Placental protein 12 (PP12) in menstrual fluid

In a previous study we found placental protein 12 (PP12) in the human endometrium. We now show that PP12-like immunoreactive material is released into menstrual fluid where it occurs at concentrations from 43 to 32 000 micrograms/1. The PP12 levels in menstrual fluid are 2- to 2000-fold higher than in serum of the same individuals thus suggesting that the protein either concentrates or is produced in the endometrium. The addition of protease inhibitors has no effect on the PP12 levels. In radioimmunoassay, the dose-response curves of menstrual fluid PP12 and placental PP12 are parallel. Experiments with fused rocket immuno-electrophoresis show that menstrual and placental PP12 are indistinguishable from each other. In gel filtration, menstrual PP12 has the same molecular weight as that of purified placental PP12. By immuno-peroxidase staining, PP12 is localized in the glandular epithelial cells of the menstrual endometrium. The glandular localization and high concentration of PP12 in menstrual fluid, as compared with PP12 levels in serum and endometrium, suggest that PP12 may be secreted by the endometrium.