Vascular effects of ipsapirone are related with subtypes of alpha 1-adrenergic receptors

RESUMO

The aim of this study was to provide further evidence about the participation of Ó1-adrenoceptors in the vascular responses elicited by impsapirone. This 5-HT 1A agonist displayed vasodilator activity only when aortic rings were precontracted by Ó-adrenergic compounds. The relaxant effect was particulary evident when rings were precontracted with methoxamine (selective Ó1A-adrenergic agonist).On the other hand, ipsapirone but chloroethylclonidine (selective Ó1B-adrenergic antagonist), clearly displaced norepinephrine and methoxaminevasocontractile concentration-response curves to the right. Fanally, ipsapirone protected the Ó-adrenoceptors from the irreversible blockade provoked by phenoxybenzamine, as judged by thenorepinephrine contraction and stimulated phosphatidylinositil labeling. Accordingly the relaxant effect elicited by ipsapirone in aortic rings precontracted with Ó-adrenergic agonists and the protective action against blockade by phenoxybenzamine shown by this agent are proof of its ability to occupy Ó1-adrenoceptors. Specifically, Ó1A-adrenergic receptors seem to be involved in ipsapirone vascular effects, since this agent selectively relaxed aortic preparation precontracted with methoxamine and unlike chloroethylclonidine, clearly inhibited the contractile effect of this agonist. In summary, the present findings can be explained by accepting that ipsapirone may act as an antagonist at Ó1A-adrenoceptors