Native and recombinant bovine placental lactogens

The bovine placenta produces a wide variety of proteins that are structurally and functionally similar to the pituitary proteins from the GH/PRL gene family. Bovine placental lactogen (bPL) is a 200-amino acid long glycoprotein hormone that exhibits both lactogenic and somatogenic properties. The apparent molecular masses of purified native (n) bPL molecules (31-33 kDa) exceed 23 041 Da, which is the theoretical molecular mass of the protein core. At least six isoelectric variants (pI: 4.85-6.3) of bPL were described in cotyledonary extracts and three different bPL isoforms (pI: 4.85-5.25) were found in fetal sera. The bPL molecules that are detected in higher concentrations in peripheral circulation exhibit a more acidic pI than those present in placental homogenates. This may reflect an important glycosylation process occurring just prior to the bPL secretion. The bPL mRNA is transcribed in trophectoderm binucleate cells starting from Day 30 of pregnancy until the end of gestation. In mothers, bPL is involved in the regulation of ovarian function, mammogenesis, lactogenesis, and pregnancy stage-dependent adaptation of nutrient supplies to the fetus. Due to the higher fetal, compared to maternal concentrations of circulating hormone, it has been suggested that bPL primarily targets fetal tissues.

Radioimmunoassay of bovine placental lactogen using recombinant and native preparations: determination of fetal concentrations across gestation

Concentrations of bovine placental lactogen (bPL) were determined in fetal plasma samples by twelve double-antibody competitive radioimmunoassay systems (RIA I-XII) based on either recombinant bPL (non-glycosylated) or native bPL (glycosylated). Both preparations were used as standard and tracer, and for primary antisera production. The minimum detection limit measured by these RIA varied from 0.02 to 0.6 ng bPL mL(-1). The coefficients of correlation of different bPL RIA systems were up to 90% (P < 0.0001) when each RIA was tested against the average values of all twelve RIA systems. All developed RIA were used to investigate the incidence of different bPL isoforms in bovine fetal serum samples (n = 71). Fetal concentrations ranged from 11.8 to 35.7 ng mL(-1) at the third month and from 1.1 to 13.5 ng mL(-1) at the ninth month of gestation. They tended to decrease with advancing gestation. In general, those RIA systems that used recombinant bPL as the standard measured higher values than those using the native bPL preparation. These differences decreased toward the end of gestation (P < 0.05), suggesting a lower rate of glycosylation. Our results provide evidence of different glycosylated isoforms of bPL in fetal serum at different gestation periods.

Measurement of Ovine Pregnancy-Associated Glycoprotein (PAG) During Early Pregnancy in Lacaune Sheep

This study describes ovine pregnancy-associated glycoprotein (ovPAG) concentrations in 20 Lacaune sheep during early pregnancy. Measurements were performed by using semi-purified ovPAG as standard, tracer and immunogens for antibody production in rabbits. Antisera R780 (against ovPAG(57+59kDa)) and R805 (against ovPAG5(58+61kDa)) were used respectively in RIA-780 and RIA-805. Blood samples were collected at days 0, 18, 20, 22 and 25 after artificial insemination. From day 18 after breeding onward, the mean ovPAG concentration was significantly higher (p < 0.001) in plasma samples from pregnant ewes (n = 17) than in non-pregnant ones (n = 3). The specific activity of the tracer was 11 760 Ci/mmol in RIA-780 and 14 900 Ci/mmol in RIA-805. The minimal detection limits for RIA-780 and RIA-805 were 0.2 ng/ml and 0.3 ng/ml, respectively. The intra-assay CV of samples with low (1.0 ng/ml), medium (2.5 ng/ml) and high (4.0 ng/ml) PAG concentrations were 3%, 6% and 9% for RIA-780 and 8%, 9% and 5% for RIA-805. The inter-assay CV in the same samples were 13%, 12% and 7% for RIA-780 and 13%, 11% and 5% for RIA-805. The recovery was higher than 95% in both assays. No cross-reaction was observed with members of aspartic proteinase family as well as with other tested proteins. In both RIA-780 and RIA-805, inhibition of the binding of the tracer by antisera was parallel between standard curve and serial dilutions of pregnant ewe samples. In conclusion, the two homologous RIA systems are suitable for early quantification of ovPAG concentrations in ewe plasma samples from day 18 after breeding.