Abstract
The stainless steel cannula inserting method was used to observe vascular effects of α-adrenoceptor agonists, phenylephrine (PE), methoxamine (ME), clonidine (CL)and xylazine (XY), on the isolated, perfused rabbit common carotid, renal and femoral arteries. PE and ME induced a dose-dependent vasoconstriction that was readily suppressed by treatment with bunazosin, an α1-adrenoceptor blocker. CL induced a constriction only in common carotid arteries, and this was readily suppressed by bunazosin. In preparations preconstricted by phenylephrine, CL and XY dose-dependently induced vasodilations in the 3 types of arteries, and these vasodilations were not modified by a potent α2-adrenoceptor antagonist, midaglizole. In preparations preconstricted by prostaglandin F2α, CL and XY did not produce any significant vasodilation, but CL induced a vasoconstriction in common carotid arteries that was completely blocked by bunazosin. Thus, it is concluded that: 1)α1-adrenoceptors are functionally predominant in rabbit peripheral arteries, 2)the α2-adrenoceptor agonist-induced vasodilation may be due to an antagonistic action towards α1-mediated constrictions, and 3)clonidine has α1-adrenoceptor stimulating properties in rabbit common carotid artery but not in renal and femoral arteries.
