The Effects of Age and Sex on Glycolic Acid Metabolism in Rats 1

Abstract

On a diet free of exogenous glycolic acid, male rats excrete more urinary oxalic acid than females do; a diet containing 2% glycolic acid produces hyperoxaluria in male rats, but not in females (1). In addition, glycolic acid is more toxic to male rats than to females (2). It has been suggested that these findings are related to the higher liver level of glycolic acid oxidase in adult male rats, apparently the result of enzyme induction by testosterone (3, 4).

Glycolic acid oxidase catalyzes the conversion of glycolic acid to glyoxylic acid (5). Several enzymes, among them glycolic acid oxidase, can catalyze the further oxidation of glyoxylic acid to oxalic acid (6, 7). An important alternate fate of the intermediate, glyoxylic acid, is transamination to glycine (8).

If the greater oxalic acid excretion of male rats, compared to females, is the result of higher liver levels of glycolic acid oxidase one might also expect a sex difference in the conversion of glycolic acid to glycine when increased amounts of glyoxylic acid become available for transamination as well as for further oxidation to oxalic acid. If glycolic acid oxidase does not catalyze the rate limiting reaction in the oxidation of glycolate to oxalate, the increased activity of this enzyme may not be a cause of the greater oxalate excretion in male rats compared to females.

This study was done to determine the effects of age and sex on the conversion of glycolic acid to glycine and to oxalic acid in rats in vivo.

Methods. Male and female rats of the Wistar strain were weaned at 3 weeks of age and fed the following diet ad libitum: (%) cornmeal, 42.1; skim milk, 18.4; linseed meal, 12.0; wheat germ, 7.5; yeast (unirradiated), 7.1; crude casein, 3.8; alfalfa meal, 1.5; iodized NaCl, 0.4; salt mixture of CaCO₃ plus trace elements, 0.4; irradiated yeast plus calcium pantothenate, 0.4; Wesson oil, 6.4. Each kilogram of irradiated yeast contained 6 g of calcium pantothenate.