Thyrotropin secretory response to thyrotropin-releasing hormone in the hypothyroid perinatal rat: further evidence of thyrotroph independence of the hypothalamus during early ontogenesis.

Abstract

Propylthiouracil fed to pregnant rats for the last week of gestation to induce maternal and fetal hypothyroidism induced a 3-fold rise in plasma TSH concentration in the newborn pups compared to a 4-fold rise in their mothers. Subcutaneous administration of 1 ng/g BW TRH caused a greater rise in plasma TSH in the hypothyroid pups than in their mothers. These results, in combination with published data, indicate that the apparent independence of pituitary-thyroid function from TRH control during early ontogenesis in the rat is primarily due to delayed maturation of the hypothalamic TRH system.