Molecular and cellular aspects of endometrial receptivity.

Endocrine and paracrine controls regulate the endometrium during the luteal phase of the cycle to permit implantation. Part of this differentiation process is the production of a specific secretion which fills the intrauterine cavity and glandular lumen. Its molecular composition originates from the gland secretion, from transudations from stroma, from the endometrial blood vessels, and last, but not least, from cellular components of apoptotic and exfoliated cells. We have studied the secretions of all phases during the menstrual cycle using patterns evaluated by SDS-PAGE, by laser densitometry or Western blots. Uterine secretion electrophoresis (USE) permits detailed analyses of the intrauterine micromilieu and allows clinical assessment of the receptive stage of endometrium during the luteal phase. Several individual protein bands have been defined as characteristic markers for such receptive pattern. We have isolated and identified the molecular structure of several of these proteins, e.g. histones, cyclophilin, transthyretin, haptoglobin and uteroglobin. Investigations on the endocrine regulation of these proteins, were carried out on the uterine secretions of patients treated with progesterone antagonists (mifepristone and onapristone). The results demonstrate how progesterone-dependent components produce a receptive pattern, which can serve as a useful and precise marker in the clinical diagnosis of the luteal phase. Essential progesterone-dependent components differentiating during the luteal phase may provide new targets for contraceptive interventions by preventing the physiological changes typical of receptivity.