Abstract
Perfused saphenous vascular bed of dogs anesthetized with pentobarbital responded with vasoconstriction to electrical stimulation of the saphenous nerve and to intra-arterial injections of tyramine and noradrenaline. Since the vasoconstriction caused by stimulation of the saphenous nerve was greatly diminished by phenoxybenzamine, it is evident that the response was elicited by excitation of postganglionic adrenergic fibers in that nerve. The vasocon-striction produced by nerve stimulation was readily abolished by tetrodoxotin. In contrast, like the response to noradrenaline, the vasoconstriction elicited by ty ramine was not reduced at all by tetrodotoxin, and instead rather augmented in some experiments. These results demonstrate clearly that the action of tryamine, i.e., the release of endogenous noradrenaline from postganglionic adren-ergic nerve endings, is not mediated by excitation of those fibers.
