Determination of circulating levels of insulin-like growth factor II (IGF-II) in swine.
A heterologous radioimmunoassay system was developed for the determination of circulating IGF-II concentrations in swine. The assay utilized a monoclonal antibody against human IGF-II (Amano Intl. Ez, VA) and bovine IGF-II (Monsanto Co., MO) as the cold standard and iodinated ligand. Serial dilutions of acid-ethanol extracted normal swine sera resulted in a curve which was parallel to the bovine IGF-II standard curve. Recovery of unlabeled standard added to extracted swine sera was 101%. Neither IGF-I nor insulin were capable of cross-reacting in this assay at levels up to 100-fold excess. Using this assay, serum IGF-II levels were determined to be significantly lower when subnormal growth hormone (GH) levels existed such as in hypophysectomized swine. However, in contrast to serum IGF-I concentrations, supranormal levels of porcine GH (pGH) did not elevate serum IGF-II concentrations after 13 wk of treatment in 25 kg hogs (initial body wt). In addition, serum IGF-II levels were reduced in fasted swine, despite a significant increase in circulating GH concentrations. Thus, although normal concentrations of GH are required for maintenance of physiological levels of IGF-II in swine, the mechanism for stimulation of IGF-II secretion is less GH-dependent than IGF-I.
Buonomo
F C
FC
Monsanto Company, Animal Sciences Division, St. Louis, MO 63198.
Grohs
D L
DL
Baile
C A
CA
Campion
D R
DR
D000818:Animals; D013006:Growth Hormone / Q000097:blood; D007016:Hypophysectomy; D007334:Insulin-Like Growth Factor I / Q000097:blood; D007335:Insulin-Like Growth Factor II / Q000097:blood*; D008297:Male; D011863:Radioimmunoassay; D013002:Somatomedins / Q000097:blood*; D013552:Swine / Q000097:blood*
D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone