MALEATE EFFECTS ON KIDNEY PEPTIDASES AND PROTEINURIA OF MALE AND FEMALE RATS - HISTOCHEMICAL AND BIOCHEMICAL-STUDIES

The effects of maleate on membrane-bound and lysosomal peptidases were studied histochemically in the kidney and biochemically in the kidney and the urine of male and female rats 6 h after the administration of 2 different doses of sodium maleate (150 and 300 mg/kg body weight). The proteinuria of experimental animals was electrophoretically analyzed to detect maleate-induced alterations in the urinary protein composition. The histochemistry of the brush-border peptidases (aminopeptidase A, .gamma.-glutamyltransferase) showed dose-dependent maleate effects in the late pars convoluta and the pars recta of the proximal tubule (blurring of the brush-border enzyme reaction pattern). The female animals were more severely affected by both maleate doses. After maleate treatment, enzyme-activity measurements in the kidney homogenate supernatant and urine indicated dose-dependent structural destruction of the proximal tubule, especially of brush-border membranes, and revealed an increase in enzyme excretion. Both the maleate-induced enzyme excretion and proteinuria were more pronouncedly increased in females than in males. Electrophoretic analysis of urinary proteins revealed alterations in the urinary-protein composition after maleate treatment, which favored the excretion of proteins with a MW higher than 20,000 daltons. Sex-related differences in the maleate effects were demonstrated. Maleate may cause alterations in the brush-border membranes and, especially at higher doses, results in cellular destruction selectively in the late proximal tubule of rat kidneys. Selectivity was encountered in the maleate effects on urinary-protein composition, suggesting that the tubular alterations lead to an inhibition of the reabsorption of mainly high-MW proteins. Although the nature of the effects was independent of sex, it appears that females are less well protected against tubular damage caused by maleate.