THE IMPORTANCE OF THYROID-HORMONE IN EXPERIMENTAL OVARIAN-CYST FORMATION IN GILTS

The role of the thyroid gland in ovarian cyst formation in farm animal s and in women has rarely been considered. Experimental data on the in duction of polycystic ovarian disease (PCOS) in rats indicates the imp ortance of thyroid function to the mechanism of this disorder. The obj ective of this work was to prove the role of thyroid hormones in gonad otropin-induced cystic ovarian disease (GOD) in gilts. In hypothyroid gilts (oral administration of 1 g of methylthioracyl (MTU) daily for 2 4 days), ovarian cysts were induced by injections of pregnant mares' s erum gonadotropin (PMSG) (equine chorionic gonadotropin (eCG)) and hum an chorionic gonadotropin (hCG) (400 IU and 200 IU daily for 10 days, respectively), Gonadotropins were also injected into hyperthyroid gilt s (400 mu g of L-thyroxine daily for 24 days), Suitable control groups (no treatment, injected with gonadotropins, hypothyroid by applicatio n of MTU and hyperthyroid by administration of L-thyroxine) were set u p. Thyroid function was monitored by estimating the total thyroxine in blood plasma using the radioimmunoassay (RIA) method, After treatment , all animals were laparatomized on Days 5-6 of the cycle and the bloo d samples from peripheral and utero-ovarian veins were collected by ca nnulation for 2-3 days following surgery, All gilts were then slaughte red and ovaries and other hormonal glands were excised, inspected and preserved for further analysis. The experimental results showed that t hyroid hormones in gilts demonstrate an antagonistic influence on the cyst-formative action of gonadotropins. Hypothyroid status increased o varian sensitivity to gonadotropin action. This was visualised by mark ed hypertrophy of the ovaries and multiple follicular cysts were also found in both ovaries. In contrast, the hyperthyroid animals showed a reduced sensitivity to the cyst-formative action of gonadotropins (dec rease of ovarian dimensions, small numbers of cysts). The mechanism of antagonistic thyroid-gonadotropin relations may be based on negative interactions between thyroid hormones and gonadotropin receptors in th e ovaries, and/or on central or peripheral interrelations between thyr oid hormones and oestrogens.