Initiation by Glucagon of the Premature Development of Tyrosine Aminotransferase, Serine Dehydratase, and Glucose-6-Phosphatase in Fetal Rat Liver

The explosive accumulation of tyrosine aminotransferase that normally occurs in rats at birth has been brought about prematurely by a single administration of glucagon to fetuses. Serine dehydratase is also found to accumulate normally after birth, but glucagon initiates its formation prenatally. The glucose-6-phosphatase activity of liver, which begins to develop just before birth, has been prematurely increased in fetuses by glucagon. The administration of hydrocortisone is without effect on the prenatal development of these three enzymes. The results suggest that glucagon may exert an important physiological function in the rat during the time of major developmental change in carbohydrate metabolism. The administration of glucose inhibits the early postnatal accumulation of tyrosine aminotransferase and serine dehydratase during the first 6 to 8 hours after birth. The results are consistent with the possibility that under normal conditions the decrease in blood glucose, upon cessation of the placental supply at birth, stimulates the secretion of glucagon, which then triggers the formation of tyrosine aminotransferase and serine dehydratase.