The concentration of bovine placental lactogen and the incidence of different forms in fetal cotyledons and in fetal serum

The concentration of bovine placental lactogen (bPL) was determined in fetal placentomes, allantoic fluid, amniotic fluid, maternal and fetal plasma throughout pregnancy. In addition, chromatofocusing chromatography was used to separate the different forms of bPL found both in fetal serum and in placental homogenates in order to determine whether the different forms that have been reported to exist in the cotyledon are also found in the fetal circulation. Reproductive tracts were collected from cows between 109 and 247 days of pregnancy. The concentration of bPL in the fetal cotyledonary tissue was measured by both radioreceptor assay and radioimmunoassay, both assays showed that the concentration of bPL in the fetal portion of the placentomes remained constant throughout the period of pregnancy tested. The mass of the placenta increased approximately 10-fold during the period of study but the concentration of bPL in the maternal plasma was low (0.9±0.1 ng/ml) at all stages of pregnancy tested. The mean concentration of bPL (Mean ± S.E.M.) in amniotic and allantoic fluid was 0.4±0.1 and 1.2±0.2 ng/ml respectively. Fetal blood contained the highest concentrations of bPL, from 11.6 to 18.4 ng/ml, and the concentration tended to decrease with advancing gestation (slope = 0.07, P = 0.001). Several forms of bPL were found in the fetal circulation; however, a higher percentage of forms with more acidic isoelectric points were found in the fetal serum than in placental homogenates. These results suggest that either some forms of bPL are more stable or that the hormone isolated from placental tissue is not representative of the final secreted product.