[Control of glycogen biosynthesis in fetal rat liver]

We have studied through the late foetal period of the rat, the evolution of two enzymes involved in glycogen metabolism of the liver : UDPG glycogen synthetase (a and b forms) and branching enzyme. The activities were measured during the development of normal foetuses and of foetuses experimentally deprived of corticosteroids. In normal foetus the activity of glycogen synthetase and the branching enzyme increased progressively between days 18 and 21 ; but the percentage of glycogen synthetase a increased promptly between days 18 and 19. This variation coincides with the beginning of glycogen accumulation in the liver. In foetuses submitted to corticosteroid shortage, the activity of each enzyme, and the amount of glycogen in the liver, were reduced at term. Cortisol given to the decapited foetus restores subnormal glycogen storage and normal activity of branching enzyme. The activity of synthetase a was slightly increased but remained very low ; only synthetase b was restored to normal. It seems that there is no relationship between the synthesis of glycogen, in the foetal rat liver, and the activity of synthetase a.