Serum levels of pregnancy-associated endometrial {alpha}-globulin ( {alpha}-PEG) during normal menstrual and combined oral contraceptive cycles and relationship to immunohistologiacl localization

Serum levels of pregnancy-associated endometrial 2-globulin(2-PEG), the major secretory protein of the endometrium duringthe late luteal phase of the menstrual cycle and early pregnancy,were measured serially during normal menstrual cycles and inwomen taking various combined oral contraceptives. Pill userswere also sampled on an individual basis. Endometrium from womentaking the combined oral contraceptive was examined immunohistochemicallyusing a monoclonal antibody to 2-PEG. Levels of 2-PEG in themenstrual cycle sera showed consistent changes following theluteinizing hormone peak, with a greater than three-fold increasebetween basal levels at midcycle and those in the late lutealphase. Serum levels of 2-PEG in the pill users remained at basallevels throughout the cycle, regardless of the progestagen inthe formulation. This finding was noted in serial and individualsamples from both monophasic and triphasic preparations. However,there was evidence of induction of 2-PEG production at the localendometrial level when immunohistochemical staining was employedat various stages of the pill cycle. This suggests that serumlevels of 2-PEG may not necessarily reflect local endometrialproduction of the protein. These observations are discussedwith reference to the proposed value of serum measurement ofthis protein in assessing relative progestagenic activity uponthe endometrium