Objective: To compare mRNA and protein levels of proenkephalin A (PEA) and gamma-aminobutyric acid A receptor pi subunit (piGABA-R) in human secretory endometrium before and during receptivity and to determine the cell phenotypes where they are expressed.
Design: Prospective and observational, comparing prereceptive vs. receptive stages of secretory endometrium within the same nonconceptional menstrual cycle.
Setting: University and non-governmental organization (NGO)-based academic and clinical-research facilities.
Patient(s): Seven healthy, multiparous, surgically sterilized women with spontaneous regular menstrual cycles.
Intervention(s): Endometrial biopsies were obtained on LH+3 and LH+7 within the same cycle.
Main outcome measure(s): Levels of PEA and piGABA-R mRNA were determined by real-time PCR, and protein presence, by immunofluorescence.
Result(s): The mRNA level of PEA fell, whereas that of piGABA-R increased, during endometrial receptivity. Positive immunostaining of PEA was found in the luminal and glandular epithelium, whereas that of piGABA-R was in luminal epithelium and stromal cells.
Conclusion(s): The discrete cell-phenotype localization and timing of the changes in the level of PEA and of piGABA-R mRNA and protein suggest an important role for these molecules in switching the human endometrium from a refractory to a receptive state.