Neonatal Thyroidal Hyperactivity: Response to Cooling

Introduction  During the first few days of postnatal life, serum hormonal iodine values ^1-3 and triiodothyronine I 131 erythrocyte uptake ^4,5 have been shown to increase significantly. In a previous report we have shown that these increases occur in association with an early (10-24 hours of age) high rate of thyroid I¹³¹ clearance ⁶ which suggests that this neonatal thyroidal hyperactivity may be the result of stimulation by thyroid stimulating hormone (TSH) during the early hours of postnatal life.The present studies report further investigations of thyroid radioiodine uptake and studies of the influence of neonatal cooling and exogenous adrenal cortical steroid on neonatal thyroidal hyperactivity.

Methods  Protein-bound iodine (PBI) determinations were conducted at Bioscience Laboratories by Barker's alkaline ashing technique. Fractional thyroid radioiodine clearance measurements (k₁)* and 24-hour thyroid I¹³¹ uptake were conducted by methods previously reported.⁶ Radioiodine doses of 1μC were employed in the