EFFECTS OF SALINE AND MANNITOL ON RENIN AND DISTAL TUBULE NA IN RATS

The purpose of these experiments was to investigate the relationship between renin secretion (the product of renal plasma flow and renal venous minus arterial plasma renin) and distal tubular Na+ concentration and load (the product of Na+ concentration and tubular fluid flow rate) in pentobarbital-anesthetized rats. Induction of saline diuresis decreased renin secretion (from 274 ± 82 to 56 ± 18 ng/hr per min per kg, n=6 rats, P<0.03) and increased Na+ load (from 494 ± 40 to 1179 ± 181 pEq min, n=13 tubules, P<0.004). Induction of mannitol diuresis also decreased renin secretion (from 226 ± 62 to 21 ± 12 ng/hr per min per kg, n=6 rats, P<0.03) and increased Na+ load (from 479 ± 68 to 969 ± 147 pEq/min, n=13 tubules, P<0.004). Na+ concentration was increased by induction of saline diuresis (from 59 ± 2 to 79 ± 5 mEq/liter, P<0.004) and decreased by induction of mannitol diuresis (from 66 ± 5 to 49 ± 4 mEq/liter, P<0.004). Na+ concentration, Na+ load, and renin secretion rate were stable over time in a third group of rats (controls). The acute changes elicited by induction of osmotic diuresis were not consistent with a relation between Na+ concentration and renin secretion, but these changes were consistent with a reciprocal relation between Na+ load and renin secretion.