[Interactions between alpha 1, alpha 2 and beta receptors in the blood pressure effects of adrenaline and noradrenaline in the dog].

In anaesthetized dog, the adrenaline induced hypertension is reversed by both alpha 1- and alpha 2-adrenoceptor blocking agents such as AR-C 239 and yohimbine. After alpha 1 or alpha 2 and beta-blockade, adrenaline induced again an increase in blood pressure. This hypertensive effect was suppressed by an alpha 2-adrenoceptor blocking agent when an alpha 1-adrenoceptor blocking was responsible for the reversal of adrenaline-induced hypertension, and conversely. After beta-blockade, both alpha 1- and alpha 2-adrenoceptor blockade is necessary for suppressing any tensional effect of adrenaline. On the other hand, alpha 1- and alpha 2-adrenoceptor blockade are both required to prevent beta-blockade from restoring adrenaline hypertensive effect. Similar effects were observed wih noradrenaline. In fact, only a significant decrease of the noradrenaline-induced hypertension was observed after each alpha-blocker. Both alpha 1- and alpha 2-adrenoceptor blocking agent also significantly inhibited the hypertension induced by noradrenaline. For completely suppressing the effect of noradrenaline on blood pressure, a combination of alpha 1, alpha 2 and beta-blockade is necessary. These results are compatible with a stimulation by adrenaline and noradrenaline of both alpha 1- and alpha 2-adrenoceptors to produce increase in blood pressure.