Release of Adrenal Catecholamines by Angiotensin II

Several recent investigations have presented indirect evidence that angiotensin stimulates the release of adrenal medullary catecholamines. The following work was undertaken in an attempt to show in vivo angiotensin stimulation of the adrenal medulla by analysis of plasma catecholamines. Mongrel dogs, anesthetized with pentobarbital, were infused for 10 min with doses of 0.025, 0.05, and 0.1 µg per kg per min of angiotensin or injected with single doses of 0.5, 1.0 and 2.0 µg per kg. Blood samples were taken from the inferior vena cava (above the outflow from the adrenal veins) at the peak of the pressor responses to single doses or during and after the infusions. The samples were fluorometrically analyzed for epinephrine and norepinephrine. It was found that angiotensin produced an increase in circulating catecholamines. Epinephrine was significantly increased by infusions of 0.05 and 0.1 µg per kg per min and all three injected doses. Plasma norepinephrine was significantly increased also except with the 0.5 µg per kg injected dose of angiotensin. Angiotensin infusion of 0.025 µg per kg per min did not cause a detectable change in circulating catecholamine levels. In the infusion experiments, norepinephrine was more transiently increased than epinephrine. These results show that various pressor doses of angiotensin stimulate release of adrenal catecholamines.