RESUMEN
Systemic metabolic acidosis is known to cause a decrease in salt and water 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 ñ 0.13) caused a sustained increase in renal fractional Na+ excretion (267.9 ñ 36.4 per cent), accompanied by an increase in fractional proximal (113.3 ñ 3.6 per cent) and post-proximal (179.7 ñ 20.2 per cent) Na+ and urinary K+ (163.4 ñ 5.6 per cent) excretion when compared to control and pair-fed rats. These differences occurred in spite of an unchanged creatinine clearance and Na+ filtered load. A lower final body weight was observed in the acidotic (232 ñ 4.6 g) and pair-fed (225 ñ 3.6 g) rats compared to the controls (258 ñ 3.7 g). In contrast, there was a significant increase in the kidney weights of acidotic rats (1.73 ñ 0.05 g) compared to the other experimental groups (control, 1.46 ñ 0.05 g; pair-fed, 1.4 ñ 0.05 g). We suggest that altered renal Na+ and K+ handling in acidotic rats may result from a reciprocal relationship between the level of metabolism in renal tubules and ion transport.