Isotonic Saline Diuresis and Urinary Concentrating Ability in Renal Hypertensive Rats

Abstract

In rats made hypertensive by constricting one renal artery, the ‘clamped’ kidney could not elaborate a maximally concentrated urine after dehydration and under the influence of exogenous vasopressin. The diuretic response to the intravenous infusion of 0.86 ± 0.04 ml/kg min of 0.15 M NaCl solution was smaller in the ‘clamped’ than in a normal kidney: the urinary sodium and potassium concentrations were very low. The functional changes observed were already present a few hours after ‘clamping’ and, thus, preceded the development of hypertension and changes in renal renin concentration. In the ‘undamped’ kidney of the renal hypertensive rat salt and water were excreted 25 to 30% more rapidly than in a normal kidney at high rates of intravenous saline infusion. In intact renal hypertensive rats receiving intravenous saline at different rates, GFR (C_In) and salt water excretion rates were the same as in normal controls. The enhanced diuretic response to oral saline loads must, therefore, be ascribed mainly to extrarenal changes.