Effects of melatonin hormone on the thyroid follicular cells in rats: AgNOR staining and electron microscopic study

This study was undertaken to examine effects of pinealectomy and pinealectomy followed by melatonin adminis- tration on thyroid gland. For this purpose 18 male VVistar rats were used. Animals were divided into three groups. Group I and II were designated as sham-pinealectomized (control) and pinealectomized, respectively. The rats in Group III were pinealectomized and daily injected with melatonin for 1 month. At the end of the experiment, ali animals were killed by vascular perfusion. The thyroid glands of rats were removed, then some of the thyroid tissue specimens were stained with AgNOR techniçue and examined by light microscopy. AgNOR numbers in nuclei of thyroid follicular cells were counted. Some of the tissue specimens were examined by electron microscopy. İn our study, some findings proving the increase of mitoz activation along with the increase in the number of AgNOR granules in celi nuclei of thyroid epithel were observed after pinealectomy. Furthermore, lizozomes and secretory granules in the cytoplasm of thyroid follicular cells were increased. İn the melatonin injected group, the number of AgNOR granules in celi nuclei were decreased. Additionally, ultrastructural changes, which indicate the increase of celi activation and is visible in thyroid epithel cells after pinealectomy were disappeared follovving injection of melatonin. İn conclusion, it was observed that there has been an increase in thyroid epithel celi proliferation and in celi activation after pinealectomy and this increase has been reversed by melatonin injection.