[The mechanisms of exercise-induced proteinuria--relationship between urinary excretion of proteins and lactate after exhaustive exercise].

Exercise-induced proteinuria is of the mixed glomerular-tubular type and has been thought to be due to increased glomerular permeability to macromolecular proteins in response to activation of the renin-angiotensin system and catecholamines and a reduction in renal hemodynamics. The excretion of the tubular type of proteins, however, can't be explained by the above mechanism. Two groups, consisting of subjects with the highest (H-alb, n = 20) and the lowest (L-alb, n = 20) excretion of albumin 30 min after exhaustive exercise were selected from a total of 69 normal male participants. No differences in VO2max, maxHR, changes in plasma angiotensin II, catecholamines, urine volume, or Ccr following exercise were observed between the two groups. The increase in blood lactate concentration immediately after exercise, increases in urinary excretion of lactate, pyruvate, alpha 1 M, beta 2 M, albumin and decrease in Cl- excretion 30 min after exercise in the H-alb group were significantly greater than in the L-alb group. The greater the urinary excretion of lactate and pyruvate, the greater the excretion of albumin, alpha 1M and beta 2M, and the less the urinary excretion of Cl-. The coefficient of correlation between the urinary excretion of lactate and beta 2M was 0.757, and between urinary excretion of albumin and beta 2M, 0.756 (p less than 0.001). These results suggest that exercise-induced organic acids and/or decrease in renal circulatory pH caused by organic acids may alter renal glomerular permeability and inhibit renal tubular reabsorption of low molecular weight proteins (alpha 1M, beta 2M). The permeability of the glomerular basement membrane (GBM) to macromolecular proteins may be altered by a reduction in the charge barrier of the GBM, which may be caused by the over-production of organic acids and a lower pH.