Estrogen directly modulates circadian rhythms of PER2 expression in the uterus

Estrogen (17beta-estradiol) shortens the period of rhythmic activity in the uterus but not in the suprachiasmatic nucleus.

• Fluctuations in estrogen and progesterone levels during the estrous cycle may influence circadian rhythms in female rodents.
• Endogenously applied estrogen is associated with a shortened period of locomotor activity in rodents.
• Estrogen implants were found to affect gene expression related to the circadian clock in the suprachiasmatic nucleus and uterus.
• In tissue explant cultures from ovariectomized mice, estrogen shortened the period of PER2::LUC expression in the uterus.
• Raloxifene, an estrogen receptor modulator, reduced the effect of estrogen on the period of rhythmic expression in the uterus.
• These findings suggest that estrogen may directly influence the molecular clock in the uterus through an estrogen receptor-mediated mechanism.

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