Effect of angiotensin II and glucocorticoids on plasma angiotensinogen concentration in the dog

The increase in plasma angiotensinogen concentration produced by angiotensin II infusion in the dog is accompanied by an increase in plasma corticosteroid concentration and is prevented by adrenalectomy. The present study was undertaken to test the possibility that the angiotensinogen response to angiotensin is mediated via an increase in glucocorticoid secretion. Infusion of angiotensin II (3-6 mug/h for 5 h) into the third cerebral ventricle of five dogs increased plasma corticosteroid concentration from 3.5+/-0.6 to 11.8+/-1.5 mug/dl (P less than 0.025) but did not increase plasma corticosteroid concentration from 2.7+/-0.4 to 7.8+/-1.5 mug/dl (P less than 0.05) but again failed to increase plasma angiotensinogen concentration. On the other hand, more prolonged glucocorticoid treatment with dexamethasone produced a significant increase in plasma angiotensinogen concentration within 24 h. Intravenous infusion of angiotensin II (50 mug/h for 5 h) in five acutely hypophysectomized dogs receiving a cortisol infusion caused only a small increase in plasma corticosteroid concentration (5.0+/-0.5 TO 6.9+/-0.6 mug/dl, P less than 0.02) but increased plasma angiotensinogen concentration from 967+/-122 to 1,358+/-204 ng/ml (P less than 0.02). These results indicate that although glucocorticoids can increase plasma angiotensinogen concentration, the angiotensinogen response to angiotensin II is not dependent on increased glucocorticoid secretion.