Hyperinsulinemia and the aldosterone and pressor responses to angiotensin II.

To determine whether hyperinsulinemia alters angiotensin II-mediated aldosterone secretion, the increase in plasma aldosterone after intravenous angiotensin II (5, 10, and 20 ng/kg/min for 15 minutes each) was measured before and after euglycemic hyperinsulinemia in seven chronically instrumented dogs. In a random sequence on 4 successive days, dogs received either 0, 2, 4, or 8 milliunits/kg/min insulin. Euglycemic hyperinsulinemia, at all insulin doses, resulted in a significantly greater (p less than 0.01) change in the angiotensin II-stimulated increments of plasma aldosterone than was observed when angiotensin II was administered alone. However, there was no dose-dependence of insulin's effect on angiotensin II-stimulated aldosterone. The effect of weight gain on the angiotensin II response was also evaluated in five dogs. After weight gain, euglycemic hyperinsulinemia augmented angiotensin II-stimulated aldosterone to the same magnitude that was observed before weight gain. Possible mechanisms whereby insulin could increase angiotensin II-stimulated aldosterone production include: increased intracellular potassium, reduced plasma free fatty acids, and a direct action of insulin to induce increased adrenal steroidogenesis. In addition to altering the angiotensin II-aldosterone dose-response curve, hyperinsulinemia also increased the pressor action of angiotensin II. In contrast to the angiotensin II-aldosterone response, progressive hyperinsulinemia resulted in a progressive increase in the pressor response to angiotensin II. The increased pressor response is probably due to an increased activation of the sympathetic nervous system by insulin.