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Critical period of progesterone (P) withdrawal
• P-withdrawal is the trigger for menstrual bleeding.
• Molecular mechanisms for endometrial breakdown not
elucidated.
• In non-human primate (ovariectomized macaque model): critical period of
P- withdrawal lasting 36-48h exists before menses (data from Slayden, Brenner et al).
• P replacement blocks menses 36-48h after P-withdrawal; after this P supplementation does not block menses.
Control of menstrual bleeding and endometrial repair
• Vasoconstriction of spiral arterioles
• Effective haemostasis
• Re-epithelialisation of denuded basal endometrium
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