alpha(1)-Adrenergic receptor subtypes in rat cerebral microvessels

To identify alpha(1)-adrenergic receptor subtypes involved in the regulatio n of cerebral microcirculation, we studied alpha(1)-adrenergic receptor sub types expressed in the rat cerebral microvessels. The microvessels were pre pared from rat cerebral cortex by albumin flotation and glass bead filtrati on techniques. [I-125]HEAT binding to the cerebral microvessels was displac ed by low concentrations of 5-methylurapidil, a selective antagonist for al pha(1)-receptors, and modified Scatchard analysis of the data revealed that half of alpha(1)-receptors is alpha(1A)-subtype, and that alpha(1B)- and/o r alpha(1D)-receptors are also present. The K-i value of the high-affinity component for 5-methylurapidil was 3.90+/-1.08 nM, which is comparable with the value obtained in the rat cerebral cortex (2.17+/-0.88 nM). Reverse tr anscription and polymerase chain reaction experiments showed that mRNAs of alpha(1A)- and alpha(1B)-receptors, but not alpha(1D)-receptors, were expre ssed in the cerebral microvessels. These results suggest that alpha(1)-rece ptors involved in the regulation of cerebral microvessel function are alpha (1A)- and alpha(1B)-receptor subtypes. (C) 2000 Elsevier Science B.V. All r ights reserved.