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
Assuntos
Animais , Coelhos , Norepinefrina/farmacologia , Fenoxibenzamina/farmacologia , Receptores Adrenérgicos alfa/farmacologiaRESUMO
The intramural branches of the coronary arteries of dogs were studied using venilite casts. The intramyocardial vessels have a general pattern with straight branches that cross from the epicardium toward the endocardium. Many branches were observed throughout the extension of these vessels, mainly in the subendocardium, where there is a rich interconnecting plexus. Some branches divides immediately in the subepicardium. These anatomic findings concur with the observations that the subendocardium is more susceptible to ischemia, as it is dependent on an extensive vascularization. These anatomic findings indicate that during constant underperfusion, the alpha adrenergically mediated vasoconstriction of the subepicardial vessels have an unexpected beneficial effect because of decreased transmural steal.
Assuntos
Vasos Coronários/anatomia & histologia , Modelos Anatômicos , Animais , Circulação Coronária/efeitos dos fármacos , Cães , Receptores Adrenérgicos alfa/farmacologia , Vasoconstrição/efeitos dos fármacosRESUMO
Os autores estudam a distribuiçäo dos vasos coronarianos intramurais, através de moldes plásticos de vinilite, obtidos de coraçöes de cäo. Fporam estudados 6 moldes, de coraçöes injetados com vinilite e corroídos com ácido clorídrico. Os achados revelam que os vasos intramurais nascem de artérias situadas no epicárdio e que penetram em ângulo reto ou com pequena obliqüidade, na musculatura ventricular. Os vasos intramurais caminham até o subendocárdio, como um eixo, emitindo pequenos ramos em todo seu trajeto. Mais raramente observam-se ramos terminais para o subepicárdio. Ao nível do subendocárdio verifica-se uma extensa ramificaçäo vascular, que dá ao molde a aparência de uma penugem, com ampla anastomose para os vasos vizinhos, formando plexo vascular subendocárdico. Estes achados anatômicos estäo coerentes com a observaçäo de que a vascularizaçäo subendocárdica deva ser mais exuberante, para compensar o consumo de oxigênio nesta regiäo e a oposiçäo ao fluxo pela pressäo intracavitária. Com esta base anatômica é possível entender que em situaçöes de hipoperfusäo, o fluxo sangüíneo subendocárdico é mantido por vasoconstricçäo de vasos subepicárdicos. Há evidência na literatura de que esta açäo vasoconstrictora é mediada por receptores alfa adrenérgicos. A açäo de drogas vasodilatadoras que atuam nos pequenos vasos subepicárdicos, levaria a um desvio de fluxo com isquemia subendocárdica