Abstract

The somatotrophic axis has a major effect on lean growth in a number of species. GH, the main hormone of the somatotrophic axis, is controlled by growth hormone releasing hormone and somatostatin. GH can act directly on fat by increasing lipolysis, but its main anabolic effects are on muscle and bone via the Insulin like growth factor-I (IGF-I). IGF-I stimulates amino acid uptake into muscle in vitro but does not necessarily promote growth if given in vivo. The reason for this is that GH is now considered to control circulating IGF- I as well as local tissue production of IGF-I, the dual effector theory. This theory proposes that GH not only controls IGF-I production but controls differentiation of cells so that they can respond to the mitogenic effects of IGF-I. Insulin is another anabolic hormone which is affected by GH. Insulin, unlike GH, stimulates fat deposition, although it also increases protein accretion. The manipulation of the growth hormone axis by immunological procedures, selection or genetic engineering may provide an economic way for NZ farmers to increase the production of lean meat.

J, Hodgson

Proceedings of the New Zealand Society of Animal Production, Volume 50, , 29-34, 1990