title: Enhancement effect of carteolol on the clonidine-induced vasodilation of rat mesenteric arteries.
abstract: It has demonstrated that carteolol can increase the endothelium-dependent vasodilation induced by alpha-2 adrenergic agonist. In order to evaluate the effect of carteolol, and to clarify the mechanism, we examined the effects of 10 microM carteolol on the vasodilation induced by increasing doses (10(-7)-10(-4) M) of clonidine in perfused rat mesenteric arteries preconstricted with 100 microM phenylephrine. Clonidine elicited a dose-dependent vasodilation of the mesenteric arteries preconstricted with phenylephrine. Carteolol enhanced the vasodilation induced by higher doses (10(-5) and 10(-4) M) of clonidine, although carteolol itself exerted no direct vasodilating effect. On the other hand, 10 microM propranolol or 10 microM metoprolol did not augment the clonidine-induced vasodilation. In the presence of 100 microM NG-monomethyl L-arginine (LNMMA), an analogue of L-arginine, the enhancement of the clonidine-induced vasodilation by carteolol was abolished. This inhibition by LNMMA was restored with 300 microM L-arginine, but not with 300 microM D-arginine. These results suggest that carteolol enhances the clonidine-induced vasodilation by an endothelial-related mechanism mediated by the release of endothelium-derived nitric oxide in resistance vessels.
mesh_terms: D000818:Animals; D002354:Carteolol / Q000494:pharmacology*; D003000:Clonidine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D014665:Vasodilator Agents; D002354:Carteolol; D003000:Clonidine