Role of Sex Steroid Hormones in the Normal and Glucocorticosteroid Hormone-Induced Evolution of Carbamoylphosphate Synthase (Ammonia) and Arginase Activity in Rat Liver Ontogenesis

Abstract

The effects of sex steroid hormones on the developmental changes of carbamoylphosphate synthase and arginase activity, and DNA content in rat liver were investigated. After birth, administration of estradiol causes an increase in carbamoylphosphate synthase and arginase activity at high dosages only. Progesterone strongly inhibits or even reverses these stimulatory effects of estradiol. Administration of progesterone alone had no effects in the 1st postnatal week, a stimulatory effect in the 2nd postnatal week, and slightly inhibitory effects on enzyme activities thereafter. Testosterone hardly affected enzyme activities in the 1st 2 postnatal weeks and slightly decreased them from the 3rd postnatal week onwards. No differences in the response of either sex to these hormone treatments were observed. During the last 4 prenatal days and during the 1st postnatal week progesterone partially inhibited the prednisolone-induced enzyme accumulation and decrease in DNA content. Testosterone had such effects during the 1st 2 postnatal weeks. Comparison of these and previous experimental results with the developmental profiles of carbamoylphosphate synthase (ammonia) and arginase activity and DNA content on the one hand and with the developmental profile of steroid hormone levels on the other shows that only glucocorticosteroids influence enzyme activity and DNA content profiles, while progesterone and testosterone modulate the profiles by antagonizing the effects of glucocorticosteroids. No role for estrogens could be established.