The Protective Role of Vitamin E Against the Effects of Hyperthyroidism on the Rat Pituitary-Ovary Axis

Abstract

This study investigated the effects of an experimentally induced hyperthyroidism model on the pituitary-ovarian axis and the possible protective role of vitamin E against these adverse effects. Wistar albino rats were divided into five groups of eight animals each: control ("Cont," no any treatment); hyperthyroidism ("Hypert," L-thyroxine at 0.3 mg/kg/day); "Sham" (1 ml/day corn oil); "Hypert + vit E" (L-thyroxine (0.3 mg/kg/day and 100 mg/kg/day/1 ml vitamin E); and "Vit E" (100 mg/kg/day/1 ml vitamin E) groups. At the end of the experiment, ovarian tissues were exposed to electron microscopic and stereological analyses. Thyroid stimulating hormone (TSH), free thyroxine (FT4), follicle stimulating hormone (FSH), luteinizing hormone (LH), and superoxide dismutase (SOD) levels, as well as catalase (CAT) enzyme activity, were also determined in blood serum samples. Ovarian follicle numbers and volumes; corpus luteum and cortex volume; body weights; and TSH, FSH, and SOD levels decreased significantly in the Hypert group compared with the Cont group. However, connective tissue volume, CAT enzyme activity, and FT4 levels increased in the Hypert group compared with the Cont group. Vitamin E supplementation was observed to play a protective role on antral follicle, corpus luteum, and connective tissue volumes, CAT activity, and SOD and FSH levels. Hyperthyroidism reduces the number of ovarian follicles and may cause infertility problems. The adverse effect of hyperthyroidism on the pituitary-ovarian axis can be ameliorated by means of vitamin E, since this may have a homeostatic effect on this axis, as shown by the biochemical, histopathological, and stereological analyses in this study.