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Journal of Dairy Science Vol. 83 No. 3 452-458
© 2000 by American Dairy Science Association ®
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A Homologous Radioimmunoassay for Quantification of Insulin-Like Growth Factor-Binding Protein-2 in Blood from Cattle

L. Vleurick 1, R. Renaville 1, M. VandeHaar 2, J. L. Hornick 3, L. Istasse 3, I. Parmentier 1, C. Bertozzi 1, C. Van Eenaeme 3, and D. Portetelle 1

1 Department of Animal Physiology and Molecular Biology, Gembloux Agricultural University, Belgium
2 Department of Animal Science, Michigan State University, East Lansing 48824
3 Department of Nutrition, Faculty of Veterinarian Medicine, University of Liège, Belgium

Insulin-like growth factor-I and -II (IGF-I, IGF-II) circulate in biological fluids bound to six different IGF-binding proteins that regulate IGF bioactivity. The IGF-binding protein-2 is regulated by growth hormones, and its concentration depends on nutrition and physiological state. Specific antibodies directed against bovine IGF-binding protein-2 were produced, and IGF-binding protein-2 levels in bovine blood samples were quantified by radioimmunoassay. Parallel displacement curves showed strong cross-reactivity with bovine and ovine plasma, were low with porcine plasma, and no cross-reactivity with rat or chicken plasma. Addition of IGF-I or -II to a control pool of bovine plasma did not significantly alter control IGF-binding protein-2 values in a radioimmunoassay. Six nycthemeral periods, determined for three young bulls bled on two occasions, showed that IGF-binding protein-2 plasma levels were stable throughout the day; two or three samples were sufficient to characterize the animal. Cows treated with recombinant bovine somatotropin (bST) had significantly lower serum levels of IGF-binding protein-2 than did control cows. Furthermore, IGF-binding protein-2 levels were dramatically increased at the onset of lactation. This radioimmunoassay for bovine IGF-binding protein-2, which enables quantitative assessment of IGF-binding protein-2 concentration in cattle, confirmed that IGF-binding protein-2 concentrations are depressed by administration of bST, enhanced after calving, and showed absence of diurnal variation.

Key Words: bovine insulin-like growth factor-binding protein-2 • radioimmunoassay

Submitted on March 15, 1999
Accepted on October 1, 1999




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