Mechanism of insulin action on glucose metabolism in ruminants
This review presents a brief overview on the mechanism of insulin action on glucose metabolism at the molecular basis in ruminants. For ruminants, an exact mechanism of insulin on glucose metabolism is still rudimentary, but it is clear that originally, if not all, the mechanism of insulin action in ruminants was the same as in other species. Like non-ruminants, the insulin-sensitive glucose transporter GLUT 4 is thought to be a key-protein in the control of glucose uptake and metabolism in ruminants, and insulin regulates glucose transport by stimulating the translocation of GLUT 4 from an intracellular membrane pool to the plasma membrane in adipocytes and muscles. Moreover, insulin-induced GLUT 4 translocation is activated through the common intracellular signaling pathway of insulin phosphatidylinositol 3-kinase (PI3-kinase) signaling pathway rather than the mitogen activated protein kinase (MAP kinase)-dependent signaling pathway. However, GLUT 4 mRNA and protein, and insulin-induced GLUT 4 translocation on adipocytes and muscles in ruminants are lower than those in rodents and human subjects. Furthermore, insulin-induced PI3-kinase activation is reduced concomitantly with the lower content of insulin receptor substrate-1 (IRS-1) in ruminants. In spite of normal status, a resistance to the stimulatory action of insulin on glucose metabolism in ruminants as compared to non-ruminants may be due to, at least in part, the lower content of GLUT 4 and the lower capacity of insulin signal transduction, resulting to the lower glucose transport activity.
Document Type: Review Article
Affiliations: Faculty of Agriculture, Shinshu University, Minamiminowa-mura, Nagano-ken, Japan
Publication date: 2002-12-01