Abstract
BackgroundThe involvement of placental lactogen (PL) in the regulation of foetal growth has been investigated in different species by in vivo immunomodulation techniques. However, when circulating antibodies are present together with the hormone, the procedure for hormonal measurement becomes considerably complex. The aim of this study was the immunoneutralization of bovine placental lactogen (bPL) concentrations in bovine foetal circulation by direct infusion of rabbit anti-bPL purified immunoglobulins (IgG) via a foetal catheter (in vivo study). The ability of a RIA based on guinea pig anti-bPL antiserum, for the measurement of bPL concentrations in samples containing exogenous rabbit anti-bPL immunoglobulins, was also analyzed in in vitro and in vivo conditions.MethodsSix bovine foetuses were chronic cannulated on the aorta via the medial tarsal artery. Infusion of rabbit anti-bPL IgG was performed during late gestation. Pooled rabbit anti-bPL antisera had a maximal neutralization capacity of 25 μg bPL/mL of immunoglobulin. Interference of rabbit anti-bPL immunoglobulin with radioimmunoassay measurement using guinea pig anti-bPL as primary antibody was first evaluated in vitro. Polyclonal anti-bPL antibodies raised in rabbit were added in foetal sera to produce 100 samples with known antibodies titers (dilutions ranging from 1:2,500 till 1:1,280,000).Result(s)Assessment of the interference of rabbit anti-bPL antibody showed that bPL concentrations were significantly lower (P < 0.05) in samples added with dilutions of rabbit antiserum lower than 1:80,000 (one foetus) or 1:10,000 (four foetuses). It was also shown that the recovery of added bPL (12 ng/mL) was markedly reduced in those samples in which exogenous rabbit anti-bPL were added at dilutions lower than 1:20,000. Concentrations of foetal bPL were determined in samples from cannulated foetuses. In foetuses 1 and 6, bPL concentrations remained almost unchanged (<5 ng/mL) during the whole experimental period. In Foetus 3, bPL concentrations decreased immediately after IgG infusion and thereafter, they increased until parturition.Conclusion(s)The use of a bPL RIA using a guinea pig anti-bPL as primary antiserum allowed for the measurement of bPL concentrations in foetal plasma in presence of rabbit anti-bPL IgG into the foetal circulation. Long-term foetal catheterization allowed for the study of the influence of direct infusion of anti-bPL IgG on peripheral bPL concentrations in bovine foetuses.
Highlights
Growth hormone (GH), prolactin (PRL), and placental lactogen (PL) are members of a family of polypeptide hormones that are thought to have arisen from a specific receptor for GH, whereas the PRL receptor (PRLR) was considered specific for PRL and PL
Characteristics of RIA used for bovine placental lactogen (bPL) measurement in foetal samples By using guinea pig anti-bPL antiserum, displacement of the standard inhibition curve ranged from 98 to 13% of binding (B/B0)
The binding activity measured as B/T (%) ranged from 3 to 27% in samples containing anti-bPL dilutions ranging from 1:1,280,000 to 1:2,500, respectively
Summary
Growth hormone (GH), prolactin (PRL), and placental lactogen (PL) are members of a family of polypeptide hormones that are thought to have arisen from a specific receptor for GH, whereas the PRL receptor (PRLR) was considered specific for PRL and PL. Different methods have been proposed to detect and to eliminate this interference in radioimmunoassay (RIA) systems [10] These include serial dilutions of the sample [11], polyethylene glycol precipitation [12], blocking with nonimmune serum [13] and use of alternative antibodies reacting with epitopes and believed to be distinct from those recognized by circulating antibodies [14]. The involvement of placental lactogen (PL) in the regulation of foetal growth has been investigated in different species by in vivo immunomodulation techniques. The aim of this study was the immunoneutralization of bovine placental lactogen (bPL) concentrations in bovine foetal circulation by direct infusion of rabbit anti-bPL purified immunoglobulins (IgG) via a foetal catheter (in vivo study). The ability of a RIA based on guinea pig anti-bPL antiserum, for the measurement of bPL concentrations in samples containing exogenous rabbit anti-bPL immunoglobulins, was analyzed in in vitro and in vivo conditions
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