Alpha 1- and alpha 2-adrenoceptor agonist-induced contraction in rat mesenteric artery upon removal of endothelium.

Contractile response to norepinephrine, methoxamine and clonidine were determined in rat mesenteric arteries with and without an intact endothelium. Removal of the endothelial cell layer markedly enhanced the maximum contractile effect of norepinephrine (2.8 fold), methoxamine (4.0 fold) and clonidine (13.0 fold). Furthermore, there was a significant decrease in the EC50 values for these agonists. These findings indicate that both alpha 1- and alpha 2-adrenoceptor agonists can induce contraction of mesenteric arteries which is modulated by the endothelial cell layer.