Receptor Cross Talk and Interplay between Melatonin and Ovarian Thyroid Axis in a Letrozole Induced Polycystic (Pco) Rat

The objective of present study was to establish the interrelationship between thyroid and melatonin during anovulatory/letrozole induced polycystic ovarian condition on female Wister rats. Rats were procured and after acclimatization 20 rats were divided in 4 groups with 5 rats in each. They were divided as Control, Letrozole induced PCO rat (1 mg/kg BW/d), and melatonin alone (200 μg/100 g BW/d). The experiment was conducted for the duration of 28 d. Assessment of gravimetric, hormonal profile and thyroid histology and relative expression of MT1, MT2, and ERα, (thyroid, ovary) Dio2, TRα (Ovary) done followed by standard protocol. Histological observation showed shrinkages in thyroid follicles in PCO rats however exogenous melatonin maintained the cellular architecture and normal thyroid weight. PCO rats showed significantly high circulating testosterone but significant decreased in estrogen and progesterone level. Circulatory gonadotropins (LH, FSH) were noted significantly high in PCO rats. Melatonin injection to the PCO rats however reversed to the control level and restored. Circulatory TSH level in PCO rats were noted suppressed where as T3 and T4 were non-significantly increased suggesting a reciprocal relation between melatonin and thyroxine. Thyroid tissue of PCO rats expressed MT1 and MT2 in way alternate and opposite way being MT1 as up regulated whereas down regulation of MT2. Ovarian tissue of PCO rats showed reverse receptor expression to that of thyroid tissue being MT1 down regulated and MT2 was noted unregulated. Parallel relation was noted between ERα and TRα receptor expression in thyroid and ovarian tissue respectively. PCO rats resulted in up regulation of Dio2, receptor expression in a non-significant manner. Therefore, present finding suggests a fine interplay and cross talk via melatonin its two receptor MT1 , MT2 with ERα, TRα, and Dio2 thyroid and ovarian tissue as the case between ovarian thyroid axis hence maintaining a physiological trade-offs between theses gland with a tonic regulation to maintain melatonin and thyroid homeostasis during polycystic pathogenicity.