Insulin-like growth factors and insulin-like growth factor binding proteins in porcine serum and milk throughout lactation.
IGF-I, IGF-II, and IGF binding proteins (IGFBP) were characterized in porcine serum, colostrum, and milk on d 1-28 postpartum. IGF-I and -II were measured by heterologous RIA. Serum IGFBP were characterized by Western ligand blotting and milk IGF binding activity by [125I]-IGF binding assay. IGF-II accounted for 70-85% of serum IGF and rose 2-fold between d 1 and d 28. Serum IGF-I was unaffected by duration of lactation. Milk IGF-II concentrations were higher than IGF-I concentrations on d 1-7 postpartum. After d 10, milk IGF-I and IGF-II contents were not significantly different. Serum contained IGFBP with M(r) of 43, 39, 34, 28, and 24 kD. Over the course of lactation, the 43- and 39-kD bands increased, the 24-kD band decreased, and the 34- and 28-kD bands were unchanged. Milk IGF binding activity increased between d 1 (28%) and d 3 (44%), then declined until d 28 (7%). Serum and milk were separated by isoelectric focusing into 20 fractions, across a gradient from pH 3 to 10, that were screened for IGFBP by Western ligand blotting. Milk contained six IGFBP of similar M(r) as serum IGFBP; however, the relative amounts of the IGFBP and their apparent isoelectric points differed. In conclusion, porcine milk contains both IGF-I and -II, with IGF-II predominating. Several IGFBP with similar M(r) as those found in serum are present in milk. IGF peptide concentrations were highest in prepartum secretions and colostrum, whereas IGF binding activity peaked on d 4 of lactation.
Department of Food Science, University of Illinois, Urbana 61801.
S M
SM
Donovan
L K
LK
McNeil
R
R
Jiménez-Flores
J
J
Odle
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000097:blood* / Q000737:chemistry / Q000378:metabolism*; D003126:Colostrum / Q000378:metabolism; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D007774:Lactation / Q000097:blood* / Q000378:metabolism*; D008892:Milk / Q000378:metabolism*; D008894:Milk Proteins / Q000378:metabolism; D008970:Molecular Weight; D011247:Pregnancy; D013002:Somatomedins / Q000378:metabolism*; D013552:Swine; D013997:Time Factors
D002352:Carrier Proteins; D008894:Milk Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II