Serum levels of pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG) during normal menstrual and combined oral contraceptive cycles and relationship to immunohistological localization.

Serum levels of pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG), the major secretory protein of the endometrium during the late luteal phase of the menstrual cycle and early pregnancy, were measured serially during normal menstrual cycles and in women taking various combined oral contraceptives. Pill users were also sampled on an individual basis. Endometrium from women taking the combined oral contraceptive was examined immunohistochemically using a monoclonal antibody to alpha 2-PEG. Levels of alpha 2-PEG in the menstrual cycle sera showed consistent changes following the luteinizing hormone peak, with a greater than three-fold increase between basal levels at mid-cycle and those in the late luteal phase. Serum levels of alpha 2-PEG in the pill users remained at basal levels throughout the cycle, regardless of the progestagen in the formulation. This finding was noted in serial and individual samples from both monophasic and triphasic preparations. However, there was evidence of induction of alpha 2-PEG production at the local endometrial level when immunohistochemical staining was employed at various stages of the pill cycle. This suggests that serum levels of alpha 2-PEG may not necessarily reflect local endometrial production of the protein. These observations are discussed with reference to the proposed value of serum measurement of this protein in assessing relative progestagenic activity upon the endometrium.