FUEL METABOLISM IN GROWTH HORMONE-DEFICIENT ADULTS

Apart from being a stimulator of longitudinal growth, growth hormone ( GH) regulates fuel metabolism in children and adults. A halfmark is mo bilization of lipids, which involves an inhibition of lipoprotein lipa se activity in adipose tissue and activation of the hormone sensitive lipase. Suppression of basal glucose oxidation and resistance to insul in are other important effects. This may cause concern during GH subst itution in GH-deficient adults, some of whom may present with insulin resistance due to concomitant abdominal obesity. However, there are da ta to suggest that the GH-induced reduction in fat mass and increase i n lean body mass may offset the insulin antagonistic actions of the ho rmone. The nitrogen-retaining effects of GH seem to involve a direct s timulation of protein synthesis in addition to secondary effects such as generation of insulin-like growth factor-I (IGF-I), hyperinsulinemi a, and promotion of lipolysis. Thus, during periods of substrate afflu ence, GH acts in concert with insulin and IGF-I to promote protein ana bolism. Postabsorptively, GH is primarily lipolytic and thereby indire ctly protein-sparing. This effect becomes further accentuated with mor e prolonged fasting. In that sense, GH is unique by its preservation o f protein during both feast and famine. These fuel metabolic effects a dd merit to the principle of GH substitution in hypopituitary adults. Copyright (C) 1995 by W.B. Saunders Company.