Role of glucocorticosteroid hormones on the levels of rat liver carbamoylphosphate synthase (ammonia) and arginase activity during ontogenesis.

In rats, hepatic carbamoylphosphate synthase (ammonia) and arginase activities are closely related during development. Activities increase sharply during the last 4 prenatal and first 4 postnatal days and during the 3rd postnatal week. Decreases are observed between 4 and 9 days after birth, and after weaning, during adolescence. During senescence activities increase again. Before birth, treatment and prednisolone is far less effective in increasing enzyme activities than during the first 2 postnatal weeks, when it seems to precipitate normal development of the 3rd postnatal week. In the 4th postnatal week the sensitivity to prednisolone treatment increases approximately 25-fold. During the 2nd postnatal week, dexamethasone proves to be more potent, on a molar base, than triamcinolone which is more potent than prednisolone and hydrocortisone. Increases in enzyme activities which are associated with increases in blood levels of glucocorticosteroids are also associated with 2- to 3-fold decreases in DNA content, i.e. with decreases in hepatocyte multiplication rate and increases in hepatocyte cell size. These phenomena may be sequelae of quantal cell cycles leading to changes in hormone response capacity or hormone response sensitivity.