Comparative dilator effect of verapamil and sodium nitroprusside in forearm arterial bed and dorsal hand veins in man: functional differences between vascular smooth muscle in arterioles and veins.

Verapamil and sodium nitroprusside induce a dose dependent dilatation in the forearm arterial bed and preconstricted dorsal hand vein in man. Verapamil is about twenty times more effective in dilating arterioles than veins; sodium nitroprusside is about ten times more effective in veins than arterioles. These differences can be related to functional differences between the two types of vessel.