Identification of human semen insulin-like growth factor-I/somatomedin-C immunoreactivity and binding protein.
Human seminal plasma (SP) samples have been tested for insulin-like growth factor-I/somatomedin-C (IGF-I/SM-C) immunoreactivity. Gel chromatography of SP at neutral pH indicated that all immunoreactive IGF-I/SM-C was present at a higher molecular weight than the free peptide from plasma, while in 1 M acetic acid, a major peak of immunoreactivity was seen at an apparently lower molecular weight than the free peptide, together with a peak with molecular weight about 40 000. This latter peak contained a binding protein which, on Scatchard analysis, was shown to have a single class of binding site, Ka = 1.2 X 10(10) L/mol. The low molecular weight peak material was displaced from monoclonal and polyclonal IGF-I/SM-C antibodies parallel to standard preparations. Its elution on gel chromatography later than plasma IGF-I/SM-C was shown by re-chromatography to be due to physical retardation on the column, rather than a lower molecular weight. As acid-ethanol extraction of SP samples failed to remove binding activity, samples from patients were all subjected to acid gel chromatography before assay. The mean IGF-I/SM-C content in 5 normal men was 20.7 +/- 3.7 (SD) ng/ml while that for 4 azoospermic subjects was 9.2 +/- 3.7 ng/ml. A hyposomatotrophic subject with normal sperm density and low serum IGF-I/SM-C had an SP IGF-I/SM-C value in the normal range. This study indicates that human semen contains protein-bound immunoreactive IGF-I/SM-C which is at least in part of testicular origin, and apparently not growth hormone-dependent.
D000328:Adult; D002850:Chromatography, Gel; D006801:Humans; D007328:Insulin / Q000032:analysis* / Q000096:biosynthesis / Q000276:immunology; D007334:Insulin-Like Growth Factor I; D008297:Male; D008970:Molecular Weight; D009845:Oligospermia / Q000378:metabolism; D010452:Peptide Biosynthesis; D010455:Peptides / Q000032:analysis* / Q000276:immunology; D011485:Protein Binding; D012661:Semen / Q000032:analysis*; D013002:Somatomedins / Q000032:analysis* / Q000096:biosynthesis / Q000276:immunology; D013737:Testis / Q000378:metabolism
D007328:Insulin; D010455:Peptides; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I