Potency of thyroid hormone analogues in suppressing prolactin-mediated mammary growth in thyroidectomized rats.

An antagonism between prolactin and thyroxine, similar to that found in amphibian tissues at metamorphosis, has been recently shown to occur at the level of the rat mammary epithelium. This phenomenon may be implicated in the pathogenesis of human breast cancer. This experiment demonstrates that two analogues of thyroid hormone, triiodothyropropionic acid and triiodothyroacetic acid, which are relatively very weak in their calorigenic action, are as potent as thyroxine and triiodothyronine in inhibiting the prolactin-mediated mammary growth in thyroidectomized rats. The possible implication of this finding in the treatment of mammary cancer is discussed.