Desensitization of the vascular contractile response to cumulative doses of alpha 2-adrenoceptor agonists.
Contractile responses to single or cumulative doses of alpha-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 alpha 2-adrenoceptors in these vessels may result in the diminished responses to cumulative doses of the agonists. Desensitization appeared to be specific to alpha 2-adrenoceptors, since the effect was not observed in responses mediated by the alpha 1-adrenoceptors and KCl.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000187:drug effects; D001381:Azepines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012501:Saphenous Vein / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011189:Potassium Chloride; C024763:talipexole; D008729:Methoxamine; D009638:Norepinephrine