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Table of Contents
ORIGINAL ARTICLE
Year : 2020  |  Volume : 63  |  Issue : 5  |  Page : 235-243

Photo-pollution disrupts reproductive homeostasis in female rats: The duration-dependent role of selenium administrations


1 Department of Physiology, Edo University Iyamho, Edo State, Nigeria
2 Department of Physiology, University of Benin, Edo State, Nigeria
3 Department of Biomedical Sciences, Aston University Birmingham, Birmingham, England
4 Department of Microbiology, Edo University Iyamho, Edo State, Nigeria
5 Department of Anatomy, Edo University Iyamho, Edo State, Nigeria

Date of Submission08-Jul-2020
Date of Acceptance08-Oct-2020
Date of Web Publication27-Oct-2020

Correspondence Address:
Mayowa J Adeniyi
Department of Physiology, Edo University Iyamho, Edo State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/CJP.CJP_52_20

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  Abstract 

Although selenium is known to be essential for reproductive function, studies have indicated the adverse effect with its prolonged use. The present study investigated the duration-related effect of selenium administrations on reproductive hormones and estrous cycle indices in adult female Wistar rats exposed to a model of light pollution using altered photoperiod (AP). Ninety-six cyclic female Wistar rats displaying 4–5 days' estrous cycle length (ECL) and weighing 148–152 g were randomly divided into short and long experimental cohorts consisting of six groups each and spanning for 1 and 8 weeks, respectively. Each consisted of control, high selenium dose (HSE), low selenium dose (LSE), AP, AP + HSE, and AP + LSE. The rats were orally administered high dose (150 μg/kg) and low dose (100 μg/kg) of sodium selenite once per day. The estrous cycle indices were monitored. Plasma levels of follicle-stimulating hormone, luteinizing hormone (LH), estradiol (E), progesterone (P), prolactin, E/P ratio, and histology of ovary and uterine horn were evaluated. The statistical analysis was performed using Statistical Package for the Social Sciences. In AP rats, HSE and LSE caused no significant effect on LH, E, P, and E/P ratio, ECL, estrus interval (EI), and estrous cycle ratio (ECR). The effect of HSE and LSE on LH, E, P, E/P ratio, and ECL showed no duration-dependent increase, but there was a duration-dependent increase in EI and ECR at low dose. The study indicated that administration of HSE of selenium improved reproductive function in photo-pollution-exposed rats irrespective of the duration of treatment.

Keywords: Estrous cycle ratio, follicle-stimulating hormone, luteinizing hormone, photo-pollution, reproductive homeostasis, selenium


How to cite this article:
Adeniyi MJ, Agoreyo FO, Olorunnisola OL, Olaniyan OT, Seriki SA, Ozolua PO, Odetola AA. Photo-pollution disrupts reproductive homeostasis in female rats: The duration-dependent role of selenium administrations. Chin J Physiol 2020;63:235-43

How to cite this URL:
Adeniyi MJ, Agoreyo FO, Olorunnisola OL, Olaniyan OT, Seriki SA, Ozolua PO, Odetola AA. Photo-pollution disrupts reproductive homeostasis in female rats: The duration-dependent role of selenium administrations. Chin J Physiol [serial online] 2020 [cited 2020 Nov 29];63:235-43. Available from: https://www.cjphysiology.org/text.asp?2020/63/5/235/299248


  Introduction Top


Before the discovery of electric bulb by Thomas Alva Edison in 1879 and its use for public lighting, physiological functions including reproduction were governed by natural photoperiod of 12 h light/12 h dark cycle.[1] Currently, human exposure to light pollution occurs in many forms, with night work being one of the predisposing factors.[2] A study published by Science Advances in 2016[3] reveals that over one-third of the world's population live under light polluted environment. Previous studies have shown the negative outcomes of exposure to altered photoperiod (AP) on mammalian physiology including cardiovascular, nervous, endocrine, and reproductive systems. For example, on female reproductive homeostasis, indiscriminate exposure to light has been shown to impair hormonal rhythm most especially, in the hypothalamic–hypophyseal–ovarian axis, which determines the reproductive cycle and fertility.[4]

For instance, continuous illumination was shown to modulate normal nocturnal decrease in follicle-stimulating hormone (FSH) secretion in women, leading to higher prevalence of irregular ovarian cycle patterns and changes in the regular monophasic ovarian cycle and increased risk of female infertility. Nearly 96% of women exposed to light at night exhibited abnormality in follicular phase, and 64% and 58% of women showed derangements in ovulatory and luteal phases, respectively.[5] Nurses on rotating work schedule with erratic levels of light exposure were shown to exhibit greater prevalence of irregular ovarian cycle patterns, changes in the regular monophasic ovarian cycle, subfertility, longer time to pregnancy, and low birth weight.[6] It is also interesting to note that in night workers, many factors other than photo-pollution alone may be responsible for chronobiological disruption,[6] making the quest for management complex. This, therefore, highlights the need for experimental models which independently examine the role of irregular light exposure or work stress in chronobiological disruption and deranged reproductive cycle.

In chronobiology-related animal studies, pregnancy rate decreased in middle-aged mice when they were exposed to intermittent shift in light–dark cycle.[7] Female rats maintained under continuous lighting for 8 months showed long estrous cycle length (ECL), irregular cycle, prolonged estrus, and persistent vaginal cornification due to low serum level of progesterone and high estradiol/progesterone ratio.[8] Studies have shown the impacts of nutritional supplements on the maintenance of health and prevention of diseases. For example, selenium, a cofactor for glutathione peroxidase and iodothyronine deiodinase, has been shown to contribute to progesterone production of corpus luteum; maintenance of the function of the corpus luteum and placenta in the latter period of pregnancy; minimized gonadal weight loss induced by sodium arsenate and increased plasma LH, FSH, and estradiol in rats; and improved plasma progesterone exposed to doxorubicin.[9] Maternal selenium supplementation during pregnancy has been shown to improve the quality of blastocysts, ameliorate the extent of edema, reduce rough endoplasmic reticulum expansion, and increase FSH and estradiol levels in rats exposed to lead.[10]

Although in the previous study we reported that selenium supplementations prevented estrous cycle abnormality in light-deprived rats dose dependently,[11] evidence exists in support of the adverse effects of selenium following long-term exposure.[12] In view of this, we were stimulated to investigate whether the effect of selenium is duration dependent. The aim of the study was to determine the duration-dependent effect of selenium administrations on hypothalamic–hypophyseal–ovarian axis and estrus cycle indices on hypothalamic–hypophyseal–ovarian axis and estrous cycle indices in adult female Wistar rats exposed to a model of photo-pollution using AP.


  Materials and Methods Top


Animal care and management

Ninety-six cyclic female Wistar rats displaying 4–5 days' ECL and weighing between 148 and 154 g were used for the research. They were purchased from the Department of Anatomy, University of Benin, Nigeria. They were housed in polypropylene (plastic) cages (37 cm × 27 cm) with stainless steel mesh cover. The rats were given grower mash and water through feeding and drinking troughs ad libitum.

All rats were maintained in well-ventilated chambers (156 cm × 30 cm) designed in line with the method of Olayaki et al. with modification.[13],[14] The control chamber was under natural 12 h light/12 h dark cycle at an illuminance using a digital lux meter. Rats in the control chamber were regularly maintained under natural 12 h light/12 h dark cycle.

Lighting in the experimental chamber was provided by 8-W fluorescent tubes at an illuminance of 120–150 lx. The lighting schedule in the experimental chambers was based on the method of Yoshinaka et al.[15] with modification. Rats in the experimental chamber were maintained under 20 h light/4 h dark (120–150 lx).

Reagents

Sodium selenite (manufactured by Sigma Chemical Co., St. Louis, MO, USA) was obtained from Zayo-Sigma, Jos, Nigeria. Light microscope, glass slides, mercury-in-glass thermometer, glucometer (Accu-Chek, Roche Biochemical Laboratory, Mannheim, Germany), digital lux meter, weighing balance, dissecting set, needles, syringes, and chemicals were used for the study.

Animal treatments

Rats were orally administered low and high doses of sodium selenite containing 100 μg/kg and 150 μg/kg, respectively, according to the method of Kim et al.[16] with modification. Administrations were done through oral gavage once per day for 1 and 8 weeks.

Experimental procedure

The experiment was performed in accordance with the National Institutes of Health (NIH) guidelines for the care and use of laboratory animals. All rats were acclimatized under natural 12 h (light/dark cycle) (3–10 lx). As required, ethical certification/approval was obtained from the department's designated project supervisor. The rats were randomly divided into short and long experimental cohorts, each consisting of six groups of eight rats, as shown in [Table 1]. The short and long experimental cohorts spanned for 1 and 8 weeks, respectively.
Table 1: Short (1 week) and long (8 weeks) experimental cohorts

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Estrous cycle study

Estrous cycle study was done in accordance with the method described by Marcondes et al.[17] A volume of 0.1 mL of 0.9% saline solution was gently introduced 2–3 times into the vagina of the rats to produce a vaginal lavage. The pipette was withdrawn and its content was placed on a microscope slide and viewed under ×40 magnification lens of the microscope.

The estrous cycle was classified into diestrus, proestrus, estrus, and metestrus based on the cell type and density. The length of estrous and % estrous phase interval were determined. Estrous cycle ratio (ECR) was calculated according to the method of Adeniyi and Agoreyo.[18] Estrous length was calculated as the number of days required to migrate from proestrus to diestrus.

% estrus phase interval = (no. of days required for estrus phase completion)/(estrous length) × 100%

ECR = (proestrus duration + estrus duration)/(metestrus duration + diestrus duration).

Plasma preparations

The animals were euthanized after 1 and 8 weeks. In order to lessen the effect of diurnal variation in hormone level, euthanasia was carried out in the morning between 5:00 a.m. and 7:00 a.m.[6],[19] after 12 h overnight fasting. Blood sample was collected through cardiac puncture into lithium heparin bottles. The blood samples were centrifuged to obtain the plasma and the plasma was separated into a plain bottle. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, progesterone, and prolactin (PL) were assayed.

Tissue preparations

The ovaries and uterine horn were isolated, weighed and washed in normal saline. The uterine horn and ovary were preserved in separate bottles containing 10% formalin for histological studies.

Hormonal analyses using enzyme-linked immunosorbent assay

Plasma FSH, LH, estrogen, progesterone, and PL were determined using enzyme-linked immunosorbent assay.

Determination of estradiol: progesterone ratio

Estradiol:progesterone ratio was determined using the formula estradiol/progesterone.

Histological analysis

The right uterine horn and ovary were processed through graded alcohols into paraffin wax. Paraffin-embedded tissues were serially sectioned at 3 μm and stained with a modified Masson trichrome stain. The photomicrographs of the uterine horn and ovary were then obtained.

Statistical analysis

All data were expressed as mean ± standard error of the mean for six rats per group using SPSS 21 (SPSS Inc., Chicago, IL, USA). Statistically significant differences were accepted at P < 0.05. Comparisons were done using one-way analysis of variance. Least significance difference (LSD) test was used to identify the significance of pair-wise comparison of mean values among the groups.


  Results Top


Effect of altered photoperiod and selenium on estrous cycle

[Figure 1]a shows the effect of AP and selenium supplementations on ECL. Exposure to AP for 1 and 8 weeks caused a significant increase in ECL when compared with that of the control group. In AP rats, long-term treatment with high selenium dose (HSE) led to a significant decrease in ECL when compared with that in the AP group. In AP rats, administrations of either HSE or low selenium did not cause a duration-dependent effect on ECL.
Figure 1: (a) Effect of AP and selenium supplementations on estrous cycle length. *Significant difference (P < 0.05) from CTRL. aSignificant difference (P < 0.05) from AP. ySignificant difference (P < 0.05) from 1 week. (b) Effect of AP and selenium supplementations on estrous cycle ratio. *Significant difference (P < 0.05) from CTRL. ySignificant difference (P < 0.05) from 1 week. aSignificant difference (P < 0.05) from AP. CTRL: Control, HSE: High selenium dose, LSE: Low selenium dose, AP: Altered photoperiod.

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[Table 2] shows the effect of AP and selenium supplementations on estrous phase interval. After 8 weeks of exposure to AP, there was a significant increase in estrus interval when compared with that of the control group. In AP rats treated with low selenium dose, there was a duration-dependent increase in estrus interval. In AP rats, administrations of high selenium did not cause a duration-dependent effect on estrus phase interval.
Table 2: Effect of selenium supplementations and altered photoperiod on percentage estrous phase interval

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[Figure 1]b shows the effect of AP and selenium supplementations on ECR. Exposure to AP for 8 weeks caused a significant increase in ECR when compared with that of the control group. When compared with AP group, long-term treatment of AP rats with HSE caused a significant decrease in ECR. In AP rats treated with low selenium dose, there was a duration-dependent increase in ECR. In AP rats, administration of HSE did not cause a duration-dependent effect on ECR.

Effect of altered photoperiod and selenium administrations on hypophyseal hormones

[Figure 2]a shows the effect of AP and selenium supplementations on plasma FSH. Administration of HSE led to a duration-dependent increase in FSH secretion. In AP rats, administrations of either HSE or low selenium did not cause a duration-dependent effect on plasma FSH level.
Figure 2: (a) Effect of selenium supplementations and AP on plasma FSH. *Significant difference (P < 0.05) from CTRL. ySignificant difference (P < 0.05) from 1 week. aSignificant difference (P < 0.05) from AP. (b) Effect of AP and selenium supplementations on plasma LH. *Significant difference (P < 0.05) from CTRL. ySignificant difference (P < 0.05) from 1 week. aSignificant difference (P < 0.05) from AP. (c) Effect of AP and selenium supplementations on plasma prolactin. *Significant difference (P < 0.05) from CTRL. ySignificant difference (P < 0.05) from 1 week. aSignificant difference (P < 0.05) from AP. CTRL: Control, HSE: High selenium dose, LSE: Low selenium dose, AP: Altered photoperiod, LH: Luteinizing hormone.

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[Figure 2]b shows the effect of AP and selenium supplementations on plasma LH. Exposure to AP for 1 and 8 weeks resulted in a significant decrease in plasma LH when compared with that of the control group. In AP rats, administrations of either HSE or low selenium did not cause a duration-dependent effect on plasma LH level.

[Figure 2]c shows the effect of AP and selenium supplementations on plasma PL. Exposure to AP for 1 and 8 weeks resulted in a significant increase in plasma PL when compared with that of the control group. AP exposure caused a duration-dependent decrease in PL secretion. Long-term treatment with HSE and low selenium dose caused a duration-dependent decrease in PL secretion.

Effect of altered photoperiod and selenium administrations on ovarian hormones

[Figure 3]a shows the effect of exposure to AP and selenium supplementation on plasma estradiol. Exposure to AP for 8 weeks resulted in a significant reduction in plasma estradiol level when compared with that of the control group. In AP rats, administrations of either HSE or low selenium did not cause a duration-dependent effect on plasma estradiol level.
Figure 3: (a) Effect of AP and selenium supplementations on plasma estradiol. *Significant difference (P < 0.05) from CTRL. ySignificant difference (P < 0.05) from 1 week. aSignificant difference (P < 0.05) from AP. (b) Effect of AP and selenium supplementations on plasma progesterone. *Significant difference (P < 0.05) from CTRL. ySignificant difference (P < 0.05) from 1 week. aSignificant difference (P < 0.05) from AP. CTRL: Control, HSE: High selenium dose, LSE: Low selenium dose, AP: Altered photoperiod.

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[Figure 3]b shows the effect of exposure to AP and selenium supplementations on plasma progesterone. Exposure to AP for 1 and 8 weeks resulted in a significant reduction in plasma progesterone level when compared with that of the control group. In AP rats, administrations of either HSE or low selenium did not cause a duration-dependent effect on plasma progesterone level.

Effect of altered photoperiod and selenium on estradiol/progesterone ratio

[Figure 4] shows the effect of exposure to AP and selenium supplementations on estradiol/progesterone ratio. Exposure to AP for 8 weeks resulted in a significant increase in estradiol/progesterone ratio when compared with that of the control group [Figure 4]. In AP rats, administrations of either HSE or low selenium dose did not cause a duration-dependent effect on plasma estradiol/progesterone ratio [Figure 4].
Figure 4: Effect of AP and selenium supplementations on estradiol: progesterone ratio. *Significant difference (P < 0.05) from CTRL.ySignificant difference (P < 0.05) from 1 week. aSignificant difference (P < 0.05) from AP. CTRL: Control, HSE: High selenium dose, LSE: Low selenium dose, AP: Altered photoperiod.

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Effect of altered photoperiod and selenium on ovarian histology

[Figure 5] shows the effect of AP and selenium supplementations on ovarian histology. Exposure to AP for 1 week was characterized by secondary follicle and mild interstitial congestion [Figure 5]g. Long-term exposure resulted in degenerative changes within the secondary follicle [Figure 5]h. AP rats treated with HSD showed well-formed Graafian follicles after 1 and 8 weeks [Figure 5]i and [Figure 5]j. AP rats treated with low selenium dose showed corpus luteum and a secondary follicle after 1 and 8 weeks, respectively [Figure 5]k and [Figure 5]l.
Figure 5: Effect of AP and selenium on ovarian histology (H&E X400): Secondary oocyte (blue arrow), antrum (black arrow), corpus luteum (C), follicle (P), degenerating secondary follicle (D), secondary follicle (S). (a) (control – 1 week), (b) (control – 8 weeks), (c) (high selenium dose – 1 week), (d) (high selenium dose – 8 week) (e) (low selenium dose –1 week), (f) (low selenium dose –8 weeks), (g) (altered photoperiod – 1 week), (h) (altered photoperiod – 8 weeks), (i) (altered photoperiod- + high selenium – 1 week), (j) (altered photoperiod + high selenium – 8 weeks), (k) (altered photoperiod + low selenium –1 week), (l) (altered photoperiod + low selenium – 8 weeks).

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Effect of altered photoperiod and selenium on uterine histology

[Figure 6] shows the effect of AP and selenium supplementations on uterine histology. Exposure to AP for 1 week was characterized by normal uterine histology with prominent endometrial glands [Figure 6]g. Long-term exposure resulted in reduction in the number of endometrial glands [Figure 6]h. Rats in the AP group treated with HSD showed normal uterine histology with endometrial glands after 1 and 8 weeks [Figure 6]i and [Figure 6]j. Rats in the AP group treated with low selenium dose showed normal uterine histology with endometrial glands after 1 and 8 weeks [Figure 6]k and [Figure 6]l.
Figure 6: Effect of AP and selenium on uterine histology (H&E X400): Uterine gland (blue arrow), uterine cavity (black arrow). (a) (control – 1 week), (b) (control – 8 weeks), (c) (high selenium dose – 1 week), (d) (high selenium dose – 8 weeks) (e) (low selenium dose – 1 week), (f) (low selenium dose – 8 weeks), (g) (altered photoperiod – 1 week), (h) (altered photoperiod – 8 weeks), (i) (altered photoperiod + high selenium – 1 week), (j) (altered photoperiod + high selenium – 8 weeks), (k) (altered photoperiod + low selenium –1 week), (l) (altered photoperiod + low selenium – 8 weeks).

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  Discussion Top


Impaired hypothalamic–hypophyseal–ovarian axis and disruption in reproductive cycle play an important role in the etiology of female infertility. Studies have shown the impacts of exogenous factors, most especially photoperiod and nutritional factors, on reproductive function.[20],[21],[22] The present study investigated the duration-related effect of selenium administrations on hypothalamic–hypophyseal–ovarian axis and estrous cycle indices in rats exposed to a model of photo-pollution using AP.

Our study demonstrated that exposure to light pollution in the form of AP increased % estrous phase interval after 8 weeks of exposure. The significant increase in the % estrous phase interval observed in female rats that were exposed to AP for 8 weeks might be attributed to decrease in the secretion of LH. LH is involved in the orchestration of ovulation.[23],[24] Therefore, delay in ovulation occurs when LH secretion is depressed.[24] A previous study by Yoshinaka et al.[15] has enumerated the adverse impact of irregular lighting period on estrous cycle.

In rats maintained under AP, selenium administrations at high and low doses caused no significant change in estrus phase interval when compared with that of the control group rats. There was no duration-related effect of selenium administration at high dose on estrus phase interval. This implied that as the frequency of treatment increased, the preventive effect of high dose on estrus phase interval was not duration dependent in rats exposed to AP. However, administration of low selenium dose led to duration-dependent increase in % estrus phase interval in rats exposed to AP. In rats, secretion of gonadotropin begins late at diestrus followed by decline in luteal progesterone secretion with FSH overshadowing LH.[25] Therefore, prolongation of ECL noticed in female rats exposed to AP for 1 week might be attributed to poor gonadotropin output and disruption of ovarian–gonadotropin communication.[26]

We observed that selenium administrations had significant effect on ECL when compared with rats under altered photoperiod. The decrease in ECL in selenium-treated rats when compared with that of photo-pollution-exposed rats concurs with our previous findings.[11] The present study showed that there was no duration-related effect of selenium administrations at high and low doses on ECL. Apart from ECL, ECR provides information about relative durations of luteogenesis and luteolysis.[18],[22] Therefore, the significant increase in ECR in rats maintained under AP for 8 weeks could be attributed to the prolongation of estrus phase with an attendant delay in ovulation, evidenced from the present study by low LH secretion.[8],[27] We also observed that in rats exposed to AP, there was a duration-dependent increase in ECR. This implied that as the frequency of exposure to photo-pollution increased, there was an increase in ECR.

In rats maintained under AP, selenium administrations at high and low doses caused no significant change in ECR. There was also no duration-related effect of selenium administration at high dose on ECR. This implied that in AP rats, as the frequency of treatment increased, the preventive effect of high dose on ECR was sustainable. However, low selenium dose led to a duration-dependent increase in ECR in rats exposed to AP.

Furthermore, the histological investigations revealed that female rats exposed to AP were characterized by interstitial congestion after 1 week and degenerative changes in the secondary follicle after 8 weeks. These changes might be due to reduction in ovarian steroidogenic activity at estrus, evidenced by low progesterone level. We also noticed that uterine glands are prominent in selenium-treated groups. This finding agrees with the study of Sakr et al.[28] During estrus, the facilitative influence of progesterone on endometrial glands has been documented.[8],[23] The decrease in the size and density of endometrial glands noticed in rats exposed to altered photo-period might be due to the depressed progesterone secretion.

With respect to light pollution-related reproductive abnormality, there are many limitations in human studies, which make empirical data relatively unavailable. One of these limitations is difficulty in carrying out sufficient invasive analyses due to moral and ethical issues. These challenges were aptly overwhelmed by the model of this study. For instance, we showed that exposure of female rats to irregular lighting period for 8 weeks resulted in degenerative changes in the secondary follicle and reduction in the size and density of endometrial glands at estrus. Furthermore, another peculiarity of the present model when compared with other animal models of light pollution, was its tendency to reduce photo re-entrainment, a situation in which biological rhythms adapt to adjustment in external cues.

The functions of LH include formation of androgen (a substrate for estrogen) and ovulation.[8] In our study, we observed that exposure of female rats to AP reduced the secretion of LH in a duration-independent pattern. This reduction as due to increase in PL secretion as evidenced by the result of the PL analysis. PL is known to reduce the pulse frequency of gonadotropin-releasing hormone, a trigger of gonadotropin secretion.[6]

An early report by Chattopadhyay et al.[29] indicated that selenium administrations orchestrated an increase in LH secretion in sodium arsenate-exposed rats. In our study, in rats maintained under AP, selenium administrations at high and low doses caused no significant change in LH secretion. We also observed that there was no duration-related effect of selenium administrations at high and low doses. This implied that in rats exposed to photo-pollution, as the frequency of treatment increased, the protective effect of HSD and low selenium dose on LH secretion was sustainable. Conversely, there was a duration-dependent increase in LH in rats administered low selenium dose.

In females, at puberty, estradiol is produced chiefly by the ovary in little quantity by the extra-gonadal tissues including the adrenal gland, adipose tissues, and brain.[24] Our study showed that exposure of female rats to AP resulted in insignificant decrease in estradiol after 1 week of exposure. This result might be due to an increase in extra-gonadal secretion of estrogen, a characteristic feature of stress response.[30]

In rats maintained under AP, selenium administrations at high and low doses caused no significant change in estradiol secretion after 8 weeks. Reports by Chattopadhyay et al.[29] and Shen et al.[31] indicated that selenium administrations orchestrated an increase in estradiol secretion in rats exposed to sodium arsenate and lead, respectively. Although FSH plays a role in estrogen synthesis, we observed that there was no duration-related effect of selenium administrations at high and low doses in photo-pollution-exposed rats. Conversely, administration of HSE caused a duration-dependent increase in FSH. The significance of this with respect to estradiol steroidogenesis is not well understood, but the salutary role of LH profile cannot be undersized. Therefore, if the effect of HSE on LH secretion is not duration dependent, it might be difficult for the effect of HSE on the same to be duration dependent.

We observed that exposure to AP decreased progesterone secretions after 1 and 8 weeks. Prata Lima et al.[8] have previously documented light pollution-induced alteration in progesterone and estradiol: progesterone ratio. A peak secretion of progesterone occurred after 1 week.

We showed that selenium administrations at high and low doses resulted in significant increase in progesterone secretion, with a peak effect of low dose occurring after week 1 of treatment. Selenium-induced increase in progesterone secretion may be due to increase in FSH. FSH receptors are known to be present in corpora lutea in smaller quantity,[24],[32] the yellow steroidogenic structure formed at estrus.

A report by Sara and Sadeghi[33] demonstrated that selenium supplementations increased progesterone secretion in rats exposed to doxorubicin. In rats exposed to photo-pollution, we noticed that selenium administrations at high and low doses caused no significant change in progesterone secretion after 1 and 8 weeks of treatment, with peak secretion observed after 1 week in rats administered low selenium dose. In rats maintained under AP, there was also no duration-related effect of selenium administrations at high and low doses. This implied that in rats exposed to photo-pollution, as the frequency of treatment increased, the protective effect of HSE and low selenium dose on LH secretion was sustainable.

At estrus phase, estradiol/progesterone ratio has been reported to be low.[8] Low estradiol/progesterone ratio implied relative increase in progesterone secretion. In our study, we noticed that rats maintained under AP exhibited a high estradiol: progesterone ratio, with a peak level occurring after 8 weeks of exposure. This perhaps implied a relative decrease in progesterone secretion. Administrations of selenium caused a decrease in the ratio because selenium increased the secretion of luteal progesterone.[9]

Like other dietary factors,[34],[35],[36],[37],[38] we showed that in rats maintained under AP, selenium administrations at high and low doses caused no significant change in estradiol: progesterone ratio. There was also no duration-related effect of selenium administrations at high and low doses. This implied that in photo-pollution-exposed rats, as the frequency of treatment increased, the protective effect of HSE and low selenium dose on estradiol/progesterone ratio was sustainable. The duration-dependent decrease in PL observed in the present study in rats treated with HSE and low selenium dose is not worthless. Further studies will be required to clarify the physiological mechanisms underlying duration-dependent decrease in PL secretion with respect to selenium administrations.


  Conclusion Top


The study indicated that administration of HSE (150 μg/kg) improved reproductive function in photo-pollution-exposed rats irrespective of the duration of treatment.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

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