Thyroid hormones and the precocious induction of hepatic glucokinase in the neonatal rat

1 Oral intubation of glucose is more effective than intraperitoneal injection in inducing the premature appearance of hepatic glucokinase in suckling rats. 2 The inducing effect of glucose is enhanced by treatment of the animals 12 h or more earlier with 1 pg triiodothyronine/g body weight. 3 Low but significant activities of glucokinase appear at the normal time of development in hypothyroid neonatal rats. Intubation of glucose into 13‐day‐old and 24‐day‐old hypothyroid rats results in the rapid appearance of glucokinase similar to that in normal animals treated likewise. 4 The enhancing effect of thyroid hormones on glucokinase induction by glucose does not necessarily mean that the normal postnatal increase in plasma thyroid hormones is essential for the normal appearance of glucokinase activity at the time of weaning. Other possible explanations are discussed.