Alpha-adrenoreceptors and muscarine receptors in human pial arteries and microvessels: a receptor binding study.

Human pial arteries and intraparenchymal microvessels were isolated for enzyme assays and radioligand binding studies of receptors. Special attention was paid to contamination with brain tissue, which was assessed by luxol staining and cerebroside assays for myelin and by scanning electron microscopy. The amount of contamination was approximately 1% for pial vessels and 14% for microvessel preparations. Significant levels of alpha 1-adrenoreceptors (binding sites for [3H]prazosin) and alpha 2-adrenoreceptors (sites labeled by [3H]azidoclonidine) were found in both types of vessels, suggesting that each receptor can modify contractility in these human vessels. Levels of muscarine receptors (sites labeled with [3H]quinuclidinyl benzilate) and choline acetyltransferase activity were considered significant only in pial vessels.