EFFECTS OF RETINOIDS ON IODINE-METABOLISM IN ISOLATED RAT-THYROID FOLLICLES

Isolated rat thyroid follicles in suspension culture were used as a model system for an investigation of the effect of retinol and retinoic acid on labelled iodine metabolism in a thyroid in vitro. The 4 hour I-125 uptake values by the isolated follicles ranged from 0.30% to 3.6% of the total labelled iodide added to the medium without thyrotropin (TSH) and from 10.2% to 18.3% with 0.5 mU/ml of TSH. The half life of the labelled iodine released from the isolated follicles cultured in the presence of TSH was about 16 hours. Although 10(-6) M retinol slightly decreased the labelled iodide uptake and organification, retinol had no effect on labelled iodine released from isolated follicles. However, 10(-9) to 10(-7) M retinoic acid markedly decreased the 4 h I-125 uptake, iodine organification and the iodothyronine contents in thyroglobulin, and this decrease was dose-dependent. Retinoic acid also decreased the secretion of thyroid hormones from isolated thyroid follicles into medium.