title: Increased degradation of insulin-like growth factor-I in serum from feed-deprived steers.
abstract: Severe feed restriction decreases serum insulin-like growth factor I (IGF-I) concentration in animals, and this decrease is thought to be due to reduced IGF-I production in the liver. The objective of this study was to determine whether feed deprivation also increases degradation of serum IGF-I and serum levels of IGF binding protein 3 (IGFBP-3) and acid-labile subunit (ALS), which inhibit IGF-I degradation and increase IGF-I retention in the blood by forming a ternary complex with IGF-I, in cattle. Five steers had free access to pasture, and another five were deprived of feed for 60 h. Serum concentration of IGF-I and liver abundance of IGF-I mRNA at the end of the 60-h period were 50% and 80% lower, respectively, in feed-deprived steers than in fed steers. Less (125)I-labeled IGF-I remained intact after a 45-h incubation in sera of feed-deprived steers than in sera of fed steers, suggesting that serum IGF-I is more quickly degraded in feed-deprived animals. Serum levels of IGFBP-3 and ALS were decreased by 40% and 30%, respectively, in feed-deprived steers compared with fed steers. These decreases were associated with more than 50% reductions in IGFBP-3 and ALS mRNA in the liver, the major source of serum IGFBP-3 and ALS. Taken together, these results suggest that feed deprivation reduces serum concentration of IGF-I in cattle not only by decreasing IGF-I gene expression in the liver, but also by increasing IGF-I degradation and reducing IGF-I retention in the blood through decreasing IGFBP-3 and ALS production in the liver.
authors.affiliation: Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0306, United States.
authors.forename: Miaozong
authors.initials: M
authors.lastname: Wu
authors.forename: Aihua
authors.initials: A
authors.lastname: Wang
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Bernard
authors.forename: John B
authors.initials: JB
authors.lastname: Hall
authors.forename: William E
authors.initials: WE
authors.lastname: Beal
authors.forename: R
authors.initials: R
authors.lastname: Michael Akers
authors.forename: Yves R
authors.initials: YR
authors.lastname: Boisclair
authors.forename: Honglin
authors.initials: H
authors.lastname: Jiang