Neonatal thyroid function and anaesthesia

Thyroid function in the neonate and its response to hexobarbitone anaesthesia were studied in newborn Wistar rats between 24 h and 42 days old. 14C-labelled mixed with unlabelled hexobarbitone was injected i.p. in anaesthetic concentrations. Serum T3, reverse T3 (rT3) and T4 and serum and whole brain hexobarbitone concentrations were measured on wakening. A decrease in serum T3 and rT3 and an increase in T4 concentrations were observed after hexobarbitone at 21 and 30 days. This appears to be a critical period in the neonatal rat. A significant negative correlation was found between the changes in serum thyroid hormone concentrations and whole-brain concentrations of hexobarbitone in 30-day-old male rats. It is suggested that similar effects may occur in the human fetus or neonate subjected to anaesthesia.