Studies on the development of ornithine–keto acid aminotransferase activity in rat liver

1. During the normal development of the rat, the specific activity of liver ornithine–keto acid aminotransferase exhibits a transient elevation around term, and subsequently increases to adult activity levels during the third postnatal week. 2. The synthetic glucocorticoid triamcinolone, administered as a single injection, produces a marked elevation of the ornithine–keto acid aminotransferase activity within 24hr. if given postnatally before the natural increase in ornithine–keto acid aminotransferase activity has occurred. In foetal and adult animals, triamcinolone does not induce any increase in this enzyme activity. 3. The repeated administration of puromycin completely prevents the rise in ornithine–keto acid aminotransferase activity that follows triamcinolone administration. 4. If adult rats are fed with a protein-free carbohydrate diet, or one free of arginine, the ornithine–keto acid aminotransferase activity diminishes to a fraction of the normal. When such diets are given, a single injection of triamcinolone does not increase the enzyme activity within 24hr. 5. Partial hepatectomy, and repeated injections of growth hormone, depress the ornithine–keto acid aminotransferase activity in adult rats. 6. The findings are discussed in relation to the mechanisms concerned with developmental and adaptive changes in enzyme activities in the liver.