Download Effects of Darkness Stress on Thyroid Function

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 .
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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.
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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.
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Keywords— Darkness, T3, T4, Testosterone, Rat.
I. INTRODUCTION
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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
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III. RESULTS
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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
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[16] Singh DV, Turner CW. Effect of light and darkness upon thyroid secretion
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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.
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