The importance of thyroid hormone in experimental ovarian cyst formation in gilts

The role of the thyroid gland in ovarian cyst formation in farm animals and in women has rarely been considered. Experimental data on the induction of polycystic ovarian disease (PCOS) in rats indicates the importance of thyroid function to the mechanism of this disorder. The objective of this work was to prove the role of thyroid hormones in gonadotropin-induced cystic ovarian disease (COD) in gilts. othyroid gilts (oral administration of 1 g of methylthioracyl (MTU) daily for 24 days), ovarian cysts were induced by injections of pregnant maresʹ serum gonadotropin (PMSG) (equine chorionic gonadotropin (eCG)) and human chorionic gonadotropin (hCG) (400 IU and 200 IU daily for 10 days, respectively). Gonadotropins were also injected into hyperthyroid gilts (400 μg of L-thyroxine daily for 24 days). Suitable control groups (no treatment, injected with gonadotropins, hypothyroid by application of MTU and hyperthyroid by administration of L-thyroxine) were set up. Thyroid function was monitored by estimating the total thyroxine in blood plasma using the radio-immunoassay (RIA) method. After treatment, all animals were laparatomized on Days 5–6 of the cycle and the blood samples from peripheral and utero-ovarian veins were collected by cannulation for 2–3 days following surgery. All gilts were then slaughtered and ovaries and other hormonal glands were excised, inspected and preserved for further analysis. perimental results showed that thyroid hormones in gilts demonstrate an antagonistic influence on the cyst-formative action of gonadotropins. Hypothyroid status increased ovarian sensitivity to gonadotropin action. This was visualised by marked 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 (decrease 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 the ovaries, and/or on central or peripheral interrelations between thyroid hormones and oestrogens.