REGULATION OF THYROTROPIN-ALPHA AND THYROTROPIN-BETA SUBUNIT MESSENGER-RNA LEVELS BY ANDROGENS IN THE FEMALE RAT

Thyroid and steroid hormones act by similar mechanisms to influence gene expression in the anterior pituitary gland. The genes encoding the common α and TSH-β glycoprotein subunits are known to be regulated by thyroid hormones; we report here the effects of androgen administration on levels of α and TSH-β mRNA in pituitary cytoplasm in the euthyroid and hypothyroid female rat. Dihydrotestosterone (DHT) suppressed both α and TSH-β mRNAs to levels lower than those found in untreated animals; a similar reduction was seen in hypothyroid animals treated with DHT. A biphasic response of TSH-β mRNA was seen following administration of tri-iodothyronine (T3) to hypothyroid rats, with early stimulation followed by later inhibition; these changes were also evident after administration of T3 to androgen-treated animals, although mRNA levels were again suppressed. The effects of testosterone were similar to those of DHT. In contrast to the changes in mRNA levels, androgen administration did not lead to significant alterations in serum TSH concentrations or pituitary TSH content. These results indicate that, like thyroid hormones, androgens suppress both α and TSH-β subunit mRNA levels in the female rat. Androgens, however, exert differential effects on TSH synthesis and release which contrast with those of thyroid hormones.