Development and validation of a radioimmunoassay for human secretory 'pregnancy-associated endometrial alpha 2-globulin' (alpha 2-PEG) and detection in serum during pregnancy.

Abstract

A specific and sensitive radioimmunoassay has been developed for pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG), the major secretory protein of the human endometrium during the mid- to late-luteal phase of the menstrual cycle and first trimester of pregnancy. This assay enabled alpha 2-PEG to be measured in the cytosolic extracts of endometrium, amniotic fluid, seminal plasma and in pregnancy sera. The concentration of alpha 2-PEG in cytosols prepared from mid-secretory endometrium was 44-fold higher than in those from proliferative endometrium and a further 30-fold increase during the first trimester in comparison with mid-secretory endometrium. Levels of alpha 2-PEG in amniotic fluid (15-20 weeks) and seminal plasma were 15 +/- 4 and 55 +/- 7 micrograms/ml, respectively. With the exception of sera, where alpha 2-PEG was undetectable using rocket immunoelectrophoresis, estimates of alpha 2-PEG levels in these compartments, measured by rocket immunoelectrophoretic and RIA assays were comparable, although for seminal plasma 2.5-fold higher estimates were obtained by RIA. Detectable levels of alpha 2-PEG were obtained in 253 of 275 (92%) pregnancy sera tested. During pregnancy, peak levels were detected between weeks 6 and 11 but these represented only 2% of the levels detected in amniotic fluid. These observations support evidence from in vitro studies that alpha 2-PEG is a product of the secretory glandular epithelium, a tissue prominent in the first trimester and whose principal secretory route during pregnancy is into the amniotic fluid.(ABSTRACT TRUNCATED AT 250 WORDS)