Interactions of L-Thyroxine or L-Triiodothyronine and Thyrotropin- Releasing Factor on the Release and Synthesis of Thyrotropin from the Anterior Pituitary Gland of Mice

An increase in the release and synthesis of thyrotropin (TSH) from the anterior pituitary gland followed the administration of purified porcine thyrotropin-releasing factor (TRF) to mice. The release of TSH was determined by measuring the 131I release from the thyroid gland. The synthesis of TSH was determined by measuring the change in TSH content of the anterior pituitary gland. Both Lthyroxine (T4) and L-triiodothyronine (T3) inhibitedinhibited the release of TSH produced by TRF. This is a dose-related rather than an all or none response. Complete inhibition of the TRF-TSH release response occurred with 0.3 μg T3 and partial inhibition with .03 μg. Under the same conditions, 2.7 μg T4 produced complete inhibition and 0.9 μg partial inhibition. Increasing the dose of TRF overcame the inhibition caused by T4. {Endocrinology 81: 741, 1967)