THE EFFECTS OF ENERGY-SOURCE AND TRYPTOPHAN ON THE RATE OF PROTEIN-SYNTHESIS AND ON HORMONES OF THE ENTEROINSULAR AXIS IN THE PIGLET

The present experiment was designed to study the influence of dietary energy source (fat or carbohydrate) and tryptophan (TRP) an protein sy nthesis and plasma insulin concentrations in the piglet. Six dietary r egimens, based on either a high-fat (F) or a high-carbohydrate (C) die t with three levels of TRP (deficient, 1; adequate, 2; excess, 3), wer e used. Fractional protein synthesis rate (k(s); % per d) was measured in the Liver, Longissimus dorsi (LD), Semitendinosus (ST), skin, femu r, brain, pancreas, stomach, mucosa of the duodenum and jejunnm, and t he whole body, using a 'flooding dose' of H-3-phenylalanine. Mean inte grated insulin, gastric inhibitory polypeptide (GIP) and glucose conce ntrations were higher after the C diets compared with the F diets, TRP supplementation globally augmented k(s) linearly in the Liver, ST, sk in and whole body, while it had quadratic effects in the LD (k(s) high est in the TRP-adequate diet groups) and jejunal mucosa (k(s) lowest i n the TRP-adequate diet groups). Pancreatic k(s) was increased by TRP addition up to a plateau. k(s) was highest after the F diets in the di gestive tissues while in the skin and LD k(s) was highest after the C diets. Pasting 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 th e depressive effects of TRP deficiency on k(s), RNA. activity and grow th. We could not establish a relationship between plasma insulin and m uscle k(s). This may be related to the way in which we manipulated pla sma insulin concentrations.