Effect of metabolic acidosis on glucose reabsorption in rats with acute hyperglycemia

The rate of reabsorption of glucose in the kidney is a factor to consider with respect to the degree of hyperglycemia in poorly controlled diabetics. The rate of reabsorption of glucose in the proximal tubule is driven by the electrochemical gradient for sodium across the luminal membrane. This gradient in the proximal tubule is also used to reabsorb a number of other substances, quantitatively the most important being bicarbonate. We wished to explore the hypothesis that acidosis, by reducing the filtered load of bicarbonate and therefore the reabsorption of bicarbonate in the proximal tubule, might permit an increased rate of reabsorption of glucose. Hyperglycemia was induced in rats by the infusion of hypertonic glucose. Reabsorption of glucose was measured by clearance methods and factored for glomerular filtration rate (GFR), which has a direct effect on the reabsorption of glucose. The reabsorption of glucose was increased in the kidney when the reabsorption of bicarbonate in the proximal tubule was decreased by either HCl-induced acidosis or the administration of a carbonic anhydrase inhibitor. This effect was independent of a change in GFR and the fractional excretion of Na, factors that may also lead to changes in the reabsorption of glucose by the kidney.