Effects of Sex Hormones on Three Glucocorticoid-Inducible Enzymes Concerned with Amino Acid Metabolism in Rat Liver

Abstract

The activities of three glucocorticoid-inducible enzymes, tryptophan oxygenase, tyrosine aminotransferase and alanine aminotransferase were significantly increased in the livers of female Sprague-Dawley rats by treatment with 10 ng estradiol benzoate daily for 14 days. Although estrogen-treated, adrenalectomised females did not show the same marked increases in tryptophan oxygenase and tyrosine aminotransferase, nevertheless the levels of these enzymes were higher than those of the adrenalectomised controls, whereas alanine aminotransferase was not affected by estrogens after adrenalectomy. It is suggested that the presence of adrenocorticosteroids is necessary for the full expression of the effect of estrogen upon tryptophan oxygenase, and tyrosine aminotransferase, and for the induction of alanine aminotransferase. Tryptophan oxygenase was reduced by ovariectomy or testosterone propionate injection, as well as by adrenalectomy. Untreated, intact male rats had significantly lower tryptophan oxygenase levels than intact female controls, but higher activities of tyrosine aminotransferase. Estradiol benzoatetreated intact males showed proportionately similar elevations of tryptophan oxygenase to those obtained in correspondingly treated female rats. Orchidectomy did not affect tryptophan oxygenase, but the increase in enzyme activity in orchidectomised males treated with estradiol was signifi- cantly higher than the response in intact males, and similar to that observed in intact female animals. (Endocrinology89: 1250, 1971)