Article Melatonin preserves ovarian tissues of rats exposed to chronic TCDD: An electron microscopic approach to effects of TCDD on ovarian cells Semir Gu¨ l, Mehmet Gu¨ l and Birgu¨ l Yigitcan Abstract 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a toxic agent and has disruptive effects on reproductive tis- sues in females. TCDD disrupts the hormonal regulation of the body and decreases the production of mel- atonin. In this study, we investigated the protective effects of melatonin supplements against the toxic effects of TCDD on ovaries of female rats. TCDD caused a significant decrease in the average number of corpora lutea and follicles per tissue section (2.1 + 0.7; 2.3 + 0.8, respectively), whereas these numbers were maintained in the melatonin supplemented group (5.0 + 0.8; 5.1 + 0.8, respectively) and were similar to the control group (5.3 + 1.0; 5.9 + 0.9, respectively). Electron microscopic analysis showed that the disruption of ultrastructure components such as cell membrane and organelles due to TCDD exposure was inhibited by melatonin sup- plements. This study suggested that melatonin has a protective and a possible ameliorative effect over his- topathological damage of rat ovaries exposed to TCDD. Keywords 2,3,7,8-Tetrachlorodibenzo-p-dioxin, ovary, melatonin, rat, dioxins Received 23 August 2017; Revised 25 September 2017; Accepted 11 December 2017 Introduction 2,3,7,8-Tetrachlorodibenzo- p-dioxin (TCDD), the most toxic member of the halogenated aromatic hydrocarbons, is a prevalent and persistent environ- mental contaminant formed as a synthesis side product of herbicides production and overuse of herbicides, waste incineration and combustion processes, paper bleaching, and the manufacture of plastics (Jun et al., 2011; Poland and Knutson, 1982; Yoshizawa et al., 2007). This toxic agent is able to pass from environment to humans through the food chain by absorption by the gastrointestinal system (Hutz, 1999). TCDD has a variety of adverse biologi- cal effects, including carcinogenesis, immune and hematopoietic dysfunction, neuronal cell damage (Aylward et al., 2005; Baldridge et al., 2015; Cole et al., 2003), developmental defects, impairment ovu- lation, and fertility reduction (Kakeyama and Tohyama, 2003). TCDD is classified as an endo- crine-disturbing compound by altering endocrine hormone synthesis (Kakeyama and Tohyama, 2003; Linden et al., 1991). Experimental data indicated that melatonin is one of these endocrine hormones targeted by TCDD, and its production decreased dramatically and consider- ably in rats upon TCDD exposure (Pohjanvirta et al., 1996). Melatonin, chemically N-acetyl- 5-methoxy tryptamine, is primarily produced by the pineal gland in humans and acts as an endocrine hor- mone by passing into the blood circulation (Hardeland et al., 2006). It exhibits numerous physiological and metabolic functions such as an antioxidant, circadian Department of Histology and Embryology, Faculty of Medicine, _ Ino¨nu¨ University, Malatya, Turkey Corresponding author: Semir Gu¨l, Department of Histology and Embryology, Faculty of Medicine, _ Ino¨nu¨ University, Malatya 44280, Turkey. Email: semir.gul@inonu.edu.tr Toxicology and Industrial Health 1–9 © The Author(s) 2018 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0748233717754174 journals.sagepub.com/home/tih