Review Article

Shift Work, Jet Lag, and Female Reproduction

Figure 1

The hypothalamus-pituitary-gonadal axis regulates reproductive cycles in female mammals. Increasing levels of estrogens released from the ovaries feedback onto the hypothalamus. When estrogen stimulation reaches a threshold, gonadotropin releasing hormone (GnRH) neurons release their product into the blood stream. GnRH acts on the pituitary to trigger a surge of luteinizing hormone (LH) which then induces ovulation. In rodents, the suprachiasmatic nucleus (SCN) of the hypothalamus provides an additional signal which regulates the timing of reproductive events. Shift work schedules, jet lag, and sleep deprivation can perturb the daily (circadian) rhythms in reproduction and “clock gene” expression. Clock gene expression has been detected in the SCN, GnRH neurons and female reproductive tissues. Estrogen can influence the pattern of expression of gene expression in some of these tissues (solid arrows). Estrogen also influences the rhythmic expression of clock-controlled outputs such as activity and body temperature (dashed arrow).
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