Neonatal Thyroidal Hyperactivity

Introduction During the first few days of postnatal life, serum hormonal iodine values¹⁻³and triiodothyronine I 131 erythrocyte uptake⁴,⁵have 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 I¹³¹clearance⁶which 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 I¹³¹uptake were conducted by methods previously reported.⁶Radioiodine doses of 1μC were employed in the