The Developmental Formation of Liver Glucose 6-Phosphatase and Reduced Nicotinamide Adenine Dinucleotide Phosphate Dehydrogenase in Fetal Rats Treated with Thyroxine

Abstract

Abstract Enzyme formation during differentiation was studied by administering hormones to individual fetal rats in utero and comparing them with their untreated mates. Thyroxine raises considerably the levels of glucose 6-phosphatase and NADPH: cytochrome c oxidoreductase in fetal livers: within 5 and 24 hours, respectively, both enzymes reach approximately half of their adult levels. Glucagon has a similar effect on glucose 6-phosphatase but does not affect NADPH dehydrogenase, whereas tyrosine aminotransferase, the synthesis of which can be prematurely initiated by glucagon, is unaffected by thyroxine. Hydrocortisone acetate does not increase the level of any of these enzymes studied in fetal liver; it causes a small decrease in glucose 6-phosphatase. The different responses of the three enzymes to the experimental stimuli are in accord with their different developmental patterns. Fetal thyroid hormone is most probably the immediate cause for the first appearance of liver glucose 6-phosphatase and NADPH dehydrogenase during late gestation. The second upsurge of glucose 6-phosphatase activity and the first appearance of tyrosine aminotransferase are conditioned by the early postnatal secretion of glucagon. The results emphasize the plasticity of the developmental formation of enzymes; the role of fetal endocrine function in this aspect of differentiation may be approached by experimentally induced changes in the enzyme profile.