Renal excretion of lactic acid in the dog.

DUES, FEDERICO, GUADALUPE RAMOS, ESTHER AVELAR, AND MTGUEL LENNHOFF. Renal excretion of lactic acid in the dog. Am.J. Physiol. 216(l): 106-l 11. 1969.-The renal excretion of lactic acid was studied under different conditions in mongrel dogs, Previous reports that tubular reabsorption of lactic acid is rate limited were confirmed during experiments with rapid intravenous Na-lactate loading. Lactic acid-to-creatinine clearance ratios did not decrease below 2-3 y0 even when the filtered load of the acid was decreased to about 3074 of normal. Lactic acid excretion was urine flow dependent at low filtered loads, Osmotic diuresis increased fractional excretion of lactic acid. Extracellular fluid expansion with isotonic saline increased lactic acid excretion more than was expected from the levels of urine flow attained. Stop-flow studies showed that lactic acid was reabsorbed against a concentration gradient in “proximal samples.” It was concluded that lactic acid is actively reabsorbed in the proximal tubule, that its transport is rate limited, and that it is either incompletely reabsorbed at low filtered loads or partially secreted at a distal site of the nephron.