RESUMO
We investigated the alpha(1)-adrenoceptor subtype(s) involved in contraction of the isolated rat mesenteric artery by the use of the agonists noradrenaline (NA), phenylephrine (PHE), oxymetazoline (OXY), and methoxamine (MET), the competitive antagonists 8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspiro(4.5)decane-7,9-dione dihydrochloride (BMY 7378) and 5-methylurapidil, and the alkylating agent chloroethylclonidine (CEC). Agonists showed the potency order NA> or =PHE>OXY>MET; pA(2) values for 5-methylurapidil and BMY 7378 were 7.74+/-0.11 and 8.72+/-0.28, respectively, while Schild slopes were not different than unity; alpha(1)-adrenoceptor alkylation with CEC showed a drastic decrease in maximal agonists-induced contraction and a shift to the right of about 46-, 122-, 2-, and 15-fold higher than controls for NA, PHE, OXY, and MET, respectively. Data suggest that alpha(1D)-adrenoceptors predominate for contraction in mesenteric artery of the Wistar rat, with a second population of alpha(1A)-adrenoceptors responding at high agonist concentrations.