Stimulation of angiotensinogen production: a dose-related effect of angiotensin II in the conscious dog.

The hypothesis that angiotensin II (AII) provides a positive feedback stimulus for production of angiotensinogen was examined in conscious dogs. AII was infused intravenously for 24 h at 5, 20, and 50 ng x kg-1 x min-1 and blood pressure, plasma renin activity (PRA), and the concentrations of AII, angiotensinogen, corticosteroids, and total protein in plasma were measured 0, 2, 4, and 24 h after the start of infusion. In addition, the liver content of angiotensinogen and the release of angiotensinogen by liver slices in vitro were measured after the 24-h sampling period. AII infusion increased blood pressure in a dose-related manner. PRA was markedly decreased by all doses of AII. Plasma corticosteroids were increased only at the highest dose of AII and did not bear any relationship to changes in the concentration of angiotensinogen. Plasma protein concentration and hematocrit were unchanged. Plasma angiotensinogen concentration was unchanged at 2 and 4 h but was increased significantly at 24 h by the two highest doses of AII. A linear relationship was found between the dose of AII and plasma angiotensinogen concentration, the liver content of angiotensinogen, and the release from liver slices during a 2-h incubation. These results provide further evidence that AII has a role in angiotensinogen production but suggest that it is of minor importance in physiological conditions.