Lactate gradients in the kidney of the dog

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Abstract
Previous studies have shown that the inner medulla of the antidiuretic kidney has a higher concentration of lactate than the renal cortex, blood, or urine and that medullary lactate rises even higher during osmotic diuresis. The present study was designed to ascertain whether a concentration gradient for lactate exists in the renal medulla and to explore changes in the gradient occurring as the result of osmotic diuresis. Hydropenic, anesthetized, curarized, ventilated dogs were subjected to a solute diuresis with mannitol, urea, or sodium chloride. When a steady state of diuresis was achieved the kidneys were quickly removed, frozen, and sections from the cortex, outer and inner medulla, and medullary tip were analyzed for water content, lactate, Na+, K+, and Cl-. In antidiuretic dogs, significant corticomedullary lactate sodium, and chloride concentration gradients were observed. The lactate gradient increased significantly during solute diuresis whereas the gradients for Na+ and Cl- fell. The results could not be explained by lactate present in the trapped urine or blood in the tissue. They are compatible with the view that some of the energy for Na+ transport in the loop of Henle is derived from glycolytic metabolism and that glycolysis is augmented during solute diuresis.

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