Mechanism of exaggerated diuresis in spontaneously hypertensive rats

Abstract

The mechanism of exaggerated diuresis and natriuresis was studied in spontaneously hypertensive rats (SHR) and control normotensive rats (WKY), by renal clearance and micropuncture techniques. During the hydropenic control and the volume-expansion experimental periods, absolute and fractional H2O and Na excretion were greater in SHR than in WKY. Although fractional and absolute H2O and Na reabsorption were similar along the proximal convolution in SHR and WKY, fractional and absolute H2O reabsorption in Henle''s loop was less in SHR than in WKY. Hydrostatic and colloid osmotic pressures in the cortical peritubular microvasculature were similar in WKY and SHR. Acute normalization of renal perfusion pressure by aortic constriction reversed the exaggerated diuresis and natriuresis in SHR by halving the filtered load of H2O and Na; whole kidney and single nephron glomerular filtration rates and blood flows decreased by 50%. Exaggerated diuresis and natriuresis of the spontaneously hypertensive rat is apparently caused by decreased reabsorption in the loop in Henle. The mechanism of this decreased reabsorption in the loop of Henle cannot be explained by alterations in the measured physical forces in the renal cortical microvasculature.