Influence of Estradiol on Thyroid: Serum Radioiodide Concentration Ratios of Gonadectomized and Hypophysectomized Rats

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Abstract
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 ovariectomized females and is characterized by an almost immediate elevation without a preceding depression. (Endocrinology74: 680, 1964)

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