Forearm Venous Responses to Stimulation of Adrenergic

The properties of the adrenergic receptors in the veins or capacitance vessels of man have not been defined completely. Norepinephrine causes constriction of resistance vessels by stimulation of alpha receptors (2); it also causes constriction of the veins or capacitance vessels (3-5). Iso-proterenol causes dilatation of resistance vessels by stimulation of beta receptors (6), but reports of its action on the capacitance vessels are con-flicting. It appears to cause forearm venous con-striction when administered systemically (7), but dilatation is said to occur with infusion into the brachial artery (8). The experiments to be re-ported here were done to investigate the effects of stimulation of alpha and beta receptors in the veins of the forearm of man in a systematic fashion. Methods The subjects were healthy male volunteers ranging in age from 21 to 27 years. They were studied while lying in the supine position. Drugs that stimulate or block adrenergic receptors were infused or injected through polyethylene tubes inserted into the left brachial artery or into a systemic vein. Forearm blood flow and venous distensibility were measured in the left forearm with a water plethysmograph. In some experiments, transmural venous pressure was recorded through polyethylene tubes inserted into superficial veins in the segment of forearm enclosed in the plethysmograph. Arterial pres-* Submitted for publication December 28, 1964; ac