Immunological and biological activities of bovine placental lactogen in placental expiant culture

This study characterized immunological and biological activities of the bovine placental lactogen (bPL) secreted by the placental expiant obtained on Day 55, 130, 140, 146 and 270 of pregnancy. Tissues were minced and cultured for 24 hours. The bPL concentration and lactogenic activity of culture media were determined by radioimmunoassay using an anti-bPL antiserum and lymphoma cell (Nb2) bioassay, respectively. The bPL concentration in the media conditioned with cotyledons and caruncles gradually increased as gestation progressed. At term of gestation, fetal cotyledons produced a three-fold greater concentration of bPL than maternal caruncles. Lactogenic activity in conditioned media was higher in fetal cotyledons than in caruncles. Lactogenic activity in the conditioned media decreased in both the cotyledon and caruncle at term of gestation. Anti-bPL monoclonal antibody revealed a positive band of bPL in Western blot analysis, using the medium conditioned with cotyledons and caruncles collected in mid-pregnancy, however, no immunopositive band was detected in the medium conditioned with maternal caruncles at term of gestation. These results show that biological and immunochemical characteristics of bPL secreted by maternal caruncle and fetal cotyledon are different and undergo change with the advancement of gestation.