Effect of Injected Thyrotropic Hormone on thein VitroUptake and Metabolism of131I by Thyroid Glands of Fetal and Newborn Rats

Abstract

Intact thyroid gland lobes of fetal, newborn and adult rats, and slices prepared from glands of adult rats, all of which had been injected with identical doses of TSH in relation to body weight, were incubated in a Ringer-bicarbonate medium containing ¹³¹I, and their incorporation of the labeled iodine into iodoamino acids was compared. A distinct difference between the ¹³¹I metabolism of the intact lobe and slices of the adult rat thyroid gland was observed. This consisted of a greater uptake of the added 131I and its incorporation into DIT by the lobes. The finding that early after a TSH injection the ¹³¹I uptake by the incubated intact thyroid lobe of adult rat is diminished is confirmed. This was not observed in the experiments with slices. Under identical hormone treatments, the incubated thyroid glands of fetuses and newborn rats were much more responsive to injected TSH than were those of adult rats. A dual action of TSH on ¹³¹I metabolism by the incubated thyroid lobe of fetuses and newborn rats was found: (a) an initial one (30 min to 5 hr) in which only the disposition of the tissue’s ¹³¹I was affected; and (b) a later action (19-24 hr) in which uptake as well as internal disposition was involved. (Endocrinology75: 547, 1964)