title: Measurement of dimeric inhibin in porcine serum: evidence for low concentrations and existence of binding proteins.
abstract: An immunoradiometric assay and serum extraction procedure were developed to measure dimeric inhibin in porcine serum with minimal interference by putative inhibin-binding proteins. Assay sensitivity was 50 pg/tube, and it incorporated antibodies against the N-terminal region of inhibin's alpha-subunit, alpha-(1-25)-Ab, and against the C-terminal region of inhibin's beta A-subunit. To determine whether inhibin-binding proteins were present in porcine serum, serum was incubated with [125I]-recombinant human (rh)-inhibin and then chromatographed by gel filtration. Radioiodinated rh-inhibin was associated with protein(s) > 600 kDa. Radioiodinated rh-inhibin also was incubated with alpha 2-macroglobulin, an inhibin-binding protein in human and rat serum. Elution profiles were similar for serum and alpha 2-macroglobulin. Serum- and alpha 2-macroglobulin-[125I]rh-inhibin complexes dissociated upon exposure to 8 M urea. Porcine serum was treated with urea, after which inhibin was isolated and concentrated. The recovery of rh-inhibin added to starting serum was 28%. Concentrations of endogenous dimeric inhibin were < 28 pg/ml in serum collected from sows at random stages of the estrous cycle and were < 21 pg/ml in serum collected from sows 2 d postweaning. Results demonstrate that 1) concentrations of dimeric inhibin are low in porcine serum, and 2) an inhibin-binding protein(s), consistent with alpha 2-macroglobulin, is present in porcine serum.
authors.affiliation: Department of Animal Science, University of Minnesota, St. Paul 55108, USA.
authors.forename: R L
authors.initials: RL
authors.lastname: Meyer
authors.forename: J E
authors.initials: JE
authors.lastname: Wheaton
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000097:blood*; D006801:Humans; D015592:Immunoradiometric Assay; D007265:Inhibins / Q000097:blood* / Q000302:isolation & purification; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D011994:Recombinant Proteins / Q000097:blood; D013552:Swine / Q000097:blood*; D000511:alpha-Macroglobulins / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D000511:alpha-Macroglobulins; D007265:Inhibins