The effects of energy source and tryptophan on the rate of protein synthesis and on hormones of the entero-insular axis in the piglet

Abstract

The present experiment was designed to study the influence of dietary energy source (fat or carbohydrate) and tryptophan (TRP) on protein synthesis and plasma insulin concentrations in the piglet. Six dietary regimens, based on either a high-fat (F) or a high-carbohydrate (C) diet with three levels of TRP (deficient, 1; adequate, 2; excess, 3), were used. Fractional protein synthesis rate (ks; % per d) was measured in the liver,Longissimus dorsi(LD),Semitendinosus(ST), skin, femur, brain, pancreas, stomach, mucosa of the duodenum and jejunum, and the whole body, using a‘flooding dose’of3H-phenylalanine. Mean integrated insulin, gastric inhibitory polypeptide (GIP) and glucose concentrations were higher after the C diets compared with the F diets, TRP supplementation globally augmentedkslinearly in the liver, ST, skin and whole body, while it had quadratic effects in the LD (kshighest in the TRP-adequate diet groups) and jejunal mucosa (kslowest in the TRP-adequate diet groups). Pancreatickswas increased by TRP addition up to a plateau.kswas highest after the F diets in the digestive tissues while in the skin and LDkswas highest after the C diets. Fasting concentrations of gluconeogenic amino acids were lower (and urea higher) with the F than the C diets, suggesting their use as precursors for glucose synthesis. In conclusion, we have confirmed the depressive effects of TRP deficiency onks, RNA activity and growth. We could not establish a relationship between plasma insulin and muscleks. This may be related to the way in which we manipulated plasma insulin concentrations.