Biological rhythms and fertility: the hypothalamus–pituitary–ovary axis

Elena Toffol,1 Oskari Heikinheimo,2,3 Timo Partonen1 1Department of Health, National Institute for Health and Welfare (THL), 2Department of Obstetrics and Gynecology, University of Helsinki, Helsinki, 3Kätilöopisto Hospital, Helsinki University Hospital, Helsinki, Finland Abstract: In addition to normal physiological processes, a number of pathological conditions exhibit diurnal and seasonal fluctuations in their incidence. These biological rhythms are generated by the circadian clocks that adjust their functions and adapt to the habitat. Misalignment of biological rhythms and disrupted functions of the circadian clocks may eventually have a negative impact on reproduction, which is the focus of this review. A large body of literature from animal studies has demonstrated the role of core clock genes and clock-controlled genes in regulation of reproductive events. In contrast, only a few studies, mostly epidemiological ones, suggest that perturbations of the circadian clock functions, eg, due to shift work or jet lag, compromise human reproduction. Keywords: animal, circadian, diurnal, human, reproduction