The modern lifestyle of many people takes place in conditions of "light pollution". Prolongation of the photoperiod not only inhibits the synthesis and secretion of melatonin (universal endogenous adaptogen), but also causes induction of anovulation and promotes premature puberty and premature aging, which may occur against the background of impaired secretion of sex hormones. The purpose of the study was to examine the long-term change in the light regime to the level of sex hormones, testosterone and estradiol in the blood plasma of rats. The experiment was performed on 120 Wistar rats. According to the nature of the action and intensity of lighting, we formed 3 groups (20 rats in each): K – control (intact), the animals of which were in natural light; group 12/12 – under the influence of artificial lighting for 12 hours a day: from 6 am to 6 pm and group 24/00 – under the influence of noctidial artificial lighting. Artificial lighting was carried out with an incandescent lamp with a power of 100 watts. The light intensity in the cages, which was measured using a Yu-117 luxmeter, was 40-50 lux. The content of free testosterone and estradiol was determined in the blood plasma of rats by enzyme-linked immunosorbent assay. Statistical processing of the obtained data was performed by methods of mathematical statistics. A statistically significant difference in averages was established using Student's test (t). The changes were considered significant at p≤0.05. While processing the obtained data, the ratio of testosterone/estradiol was calculated, the median estimate was given, and the oscillation ranges were 25-75% of the intervals. The study proved that in males, the change in light regime caused a statistically significant decrease in free testosterone levels and an increase in estradiol in plasma, while in females the opposite changes were observed. Hypertestosteronemia in females and hypotestosteronemia in males with changes in estradiol levels were also shown to be adaptive responses to the changes in the photoperiod. We found out that a statistically significant decrease in the ratio of testosterone/ estradiol in males (in the 12/12 group by 42.6%; in the 24/00 group – by 65%) and its increase in females (in the 12/12 group by 60.6%, in the 24/00 group – by 79%), were probably compensatory reactions to the stress factor, which was a long-term change in lighting. In general, a higher range of testosterone/estradiol index deviations in 24-hour rats (24/00) indicated that they had a more acute stress response to changes in lighting and reduced adaptability. This "adaptation fee" is generally aimed at survival, but leads to sexual dysfunction in rats

Keywords: change in the light regime, testosterone, estradiol

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