Vascular Renin-Like Activity and Blood Pressure

Plasma renin activity, reninlike activity present at the artery wall, pressor response to exogenous hog renin, renin half-life time, and renin-like activity present at the artery wall 1 hour after injection of renin were measured in conscious rats 1 month after inducing hypertension by renal artery constriction and contralateral nephrectomy (one-kidney hypertension). Plasma renin activity was higher but without statistical significance in one-kidney hypertensive rats when compared with normotensive or sham-operated animals. Renin-like activity present at the artery wall was significantly increased in hypertensive animals only when compared with one-kidney normotensive rats. Pressor responses to renin in one-kidney hypertensive and normotensive rats were of significantly longer duration than in sham-operated animals. The inactivation rate of exogenous renin followed a first-order reaction with a half-life of 6 minutes in sham-operated rats and of 12 minutes in one-kidney hypertensive and normotensive animals. Decreased inactivation of circulating renin could explain the protraction of the pressor response; however, the slope of the regression equation describing the inactivation of renin in all of the rats was steeper than the slope of the pressor response, indicating a dissociation between blood pressure and plasma renin activity. The renin-like activity present at the artery wall 1 hour after injection of renin was determined in the three groups; the arterial tissue of one-kidney hypertensive rats bound more circulating renin than that of normotensive rats and the latter more than that of sham-operated animals, suggesting the participation of this binding capacity in the protraction of the pressor response and in the maintenance of hypertension.