Identification of Vascular Postsynaptic α1- and α2- Adrenoceptors in Man

• Published in: Circulation research Vol. 54; no. 4; pp. 447 - 452
• Main Authors: Jie, Kenneth, van Brummelen, Peter, Vermey, Pieter, Timmermans, Pieter B.M.W.M, van Zwieten, Pieter A
• Format: Journal Article
• Language: English
• Published: American Heart Association, Inc 01-04-1984
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.54.4.447

We studied postsynaptic a-adrenoceptors in human blood vessels by measuring the influence on forearm blood flow induced by intra-arterial infusions of selective α1- and α2- adrenoceptor agonists (methoxamine, B-HT 933, clonidine and guanfacine) and antagonists (doxazosin and yohimbine). The studies were done in healthy volunteers, and forearm blood flow was measured by plethysmography. All agonists produced a significant and dose-dependent vasoconstriction. The effect of B-HT 933 was completely abolished by the concomitant infusion of yohimbine, whereas it was hardly influenced by doxazosin. The effect of methoxamine was prevented by doxazosin and little influenced by yohimbine. The vasoconstriction by clonidine and guanfacine was partially prevented by both doxazosin and yohimbine. The single intra-arterial infusion of yohimbine, as well as doxazosin, resulted in vasodilation. These findings provide strong evidence for the existence of postsynaptic α1- as well as α2-adrenoceptors, both mediating vasoconstriction and contributing to basal vascular tone. The (patho-)physiological significance of this subdivision of a-adrenoceptors remains to be elucidated.