[Effect of cycloheximide on nuclear triiodothyronine receptors in the pituitary of the normal and hypothyroid rat].

Cycloheximide (Cy), an inhibitor of protein synthesis was found to provoke a dose-dependent decrease of the hypophysis T3 nuclear receptors (T3nR) concentration in normal rats. In thyroidectomized rats, the reduced T3nR density was found to be normalized within 3 hrs. after a single injection of T3. Pretreatment with Cy inhibited the T3 effect on its own receptors, whereas Cy given after T3 was partially or not effective. These data suggest that the half-life of T3nR in the hypophysis is short (about 3 hrs.), and that it depends on protein neosynthesis.