Cooling enhances alpha 2-adrenoceptor-mediated vasoconstriction in human hand veins

Abstract

The contribution of different receptor subtypes in the contractile response during cooling in human hand vessels is of considerable interest in the understanding of cold-induced peripheral vasospasm as it appears in Raynaud's phenomenon. Subcutaneous vein segments from 50 patients undergoing hand operations not related to vascular disorders were examined in vitro. The temperature in the organ bath was initially 37 degrees C and was either continuously lowered to 10 degrees C or kept constant at 37 degrees C, 29 degrees C or 20 degrees C. The characteristics of the alpha-adrenoceptor-mediated motor response were elucidated with the use of the alpha 1-antagonist, prazosin, and the alpha 2-antagonist, yohimbine. A great variability between individuals in the proportions of alpha 1- and alpha 2-adrenoceptors was found. In the majority of the vessels continuous cooling to 25 degrees C augmented a noradrenaline-induced contraction. This augmentation was unaltered in the presence of prazosin but abolished by yohimbine, suggesting that it was mediated via the alpha 2-adrenoceptor. In the remaining vessels with a predominating alpha 1-adrenoceptor-mediated response a cold-induced relaxation was registered. This could be the result of a reduced alpha 1-adrenoceptor-mediated contraction at this low temperature. These varying reactions to cooling were unaffected by the beta-antagonist, propranolol, and by endothelial denudation. The results obtained in corresponding experiments with the alpha 1-agonist methoxamine and alpha 2-agonist, oxymetazoline, were conflicting, probably due to the poor selectivity of these agonists in human tissues.(ABSTRACT TRUNCATED AT 250 WORDS)