Competition Between Thyroxine and TRF at the Pituitary Level in the Release of TSH. ∗

Summary

When increasing amounts of thyroxine are administered to rats otherwise given an invariable dose of TRF, a dose of thyroxine is found to completely inhibit the TSH-releasing activity of that dose of TRF. Conversely, when increasing amounts of TRF are administered to animals pretreated with an invariable quantity of thyroxine known to inhibit the TSH releasing activity of several doses of TRF, a dose of TRF is eventually reached that will overcome the inhibitory effect of that amount of thyroxine. Neutron activation of a highly purified preparation of hypothalamic TRF failed to reveal presence of iodine in the TRF molecule.