The role of circadian rhythms in the functioning of male reproductive system.

Introduction. Circadian rhythms determine the functioning of all organ systems, including endocrine organs, and the synthesis of many hormones follow the biological clock. Melatonin is a hormone of the epiphysis and it plays a key role in the creating of circadian rhythms, and testosterone, the main sex hormone in men, is involved in many metabolic processes in the male body, including the functioning of the reproductive system. The link between infertility and circadian rhythm disturbances caused by external factors has been increasingly reported. The aim. Investigate the influence of melatonin and circadian rhythms on fertility and testosterone levels in men, and to analyze the mechanisms of infertility development when melatonin metabolic pathways are disturbed. Materials and methods. Literature search was conducted in PubMed, Scopus and еLibrary databases with inclusion of papers published in the last 5 years. Results. The review reveals the characteristics of epiphysis and male reproductive system functioning, describes the connection between circadian rhythms and reproductive system, the role of melatonin in its functioning, the features of testosterone metabolism and the influence of genetic and environmental factors on the epiphysis-gonadal axis functioning. The mechanisms of pleiotropic regulation of testosterone levels by melatonin, genetic factors that also significantly alter the functioning of epiphysis-gonadal axis and the prevalence of reproductive disorders in cohorts exposed to circadian rhythm disturbances are presented. Conclusion. Circadian rhythms and the reproductive system have multiple interrelationships that provide diurnal and seasonal changes in the synthesis of sex hormones, including testosterone, affecting spermatogenesis, fertility, metabolism and behavioral patterns. Sleep-wake cycle disorders and changes in biological rhythms, which are characteristic of life in modern society, should be considered as risk factors for infertility and erectile dysfunction and taken into account in patients’ management.