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International Conference on Chemical, Agricultural and Medical Sciences (CAMS-2014) May 2-3, 2014 Antalya (Turkey) Effects of Darkness Stress on Thyroid Function Ghadiri E*, Ahmadi R, and Nargesi II. MATERIAL AND METHODS Abstract—Studies have shown that alteration in photoperiod influences secretion of many hormones. The aim of this study was to investigate the effects of long periods of darkness as a type of stress on serum levels of T3 and T4 in male rats. In this laboratory experimental study, male Wistar rats were randomly divided to control group, and groups exposed to1or 9 h/day of 6 rats in each group. The subjects were artificially exposed to darkness. After 8 weeks, blood samples were collected using cardiac puncture method and following serum collection, the levels of T3 and T4 were measured by radioimmunoassay. The data were statically analyzed using ANOVA. The results of the present study show that there was not significant differences in serum levels of T3 and T4 in rats exposed to darkness for 1 h/day compared with control animals. However, serum levels of T3 and T4 were significantly decreased in rats exposed to darkness for 9 h/day compared with control group (P<0.05). The findings suggest that prolonged periods of darkness can reduce thyroid activity and serum levels of thyroid hormone, according to which, it is suggested that darkness can be considered as a probable factor in hypothyroidism occurrence . 1B A. Animals Adult Wistar rats weighting 200±30g were purchased and raised in our colony from an original stock of Pasteur institute (Tehran, Iran).The temperature was at 23±2 0C and animals kept under a schedule of 12h light:12h darkness (light on at: 08: 00 a.m.) with free access to water and standard laboratory chow. Care was taken to examine the animals for general pathological symptoms. Food was withheld for 12-14h before death. 5B B. Protocol of Study In this laboratory experimental study, male Wistar rats were randomly divided to control group, and groups exposed to1or 9 h/day of 6 rats in each group. The subjects were artificially exposed to darkness. After 8 weeks, blood samples were collected using cardiac puncture method and following serum collection, the levels of T3 and T4 were measured by radioimmunoassay. All animal experiments were carried out in accordance with the guidelines of Institutational Animals Ethics Committee. 6B Keywords— Darkness, T3, T4, Testosterone, Rat. I. INTRODUCTION 0B T HE thyroid hormones, triiodothyronine (T3) and thyroxine (T4) are tyrosine-based hormones produced by the thyroid gland that are primarily responsible for regulation of metabolism[1], [2].Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body [3]. Stress of different kinds including darkness stress influence many functions of body such as endocrine system [4]-[8] and immune system [9]. In fact, many hormonal changes can be occurred during stress [10]. Studies show that changes in photoperiodic cycles have effects on hormonal secretion of rats exposed to stress [11] and also thyroid gland function [12]-[18]. The aim of this study was to investigate the effects of long periods of darkness as a type of stress on serum levels of T3 and T4 in male rats. C. Statistical Analysis All values are presented as mean ± S.E.M. Statistical significance was evaluated by one-way analysis of variance (ANOVA) using SPSS 19. Significance was measured using Fisher’s least significant for the exact P values and significant differences are noted in the results. Differences with P<0.05 were considered significant 7B III. RESULTS 2B Table I shows serum levels of T3 and T4 in male rats. TABLE I SERUM CONCENTRATIONS OF T3 AND T4 IN CONTROL AND RATS EXPOSED TO DARKNESS FOR 1 OR 9H/DAY. The data are indicated as mean ± SEM . P values are expressed in comparison with control group. N.S. represents non significant difference. The results of the present study show that there was not significant differences in serum levels of T3 and T4 in rats exposed to darkness for 1 h/day compared with control animals. However, serum levels of T3 and T4 were Elnaz Ghadiri (*corresponding author) is with Department of Biology, Faculty of Basic Sciences, Islamic Azad University, Eslamshahr Branch, Eslamshahr, Iran (e-mail: [email protected]). Rahim Ahmadi (PhD) is with the Department of Physiology, Faculty of Basic Sciences, Islamic Azad University, Hamedan Branch, Hamedan, Iran. (e-mail: [email protected]). Sanaz Nargesi (MSc) is with Department of Parasitology, Faculty of Medicine, Tehran University, Tehran, Iran (e-mail: [email protected]) http://dx.doi.org/10.15242/IICBE.C514077 39 International Conference on Chemical, Agricultural and Medical Sciences (CAMS-2014) May 2-3, 2014 Antalya (Turkey) [13] Toutain J. Effect of darkness and cold on the thyroid gland of the green frog (Rana esculenta Linne). Ann Endocrinol (Paris). 1961 Nov-Dec;22:886-97. [14] Pontriano G, Meites J. The effect of continuous light and darkness on thyroid function in mice. Eendocrinology. 1951 Feb;48(2):217-224. significantly decreased in rats exposed to darkness for 9 h/day compared with control group (P<0.05). IV. DISCUSSION http://dx.doi.org/10.1210/endo-48-2-217 [15] David S. Effects of the Environment, chemicals and drugs on thyroid function. 2010. Available at: http://www.thyroidmanager. org/chapter/effects-of-the-environment-chemicals-and-drugs-on-thyroid-fun ction.html. Accessed 25 Dec, 2012. [16] Singh DV, Turner CW. Effect of light and darkness upon thyroid secretion rate and on the endocrine glands of female rats. Proc Soc Exp Biol Med. 1969 Sep;131(4):1296-9. Our study indicated that serum T3 and T4 levels did not significantly change in rats exposed to darkness for 1h/day compared with control rats but significantly decreased in groups exposed for 9h/day compared to control animals. Studies show the effects of light and darkness on TSH level [17], [18]. Although there are reports showing that some stressors do not influence TSH level [19], several findings show that stress can suppress pituitary gland, in turn may inhibit TSH secretion [20]. In accordance with our finding, the studies indicate the effect of photoperiodism on pineal-thyroid-gonadal axis [21]. In effect, the stimulation of thyroid gland is mediated via neuroendocrine reflexes from the hypothalamus, which increases thyrotropin-releasing hormone secretion and consequent thyroid hormone release [22], [23]. So, it is conceivable that prolonged darkness can affect on hypothalamus, by which influence thyroid gland secretion. http://dx.doi.org/10.3181/00379727-131-34091 [17] Laakso ML, Porkka-Heiskanen T, Stenberg D, Johansson G, Männistö PT. Lighting conditions affect serum and pituitary TSH in male rats. Am J Physiol. 1990 Aug;259(2 Pt 1):E162-9. [18] Martino E, Bambini G, Vaudagna G, Breccia M, Baschieri L. Effects of continuous light and dark exposure on hypothalamic thyrotropin-releasing hormone in rats. J Endocrinol Invest. 1985 Feb;8(1):31-3. http://dx.doi.org/10.1007/BF03350633 [19] Martí O, Gavaldà A, Jolín T, Armario A. Acute stress attenuates but does not abolish circadian rhythmicity of serum thyrotrophin and growth hormone in the rat. Eur J Endocrinol. 1996 Dec;135(6):703-8. http://dx.doi.org/10.1530/eje.0.1350703 [20] Rinehart A. Stress and Thyroid Function. 2012.Avaiable at: http://www. Stress and Thyroid Function Dr_ Alex Rinehart.mht. Accessed: Dec 25,2012. [21] Shavali SS, Haldar C. Effects of continuous light, continuous darkness and pinealectomy on pineal-thyroid-gonadal axis of the female Indian palm squirrel, Funambulus pennanti. J Neural Transm. 1998;105(4-5):407-13. V. CONCLUSION 4B The findings suggest that prolonged periods of darkness can reduce thyroid activity and serum levels of thyroid hormone, according to which, it is suggested that darkness can be considered as a probable factor in hypothyroidism occurrence. http://dx.doi.org/10.1007/s007020050066 [22] Zoeller TR. Environmental chemicals targeting thyroid. Hormones (Athens). 2010 Jan-Mar;9(1):28-40. http://dx.doi.org/10.14310/horm.2002.1250 [23] Paakkonen T. Melatonin and thyroid hormons in the cold and darkness. 2010 Acta Univ. Oul. D 1045:1-45. ACKNOWLEDGMENT This research has been done with the support of Islamic Azad University-Hamedan Branch. We appreciate all who helped us to exert the present study. Elnaz Ghadiri (Corresponding author) is with Department of Biology, Faculty of Basic Sciences, Islamic Azad University, Eslamshahr Branch, Eslamshahr, Iran. REFERENCES [1] Thyroid function. 2012. Avaiable at:http://www. mcb.berkeley.edu/courses/mcb135e/thyroid.html. [2] What is T3. 2012. Available at: http://www. What is T3 - T3 (Liothyronine Sodium).html. Accessed 10 Dec 2012. [3] Thyroid-Stimulating Hormone (TSH). 2010. Avaiable at: http:// www.webmd.com/a-to-z-guides/thyroid-stimulating-hormone-tsh. Accessed 18 Dec 2012. [4] Centre for Stress Management: Definitions of stress. 1999. Anaiable at: http://www.managingstress.com/articles/definition.htm. Accessed:29 Dec 2012. [5] The Nature of Stress. 1981. Avaiable at: http://www .icnr.com/articles/the-nature-of-stress.html. Accessed: 20 Dec 2012. [6] Mental stress. 2002. Avaiable at: http://www. medical-dictionary.thefreedictionary.com/mental+stress. Accessed: 25 Dec 2012. [7] WHAT IS STRESS.2010. AVAILABLE AT: WHAT IS STRESS & CAUSE OF STRESS.HTM. ACCESSED 27 DEC 2012. [8] Environmental stress. Available at: environment cause of stress.pdf. Accessed 27 Dec 2012. [9] C. Segerstrom S, E.Miller G. Psychological Stress and the Human Immune System: A Meta-Analytic Study of 30 Years of Inquiry. Psychol Bull. 2004 July; 130(4): 601–630. [10] Ranabir S, Reetu K. Stress and hormones. Indian J Endocrinol Metab. 2011 Jan-Mar; 15(1): 18–22. [11] Paluch A, Buntner B, Ostrowska Z, Kniazewski B. Light and darkness effect on adrenocortical secretion of rats exposed to stress. Acta Physiol Pol. 1983 Jul-Aug;34(4):431-5. [12] Mayerson HS. The effect of light and of darkness on the thyroid gland of the thyroig gland of the rat. AJP. 1935 Oct;113(3):659-662. http://dx.doi.org/10.15242/IICBE.C514077 40