EFFECT OF METABOLIC-ACIDOSIS ON RENAL TUBULAR SODIUM HANDLING IN RATSAS DETERMINED BY LITHIUM CLEARANCE

Systemic metabolic acidosis is known to cause a decrease in salt and w ater reabsorption by the kidney. We have used renal lithium clearance to investigate the effect of chronic, NH4Cl-induced metabolic acidosis on the renal handling of Na+ in male Wistar-Hannover rats (200-250 g) . Chronic acidosis (pH 7.16 +/- 0.13) caused a sustained increase in r enal fractional Na+ excretion (267.9 +/- 36.4%), accompanied by an inc rease in fractional proximal (113.3 +/- 3.6%) and post-proximal (179.7 +/- 20.2%) Na+ and urinary K+ (163.4 +/- 5.6%) excretion when compare d to control and pair-fed rats. These differences occurred in spite of an unchanged creatinine clearance and Na+ filtered load. A lower fina l body weight was observed in the acidotic (232 +/- 4.6 g) and pair-fe d (225 +/- 3.6 g) rats compared to the controls (258 +/- 3.7 g). In co ntrast, there was a significant increase in the kidney weights of acid otic rats (1.73 +/- 0.05 g) compared to the other experimental groups (control, 1.46 +/- 0.05 g; pair-fed, 1.4 +/- 0.05 g). We suggest that altered renal Na+ and K+ handling in acidotic rats may result from a r eciprocal relationship between the level of metabolism in renal tubule s and ion transport.