Stereologic investigations on the effects of pinealectomy, melatonin and sex hormones on the rat thyroid gland.

The aim of the study was to investigate, by means of stereology, the effects of pinealectomy (PX) and melatonin on the rat thyroid gland and to explain whether sex hormone effects on the gland are related to the presence of pineal gland. Gonadectomized rats of both sexes were employed, some of them were PX and on remaining sham surgery was performed. In appropriate groups rats were treated with melatonin, testosterone and estradiol. The volume of thyroid colloid, epithelium and stroma and the epithelium/colloid ratios were estimated by stereologic methods. Neither PX nor melatonin had a significant effect on the volume of principal histologic components of the thyroid gland and did not change epithelium/colloid ratio. Obtained data suggest that exogenous melatonin partially prevented stimulatory action of testosterone on the gland while neither PX nor melatonin modified estradiol effect on the gland.