Pregnancy-associated endometrial [alpha]2-globulin/beta-lactoglobulin homologue - Scientific and clinical studies.

Pregnancy-associated endometrial [alpha]2-globulin ([alpha]2-PEG) is the major endometrial secretory protein of the late luteal phase of the menstrual cycle. It is expressed in the glandular epithelium between days 19-21 of the cycle. Serum levels reflect local production, a rise which continues until menstruation being noted from day LH+6. Its expression is triggered by serum progesterone so that a rise in [alpha]2-PEG has been linked with ovulation. The continuing rise in [alpha]2-PEG production is independent of the sex steroids and its regulation in the second half of the luteal phase differs from the first half. A similar triggering response can be elicited with exogenous progestogens in the postmenopausal state. Local expression in the glands of women taking the combined oral contraceptive is not reflected in the serum levels. An absent rise in serum levels has been identified in ovulatory infertile women. Serum levels in assisted conception do not vary if implantation occurs, although the rise in serum levels seen throughout the first trimester may be absent in association with a spontaneous abortion. Endometriotic tissue expresses [alpha]2-PEG but no other sites of expression of the protein outside the reproductive tract have been identified. Immunopositivity has been seen in the epithelium of fallopian tubes and although [alpha]2-PEG is not suitable as a marker of endometrial carcinoma it has been identified in ovarian carcinoma. The regulation of [alpha]2-PEG in vitro using tissue culture techniques differs from that in vivo and occurs regardless of the stage of the cycle that the endometrium is retrieved and of the presence of progesterone. [alpha]2-PEG is a marker of the glandular epithelium of the endometrium in the late luteal phase which can be measured in the serum and results from progesterone action on the endometrium.