[Antinoradrenergic activity of raubasine on isolated thoracic aorta and vas deferens of rat (author's transl)].

1. The type and intensity of antagonism exerted by yohimbine and raubasine on the noradrenaline action have been studied in vitro. 2. Cumulative dose-response curves with noradrenaline as the agonist, were made using isolated thoracic aorta and vas deferens of rat kept in a Krebs solution. When an antagonist shift the curve to the right the competitive nature of the interaction was verified by assessing the regression straight line of log (x-I) on log (antagonist concentration) and calculation of pA2. 3. In rat isolated vas deferens, the isotonic contractile response to low doses of noradrenaline were antagonized and those to high does potentiated by raubasine. The alpha-adrenoceptor blocker thus caused a shift to the right and an increase of the maximum height of log dose-response curves of alpha-adrenoceptor stimulant. Yohimbine shift the dose-response curves to the right without change of maximal contraction. The curves were analysed with the Schhild plot, and the slopes obtained 0.82 (Yohimbine), 0.96 (Raubasine) were not significantly different from I. The pA2 value is of 6.10 for yohimbine and of 6.50 for raubasine. In the presence of cocaine, which blocks the neuronal uptake, the dose-response curves were shifted to the right in parallel without alteration of maximal contraction. The pA2 value is of 6.57 for yohimbine and of 6.75 for raubasine. Yohimbine and raubasine carry on a competitive type antagonism on the noradrenaline effect. 4. On the thoracic aorta, yohimbine (pA2 = 6.83) and raubasine (pA2 = 7.21) act as competitive antagonists.