Yanko Roman, Levashov Mikhail, Chaka Elena, Litovka Irina, Safonov Sergey. Seasonal features of the combined effects of intermittent normobabic hypoxia and melatonin on the thyroid gland morphofunctional state. Journal of Education, Health and Sport. 2020;10(4):186-198. eISSN 2391-8306. DOI http://dx.doi.org/10.12775/JEHS.2020.10.04.021 https://apcz.umk.pl/czasopisma/index.php/JEHS/article/view/JEHS.2020.10.04.021 https://zenodo.org/record/3770209 The journal has had 5 points in Ministry of Science and Higher Education parametric evaluation. § 8. 2) and § 12. 1. 2) 22.02.2019. © The Authors 2020; This article is published with open access at Licensee Open Journal Systems of Nicolaus Copernicus University in Torun, Poland Open Access. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author (s) and source are credited. This is an open access article licensed under the terms of the Creative Commons Attribution Non commercial license Share alike. (http://creativecommons.org/licenses/by-nc-sa/4.0/) which permits unrestricted, non commercial use, distribution and reproduction in any medium, provided the work is properly cited. The authors declare that there is no conflict of interests regarding the publication of this paper. Received: 17.02.2020. Revised: 20.04.2020. Accepted: 27.04.2020. Seasonal features of the combined effects of intermittent normobabic hypoxia and melatonin on the thyroid gland morphofunctional state Roman Yanko (B,C,E,F), Mikhail Levashov (A, D), Elena Chaka (B,F), Irina Litovka (A), Sergey Safonov (G) A. A. Bogomoletz Institute of Physiology, National Academy of Sciences of Ukraine, Department of Clinical Physiology of Connective Tissue, Kiev, Ukraine Authors’ contribution / Wkład autorow: A. Study design, planning / zaplanowanie badań B. Data collection entry / zebranie danych C. Data analysis, statistics / dane analiza i statystyki D. Data interpretation / interpretacja danych E. Preparation of manuscript / przygotowanie artykułu F. Literature analysis, search / wyszukiwanie i analiza literatury G. Funds collection / zebranie funduszy Corresponding Author: Yanko Roman, A.A. Bogomoletz Institute of Physiology, Bogomoletz str., 4, Kiev, Ukraine, 01024 (e-mail: biolag@ukr.net) Roman Yanko https://orcid.org/0000-0002-0397-7517 Mikhail Levashov https://orcid.org/0000-0003-1354-2047 Elena Chaka https://orcid.org/0000-0001-7425-2751 Irina Litovka http://orcid.org/ 0000-0001-9163-3572 Sergey Safonov https://orcid.org/0000-0002-4785-0315 Abstract The aim of this work is to compare the effect of the combination influence of dosed intermittent normobaric hypoxia and melatonin in different seasons of the year on the morphofunctional state of the rats’ thyroid gland. Material and methods. The study was carried out on 48 male rats of the Wistar line. The hypoxic gas mixture (12% O2 and 88% N2) was daily given to experimental animals in intermittent mode: 15 minutes deoxygenation / 15 minutes reoxygenation for 2 hours. Melatonin was administered orally in a dose of 5 mg / kg at 10.00 a.m. The total duration of the experiment was 28 days. Histological preparations were prepared according to a standard methodic. Histomorphometry of the digital images of preparations was carried out using the computer program «Image J». Results. It was shown that the thyroid gland of rats reacted differently to the combined effects of intermittent hypoxia and melatonin at different seasons. So the signs of the gland activity were increased after influence of hypoxia and melatonin in spring. It was evidenced by a smaller area of follicles and colloid, a smaller internal diameter of the follicles and colloid-accumulation index, a greater height of the thyrocytes and follicular-colloid index, a smaller width of the interlobar, interlobular and interfollicular connective tissue interlayers compared to the control. The prolonged exposure to intermittent hypoxia and melatonin in autumn decreased the area and height of the follicular epithelium, increased the internal diameter of the follicles, decreased the follicular-colloidal index and increased the colloid-accumulation index. This indicated a decrease in the activity of the thyroid gland. Conclusions. Thus, in the spring, the morphofunctional activity of the thyroid gland is moderately increased, and in the autumn period, on the contrary, decreases. Key words: intermittent normobaric hypoxia; melatonin; thyroid gland.