Glucose homeostasis in fasted neonatal rats treated with high doses of L-thyroxine

A neo-T4 syndrome was induced by subcutaneous administration of high doses of L-thyroxine (T4) to neonatal rats. These doses produced important alterations in carbohydrate metabolism: hypoglycemia, hypoinsulinemia and increased levels of blood lactate, pyruvate and ketone bodies. T4-treated and control rats were subjected to fasting. In contrast to controls where glycemia decreased to 60% of basal values, in 11-day-old neo-T4 rats blood glucose levels decreased to only 90% of basal values. These different adaptations to fasting area discussed with regard to endocrine equilibrium in neo-T4 rats.