Role of Thyrotropic Hormone in Iodine Metabolism of Embryonic Rat Thyroid Glands in Organ Culture

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Abstract
Embryonic thyroid glands of 16-16.5-day-old and 17-17.5-day-old embryonic rats were cultured for 4 days in 4 different media: a synthetic medium; the synthetic medium to which TSH was added; the synthetic medium to which serum from hypophysectomized rats was added; and the synthetic medium to which both serum from hypophysectomized rats and TSH were added. 2. Thyroid explants of 16-16.5-day-old embryonic rats made no significant use of added 131I when cultured in the completely synthetic medium. The addition of serum prepared from the blood of hypophysectomized rats increased somewhat the capacity of the explants to metabolize m I. The addition of TSH had a significant effect on the functional activity of the embryonic thyroid explanted into culture either in the synthetic medium or in the synthetic medium to which serum had been added. In the former, addition of the TSH enhanced utilization of the added 131I, and only in the presence of TSH was the formation of labeled T4 observed. 3. When embryonic glands of 17-17.5-dayold rats were cultured in the synthetic medium, the 131I that entered the explant was incorporated principally into protein-bound MIT and DIT (MIT-131I/DIT-131I =about 10), and the amounts of labeled T4 formed were very low. The addition of serum greatly improved the uptake and metabolism of 131I by the explants. Addition of TSH to the synthetic medium accelerated the conversion of MIT to DIT as well as coupling of DIT, and thus formation of thyroid hormones. Addition of TSH to the serum-containing medium improved organification of the 131I concentrated by the explant, which was reflected mainly in its increased incorporation into T4. 4. The increased 131I utilization observed upon addition of serum to the culture medium was most clearly shown in experiments with thyroid glands of 17-17.5-day-old embryonic rats. This effect cannot be ascribed to TSH because the serum was prepared from the blood of rats that had been hypophysectomized 6 months previously. (Endocrinology76: 35, 1965)