INFLUENCE OF ESTRADIOL ON THYROID: SERUM RADIOIODIDE CONCENTRATION RATIOS OF GONADECTOMIZED AND HYPOPHYSECTOMIZED RATS.

The administration to ovariectomized female rats of estradiol benzoate for 3 consecutive days produces a significant elevation of thyroid:serum radioiodide concentration ratios (T:S) which is apparently not dependent upon the dosage employed in the range between 1 and 250 ng. Similar observations of enhanced thyroidal iodide concentrating activity in estrogen-treated hypophysectomized animals suggest that the stimulatory effect may be one which does not require mediation by pituitary thyrotrophin. The temporal response of the T:S ratios of ovariectomized female rats to a single injection of estradiol is characterized by an initial pituitary-dependent depression that is most marked 18 hr following injection. There is a subsequent elevation in concentrating activity that is maximal at 48–60 hr and that can also be observed in hypophysectomized-ovariectomized animals. The temporal response of T:S ratios of castrated male rats to a single injection of estradiol differs fundamentally from that of ovariectomize...