Histaminergic H1-receptors in smooth muscle and endothelium of bovine thoracic aorta.

The vascular endothelium modulates relaxation and contraction of blood vessels. Since endothelial cells respond to a variety of vasoactive substances, it was suggested that specific cell membrane receptors exist on the endothelial cells which are responsible for the modulatory role of the endothelium on the blood vessels. We therefore investigated the localization and binding characteristics of histaminergic H1-receptors in the vascular model system of the bovine thoracic aorta. Our earlier binding experiments showed that histaminergic H1-receptor binding sites labelled with [3H]mepyramine are present on the vascular smooth muscle membranes of this tissue. In addition a small number of specific H1-receptor binding sites also exist on the endothelial cells of this tissue with the following binding characteristics: Bmax = 34.6 fmol [3H]mepyramine/mg protein, KD = 2.13 nM. [3H]mepyramine binding is more effectively inhibited by H1- than H2-receptor agonists and antagonists. These results provide evidence for the existence of endothelial histaminergic H1-receptor binding sites in addition to vascular smooth muscle H1-receptors in the bovine thoracic aorta.