Desensitization of the vascular contractile response to cumulative doses of α2-adrenoceptor agonists

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Abstract
Contractile responses to single or cumulative doses of α-adrenoceptor agonists were compared in the tail artery and the saphenous vein of the rat. In the rat tail artery, there were no differences in the dose–response relationships to noradrenaline, methoxamine, and KCl whether the agonists were applied as single or cumulative doses. However, the responses to single doses of clonidine and B-HT 920 were significantly larger than similar doses applied cumulatively. In the rat saphenous vein, responses to single doses of noradrenaline, clonidine, and B-HT 920 were also significantly larger than the corresponding cumulative doses. However, there was no difference in the responses to KCl. It was suggested that desensitization of α2-adrenoceptors in these vessels may result in the diminished responses to cumulative doses of the agonists. Desensitization appeared to be specific to α2-adrenoceptors, since the effect was not observed in responses mediated by the α1-adrenoceptors and KCl.