The Bioassay of Bovine Placental Lactogen*

Abstract

The Nb2 lymphoma cell bioassay was validated as a suitable tool for the measurement of lactogenic activity in bovine serum samples obtained during pregnancy. The levels of bovine PRL detected by homologous immunoassay and the levels of total lactogenic activity determined by bioassay were virtually identical in serum samples obtained from pregnant cows, suggesting that serum bovine placental lactogen (bPL) values in pregnancy are very low or absent in the cow. Random samples of milk from pregnant animals as well as amniotic and allantoic fluid samples were also found not to contain measurable levels of bPL. On the other hand, fetal serum bPL levels were detected by the Nb2 bioassay.