prolonged and stable effect, and a potency at least twice that of hydralazine and 20 to 25 times that of diazoxide. The data are consistent with a predominantly direct vasodilator mode of action.