Postjunctional α2-adrenoceptors mediate vasoconstrictin in human subcutaneous resistance vessels

Abstract

In vitro studies have been performed on human medium-sized muscular arteries (internal diameter 1-4 mm) in a classical organ bath and with human subcutaneous resistance arteries (internal diameter 103-626 μm) in a microvascular myograph. Although the medium-sized muscular arteries showed no response to either of the α2-agonists B-HT 933 or Uk 14304 in concentrations up to 10 μM, the subcutaneous resistance arteries from all regions examined showed well-pronounced and concentration-dependent responses to B-HT 933, the pD2 (-log EC50) being 5.11 ± 0.09. In the resistance arteries the α2-antagonist yohimbine caused a parallel shift to the right of the B-HT 933 concentration-response curve; the yohimbine pA2 for the B-HT 933 receptor was 7.86 ± 0.12. There was an inverse relationship between the maximum response to B-HT 933 and the calibre of the resistance vessels. These results indicate the presence of a postjunctional α2-adrenoceptor in human subcutaneous resistance arteries and not in medium sized muscular arteries.