Abstract
The aim of the present experiment was to investigate effects of ephedrine and reserpine, administered in vivo, on responses of dog isolated arterial strips to adrenergic drugs, and to study a possible mechanism involved in the reversal of blood pressure responses to dopamine. Dose-dependent contractile responses to adrenaline (A), dopamine (DA) and ephedrine (ED) were depressed in the femoral strips isolated from the ED-treated dogs as compared with those isolated from the untreated dogs. Those to noradrenaline (NA) were potentiated in low concentration and inhibited in high concentration, though those to tyramine (TY) were not altered. Relaxing and contractile responses to isoprenaline (IP) were inhibited. DA did not induce a relaxing effect but a contractile one even in the strips brought to a state of moderate tone with ED or phelypressin. In the strips isolated from the reserpine-treated dogs, contractile responses were to some extent potentiated by NA, A and DA, and significantly by ED, while those to TY were inhibited. Relaxing responses to IP were reduced and contractile responses potentiated. In the strips extirpated from the reserpine and ED-treated dogs, contractile responses to NA and A were potentiated in low concentration and inhibited in high concentration. Those to TY were inhibited in low concentration and tended to be potentiated in high concentration whereas those to DA and ED were not affected. Dose-dependent relaxing effects of DA in the dog renal and mesenteric strips contracted previously by KCl after phenoxy-benzamine were attenuated by treatment with ephedrine in vivo. The results suggested that the dopamine reversal in the blood pressure may be mainly due to actions other than its peripheral effect on the blood vessels.
