Modification of the Pressor Response to Sympathomimetic Amines by Acutely Administered Reserpine in Dogs

Using atropinized dogs under morphine and pentobarbital anesthesia, an overall study was conducted on blood pressure changes in response to sympathomimetic amines such as ephedrine, methamphetamine, tyramine, pheniprazine, epinephrine and norepinephrine after acute reserpinization.1) Pressor effects of ephedrine and related compounds were markedly augmented after acute reserpinization. The rate of rise was higher as the dose was decreased. Ephedrine and methamphetamine above 0.5 mg/kg caused i) a suppression of blood pressure rise despite reserpine administration or ii) a tendency to tachyphylaxis. However, reserpine administration somewhat temporarily suppresses the appearance of tachyphylaxis . When no control dose of these drugs was administered before reserpine, on the other hand, all of these drugs administered for the first time after reserpine markedly raised blood pressure. At a control dose tyramine had more intense pressor action than other drugs and administration of more than 0.5 mg/kg after reserpine may reduce the degree of blood pressure rise in some animals. Action of raising blood pressure of pheniprazine at a control dose was weaker than that of other drugs and the rise of blood pressure after reserpine was markedly accentuated, making the difference before and after reserpine more pronounced. The intensity of the rise of blood pressure through norepinephrine and epinephrine tended to decrease slightly after reserpine.2) The rate of the rise of blood pressure by ephedrine and related compounds in acutely reserpinized dogs revealed some suppression of ephedrine and methamphetamine action after adrenalectomy. In tyramine, the change in the rate of augmentation was not so pronounced. On the contrary, the rate of the rise of blood pressure by pheniprazine tended to increase.