Endothelial mechanism in the vascular action of hydralazine.

Relaxation of precontracted isolated chains of aortic rings with intact endothelium and in those with the endothelium removed was studied in response to various antihypertensive vasodilator drugs. Of the drugs tested--nitroprusside, nitroglycerin, prazosin, minoxidil, diazoxide and hydralazine--only the vascular relaxant effects of hydralazine were found to be dependent, in part, on the presence of intact endothelium. The endothelial component of the hydralazine response represented a major contribution to the net relaxant effect on the vascular smooth muscle, particularly at lower concentrations, 90 nM to 1 microM, which are also clinically relevant.