Lactate increases potassium secretion by perfused rat kidney.

The effect of exogenous metabolic substrates on K+ secretion was evaluated in the isolated perfused rat kidney in the presence of 2-deoxyglucose and 2-tetradecylglycidic acid to inhibit utilization of glucose and fatty acids from endogenous sources. L-Lactate (15 mM) added to the perfusion medium enhanced renal oxygen consumption (4.0 +/- 1.1 mumol X min-1 X g-1 vs. 2.0 +/- 1.0 without lactate) while decreasing fractional excretion of sodium (19.3 +/- 2.4% vs. 47.3 +/- 1.8). L-Lactate markedly increased the fractional excretion of K+ to 181 +/- 29% compared with 68 +/- 12% without lactate (P less than 0.001). The poorly metabolized isomer D-lactate did not alter these parameters. The addition of alpha-ketoglutarate only slightly increased K+ excretion. In the absence of metabolic inhibitors and in the presence of glucose (5 mM), L-lactate also increased K+ excretion significantly more than did D-lactate (108 +/- 19% vs. 69 +/- 11, P less than 0.02). At the end of 90 min of perfusion with L-lactate medium, K+ concentration in the perfusate dropped from 4.7 +/- 0.05 to 3.2 +/- 0.2 meq/liter (vs. 3.8 +/- 0.1 meq/liter with D-lactate, P less than 0.005) without differences in glomerular filtration rate or sodium excretion. L-Lactate appears to increase K+ secretion by preferential metabolic stimulation of the distal tubule, a process that may help in vivo to prevent hyperkalemia in lactic acidosis.