Chronic hyperinsulinemia and blood pressure regulation.

The aims of this study were to determine whether chronic hyperinsulinemia, comparable to that found in obese hypertensives, elevates mean arterial pressure (MAP) or potentiates the hypertensive effects of angiotensin II (ANG II). Studies were conducted in conscious dogs with kidney mass reduced by 70% in order to increase their susceptibility to hypertensive stimuli. Insulin infusion (0.5 or 1.0 mU.kg-1.min-1 iv) for 7 days with plasma glucose held constant raised plasma insulin more than fivefold but did not increase MAP in four dogs on 138 meq/day Na intake. In seven dogs maintained on a high Na intake (319 meq/day), insulin infusion (1.0 mU.kg-1.min-1) for 28 days raised fasting insulin from 9.8 +/- 1.5 to 56-78 microU/ml but did not increase MAP, which averaged 106 +/- 2 mmHg during control and 102 +/- 2 mmHg during 28 days of insulin infusion. Insulin caused transient sodium and potassium retention followed by renal "escape" that was associated with increased glomerular filtration rate (12-27%). Plasma renin activity and plasma aldosterone were not altered by insulin. In five dogs infused with ANG II (2.0 ng.kg-1.min-1) to cause mild hypertension, insulin infusion (1.0 mU.kg-1.min-1) for 6-28 days did not increase MAP further. Thus chronic hyperinsulinemia did not elevate MAP, even when kidney mass was reduced, and did not potentiate the hypertensive effects of ANG II. These findings suggest that additional factors besides hyperinsulinemia per se are responsible for obesity-associated hypertension.