Umbilical cord cutting triggers hypertriiodothyroninemia and nonshivering thermogenesis in the newborn lamb.

The present studies in the newborn sheep were undertaken to further clarify the mechanism or mechanisms for the early increases in serum thyroid hormone concentrations in the newborn as well as the significance of these changes to newborn nonshivering thermogenesis. Six groups of animals were studied to determine the influence of neonatal cooling, cord cutting, and the effects of thyrotropin-releasing hormone (TRH) and triiodothyronine (T3) injections. Group I newborns were delivered into room air with immediate cord cutting. Group II animals were delivered into room air and cord cutting was delayed 60 min. Group II animals were delivered into a 39 degrees water bath and maintained for 60 min with the umbilical cord intact; the cord was cut at the time of removal from the water bath...