Local temperature modulates alpha 1- and alpha 2-adrenergic vasoconstriction in men.

Previous work in the canine saphenous vein has shown that cooling augments alpha 2- but not alpha 1-mediated contractile responses and that warming produces the opposite effects. Here we sought to determine whether these results occur in the human finger, a cutaneous vascular bed. Healthy men received brachial artery infusions of phenylephrine and clonidine with and without yohimbine while sympathetic tone was reduced by hearing the legs. Finger blood flow was recorded by venous occlusion plethysmography from two fingers, one cooled and one uncooled, on each hand. Cooling augmented alpha 2-adrenergic vasoconstriction produced by clonidine; this effect was reduced by yohimbine, an alpha 2-adrenergic antagonist. In contrast, cooling abolished alpha 1-adrenergic vasoconstriction produced by phenylephrine, which was not affected by yohimbine. Further studies were conducted in which fingers were warmed rather than cooled. Warming augmented alpha 1- but reduced alpha 2-adrenergic vasoconstriction. Thus, in human fingers, cooling augments alpha 2- and suppresses alpha 1-adrenergic vasoconstriction, whereas warming produces the opposite effects.