Razi Journal of Medical Sciences

Background: Studies have shown that variation in light-dark cycle influences secretion of many hormones. The aim of this study was to investigate the effects of different periods of darkness on serum level of LH, FSH, testosterone and cortisol in male rats.

Methods: In this laboratory experimental study, 30 male Wistar rats were randomly divided into control (exposed to 12h light - 12h dark), and experimental (exposed to13, 15, 18 or 21h darkness/day) groups,and there were 6 rats in each group. After 8 weeks, blood samples were collected and following serum collection, the levels of LH, FSH, testosterone and cortisol were measured. The data were analyzed using ANOVA.

Results: Serum LH, FSH levels significantly decreased in rats exposed to darkness for 18 and 21 h/day compared with control animals (p<0.05). Serum level of testosterone and cortisol was significantly decreased in all groups exposed to darkness compared to control animals. Serum level of DHEA significantly decreased in groups exposed to darkness for 15, 18 and 21 h/day compared with control animals.

Conclusion: The findings of this study suggest that prolonged periods of darkness results in decreased serum level of testosterone, cortisol and DHEA and leads to increased LH and FSH according to which, darkness can be considered as a factor leading to sexual disorders  and disorders related to cortisol.