Effects of blockade of alpha- and beta-adrenoceptors and neuropeptide Y(1) receptors, as well as brachial plexus blockade, on endothelium-dependent vasodilation in the human forearm.

1. The aim of the present study was to investigate the effects of alpha-adrenoceptor blockade (phentolamine), beta-adrenoceptor blockade (propranolol), neuropeptide Y(1) receptor blockade and neurogenic blockade (brachial plexus) on endothelium-dependent vasodilation (EDV) in the human forearm. 2. Forty-four young healthy volunteers underwent forearm blood flow (FBF) measurements, using venous occlusion plethysmography, during local intra-arterial infusions of methacholine (MCh; inducing EDV) and sodium nitroprusside (SNP; inducing endothelium-independent vasodilation (EIDV)). These measurements were undertaken at baseline and were repeated with either concomitant local intra-arterial infusion of phentolamine (n = 8), propranolol (n = 7) or saline (n = 6) in the forearm, neuropeptide Y(1) receptor blockade (n = 12) given i.v. or during axillary plexus blockade (n = 11). 3. Both alpha-adrenoceptor blockade and neurogenic blockade induced an upward shift in the dose-response curve for both EDV and EIDV. beta-Adrenoceptor blockade did not change resting FBF or EIDV, but induced a significant decrease in EDV (P = 0.015). Neuropeptide Y(1) receptor blocker induced no significant changes in resting FBF, EDV and EIDV and neither did saline. No changes in blood pressure or heart rate were induced by any of the blockades. 4. Whereas beta-adrenoceptor blockade impaired EDV, alpha-adrenoceptor blockade and neurogenic blockade caused a general vasodilation that was not endothelium dependent. Neuropeptide Y does not seem to influence blood flow in the resting forearm.