IGF-II is a peptide mitogen bearing sequence homology with proinsulin and IGF-I, another potent mitogenic agent. Although the exact role of IGF-II is unclear, it probably is important in perinatal growth regulation and, particularly, in organ differentiation. We have previously identified the presence of IGF-I in significant concentrations in bile from rats of varying postnatal ages (Kong, et al, Am J Phys. 268:R266, 1995) as well as the absence in bile of IGF-associated binding proteins. Bile from suckling (10d), weanling (30 d), and adult (60 d) rats was obtained in timed collections of 120 minutes and assayed for the presence of radioimmunoassayable IGF-II (RIA-IGF-II). Excretion rates were then also calculated as shown below and compared to previously obtained data regarding IGF-I. Data are presented as mean±SEM. [# animals=( )]. IGF-II Bile Conc. IGF-II Excr. Rate IGF-II Excr. Rate (ng/ml) (pg/gm/hr) (μg/d) Suckling 230±38 (4) 511±101 0.41±0.08 Weanling 117±24 (3) 879±293 3.0±1.0 Adult 47±7 (3) 111±12 1.22±0.1 Concentrations shown above are approximately 2X those of IGF-I in similarly aged rats. Bile derived IGF-II also reacted in a competitive binding assay with a crude preparation of rat liver membranes containing IGF-II (type 2) receptors. These findings suggest significant delivery of bioactive IGF-II into the small bowel of rats at all ages studied. Lastly, in contrast to IGF-I, which has been shown to enter bile, at least in part, from blood, radiolabelled IGF-II injections in suckling rats were not associated with delivery into the bile, suggesting that bile IGF-II is wholly derived from hepatic production.
|Original language||English (US)|
|Journal||Journal of Investigative Medicine|
|State||Published - 1996|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)