Effect of gastric inhibitory polypeptide on bovine fat metabolism

Gastric inhibitory polypeptide (GIP), a hormone secreted by the gastrointes tinal tract in response to nutrient absorption, exerts anabolic effects on adipose tissue in some species. Cattle fed on grass silage diets tend to de posit more fat than animals fed on dried forages. We investigated the effec t of diet on blood GIP concentrations in cattle. Plasma concentrations tend ed to be higher in cattle fed grass silage alone or supplemented with fishm eal (0.61 ng/ml) compared with animals fed dried grass/barley (0.43 ng/ml, P > 0.1) and were inversely correlated with plasma insulin concentrations ( r = - 0.727, P < 0.01). The effects of increasing concentrations (0, 0.1, 1 .0, 10.0 nM) of GIP and glucagon-like peptide-1 (GLP-1) on basal and insuli n-stimulated lipogenesis in bovine adipose tissue in vitro were investigate d after 4 and 24 h of incubation. No conclusive effects were obtained with either peptide. Subsequently, the effect of exogenous administration of GIP (10 or 50 ng/kg liveweight per min) on whole-body fat metabolism was inves tigated in two steers in vivo. Plasma concentration and flux rate of palmit ate was increased by GIP only at the higher infusion level suggesting lipol ysis and possibly fatty acid re-esterification was stimulated at high conce ntration. We conclude that although gut peptides may regulate nutrient util isation, it is unlikely that they play a major role in promoting fat accret ion in cattle. However, the small number of animals used in these studies i ndicates the need for caution and further studies are warranted. (C) 1999 E lsevier Science Inc. All rights reserved.