Metabolic actions of pituitary growth hormone. I. Inhibition of acetyl CoA carboxylase by human growth hormone and a carboxyl terminal part sequence acting through a second messenger.

Evidence is presented showing that human growth hormone (hGH) and its part sequence hGH 172-191 inhibit acetyl CoA carboxylase and hence fatty acid synthesis by interacting with adipocyte and hepatocyte plasma membranes, resulting in the release of a relatively non-polar second 'messenger'. This second 'messenger' inhibits the enzyme in a soluble fraction by increasing its phosphorylation. It appears that growth hormone requires some modification prior to demonstrating this activity, as it is active in intact cells and unfractionated homogenates but has no activity in 'messenger release' from purified membrane fractions. The relations of these actions to the in vivo effects of hGH are discussed.