Effect of sex hormones on oxalate-synthesizing enzymes in male and female rat livers

PURPOSE: We studied the effect of changes in sex hormones on oxalate metabolism in rats. MATERIALS AND METHODS: Adult male and female rats were administered a precursor of oxalate, and the relationship between dose and urinary oxalate was examined. Levels of sex hormones were varied in rats and glycolate oxidase (GO) and serine pyruvate aminotransferase (SPT) activities were measured under the conditions of being fed tap water or loading with 0.5% ethylene glycol. In addition, urinary oxalate excretion was evaluated. RESULTS: Ethylene glycol and glycolate increased urinary oxalate concentration in male rats dose-dependently but less in female rats. There was almost no change during glycine loading in either male or female rats. GO activity was significantly lower in intact female and gonadectomized male rats. SPT activity was slightly higher in the female than in the male controls. There were no differences in urinary oxalate excretions between male and female rats. During ethylene glycol loading, GO and SPT activities were similar to those with tap water intake. However, urinary oxalate excretion increased to two times the control value in male rats but only slightly increased in female rats. CONCLUSIONS: Sex-related differences exist in the metabolic conversion of glycolate to oxalate in rats, and GO activity is promoted by testosterone. Although difference in GO activity has no physiological effect on oxalate synthesis, GO activity affects urinary oxalate excretion during ethylene glycol loading. We could also conclude that estrogen decreases GO activity in male rats from our results.