Immunochemical detection, physicochemical characterization and levels of pregnancy-associated endometrial α2-globulin (α2-PEG) in seminal plasma of men

Abstract

Pregnancy-associated endometrial α2-globulin (α2-PEG), the major secretory protein of the human uterine endometrium during the luteal phase of the menstrual cycle and early first trimester of pregnancy, has been detected by immunochemical techniques in seminal plasma. Biochemical analysis and immunoblotting has verified that immunoreactive α2-PEG in seminal plasma exhibits properties identical to those of endometrial α2-PEG, i.e. Concanavalin A-binding dimeric glycoprotein of native M(r) 56,000, subunit M(r) 28,000, average pI 4.7 and of α2-mobility. Concentration of α2-PEG in seminal plasma was 22.13 ± 2.82 μg/ml (mean ± s.e.m., n = 110) which compared to 12.02 ± 1.65 μg/ml (mean ± s.e.m., n = 48) found in amniotic fluid at 11-20 weeks of pregnancy, to 4.29 ± 1.66 μg/ml (mean ± s.e.m., n = 15) in uterine luminal fluid in women during the luteal phase and to 0.245 ± 0.025 μg/ml (mean ± s.e.m., n = 10) in sera at 10 weeks of pregnancy. This distribution is very different from that observed for pregnancy-associated placentally-derived serum proteins detected in seminal plasma. The source of α2-PEG in seminal plasma is unknown but is unlikely to be the testis because of the normal levels observed in vasectomized men. In the endometrium α2-PEG synthesis and secretion appears to be related to progesterone-dependent differentiation of the glandular epithelium. Therefore these observations suggest that a different mechanism of regulation of the gene for α2-PEG operates in the male reproductive tract.