Patterns of nephron perfusion in acute and chronic hydronephrosis.

Abstract

The effects of acute and chronic hydronephrosis on renal function were investigated and compared to those of renal arterial constriction during water and hypotonic saline diuresis. In acute hydronephrosis there was a reduction in urinary Na concentration, Na excretion, and free water clearance (CH2O) per 100 ml glomerular filtration rate (GFR). The urinary osmolality was higher on the hydronephrotic side than on the control side during water diuresis and fell to below that of the control side during hypotonic saline diuresis. This pattern was similar to that of renal arterial constriction and, therefore, was due to distal nephron underperfusion. Chronic hydronephrosis resulted in a markedly different pattern characterized by an increase in urinary solute concentration, urinary Na concentration, and Na excretion; CH2O was decreased, whereas CH2O /100 ml GFR was increased. This pattern is best explained by a combination of reduced renal mass with overperfusion of residual nephrons as a result of increased filtration and diminished fractional reabsorption in the proximal nephron. Reduced back-diffusion of free water in the distal nephron may also contribute to the increased fractional excretion of water.