Renal tubular transport of water, solute, and PAH in rats loaded with isotonic saline

Abstract

Renal tubular transport of water, osmotically active solute, and PAH were studied with micropuncture methods in anesthetized rats loaded with a volume of 0.9% sodium chloride solution equivalent to 10% of their body weight. Inulin clearance and urine flow were greatly elevated above values in nondiuretic animals, but there was little change in PAH clearance. F/P inulin-C 14 OOH ratios indicated that 42% of the filtered water and solute was reabsorbed along the proximal convolution, a lower fraction than is found in nondiuretic and hypertonic saline-loaded rats. This indicates that the rate of solute and water reabsorption in the proximal tubule did not increase in proportion to the increased filtered load, and it was, in fact, similar to that in nondiuretic rats. Intravenous administration of vasopressin and aldosterone had no demonstrable effects on solute or water reabsorption. F/P PAH/inulin ratios demonstrated that PAH secretion occurred along the proximal tubule, but probably in no other portion of the nephron.