Insulin-like growth factor-I and its association with binding proteins in bovine milk.
Immunoreactive insulin-like growth factor-1 (IGF-I in bovine milk was quantified. IGF-I was principally assoication with an approximately 45 kDa binding protein. In addition, a small fraction of IGF-I occurred at a molecular weight approximately the same as that of unbound IGF-I. Available binding sites existed on the approximately 45 kDa binding protein. Bound IGF-I was readily dissociated from binding protein by acid treatment. When IGF-I was estimated in milk obtained from primiparous and multiparous cows, mutiparous cows had a higher concentration (40 nmol/1) [corrected] at parturition than primiparous cows (19.2 nmol/1) [corrected]. By day 2 of lactation, IGF-I concentrations were 30 and 50% of initial estimates for multiparous and primiparous cows respectively. the final IGF-I concentration, on day 56 of lactation, was 4.5 nmol/1 [corrected] for combined parity groups. At parturition in multiparous cows, the mass of IGF-I was estimated at 183 and 157 nmol [corrected] for blood and milk pools respectively. Milk, therefore, represents a substantial pool of IGF-I in the cow. The mechanism of the appearance of IGF-I in bovine milk is unknown.
Campbell
P G
PG
Department of Dairy and Animal Science, Pennsylvania State University, University Park 16802.
Baumrucker
C R
CR
D000818:Animals; D002352:Carrier Proteins / Q000097:blood / Q000378:metabolism*; D002417:Cattle; D003126:Colostrum / Q000378:metabolism; D005260:Female; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000097:blood / Q000378:metabolism*; D008892:Milk / Q000378:metabolism*; D010298:Parity; D013002:Somatomedins / Q000378:metabolism*; D013997:Time Factors
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I