INTERRELATION OF THE PITUITARY–THYROID SYSTEM AT BIRTH IN MAN

Abstract

Samples of cord blood derived from 105 normal babies after uncomplicated deliveries were assayed for thyroxine (T₄), tri-iodothyronine (T₃), reverse tri-iodothyronine (rT₃), throxinebinding globulin (TBG) and thyrotrophin (TSH). The values for T₃, rT₃ and TSH were log-normally distributed (geometric means 0·62 nmol/l, 3·28 nmol/l and 10·9 mu./l respectively) and those for T₄ and TBG were normally distributed (means 126 nmol/l and 13·7 mg/1). The data were systematically analysed and no evidence was obtained to suggest that the concentration of TSH, which varied widely, was regulated by any of the thyroid hormones alone or in combination. There was a direct relation between the concentrations of T₄ and T₃ in the cord blood at birth but not between either of these and rT₃. There is thus no evidence of a functional interdependence of the hypothalamic-pituitary-thyroid system in man at birth.