A novel method for the extraction of sheep insulin-like growth factors-I and -II from plasma prior to radioimmunoassay.
The measurement of insulin-like growth factors (IGFs) in plasma is complicated by the presence of high-affinity IGF-binding proteins (IGFBPs). Consequently, the IGFBPs need to be removed or their IGF-binding effects need to be neutralized prior to assaying samples for IGFs. It was observed that IGFs but not IGFBPs from sheep plasma bind to the size-exclusion gel Sephacryl S-100 HR at a low pH and that the IGFs can subsequently be eluted off at a neutral pH. From this observation a convenient method was developed for the extraction from plasma of ovine (o) IGF-I and -II free from detectable IGFBPs with close to 100% recovery. When assayed in homologous sheep IGF-I and -II radioimmunoassays the Sephacryl-extracted plasma samples gave dose-response curves which were parallel to purified oIGFs. Furthermore, the results obtained by Sephacryl extraction were highly correlated with those found by the established Sephadex G-75 extraction procedure.
Moore
L G
LG
AgResearch, Wallaceville Animal Research Centre, Upper Hutt, New Zealand.
Mylek
M E
ME
D000818:Animals; D002352:Carrier Proteins / Q000032:analysis; D002850:Chromatography, Gel / Q000379:methods*; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D007335:Insulin-Like Growth Factor II / Q000032:analysis*; D011863:Radioimmunoassay; D012756:Sheep / Q000097:blood*; D013002:Somatomedins / Q000032:analysis
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II