The pathogenesis of post-obstructive diuresis. The role of circulating natriuretic and diuretic factors, including urea.

To investigate the pathogenesis of post-obstructive diuresis, a state of functional "anuria" during ureteral obstruction was created in awake rats by (a) bilateral obstruction (BO); (b) unilateral obstruction and contralateral nephrectomy (UO-Nx); or (c) unilateral obstruction and continuous i.v. reinfusion of urine from the intact contralateral kidney (UO-reinf). These groups were compared with unilaterally obstructed (UO) and sham-operated control (sham) rats. After release of obstruction of 24 h duration, mean urine flows (V) and sodium excretion rates (UNaV) were significantly elevated above those of sham rats in BO, UO-Nx, and UO-reinf animals, but slightly decreased in UO rats. Glomerular filtration rates were comparably depressed in UO, BO, UO-Nx, and UO-reinf rats. These results suggest that post-obstructive diuresis is due to one or more circulating diuretic factors that are normally excreted in the urine, and which, when retained )as in BO or UO-Nx rats) or returned to the circulation (as in UO-reinf rats), exert a diuretic affect. In additional experiments, UO rats infused with urea exhibited post-obstructive diuresis, if extracellular volume contraction was prevented. This result suggests that urea may be an important diuretic factor in post-obstructive diuresis, but does not exclude possible roles for other humoral factors. The intact kidney of UO-reinf rats displayed a massive unilateral diuresis and natriuresis, further suggesting the presence of potent diuretic factors in the urine. A marked increase in the fractional excretion of glomerular filtrate (V/GFR) by the intact kidney suggests that this diuresis may be attributable, in part, to impaired proximal reabsorption.