Infusion of soy and casein protein meals affects interorgan amino acid metabolism and urea kinetics differently in pigs

For routine evaluation of the quality of dietary protein. amino acid scorin g patterns were used. Evaluation of this pattern for soy and casein reveale d that these proteins are of almost equal quality. However, in vivo studies showed a large difference. To study the biological effects of meals with c asein and soy protein, the contributions of individual amino acids to net p rotein retention and amino acid kinetics in gut, liver and muscle in health y pigs were investigated. Isonitrogenous enteral nutrition, infused at a ra te of 10 mL.kg body wt(-1).h(-1) and consisting of maltodextrin (137 g/L) w ith added casein (53 g/L) or soy protein (68 g/L), was given to conscious, healthy female multicathetized pigs (20-22 kg, n = 12). A primed-constant i nfusion protocol with L-[ring-2,6-H-3]phenylalanine, L-[3,4-H-3]valine and [N-15-N-15]urea was used to measure aminoacid and urea kinetics in gut, liv er and muscle. Measurements were done postabsorptively and 2-6 h after init iation of the enteral nutrition. During the meal, appearance of amino acids into the portal vein and the uptake by the liver was lower with casein inf usion. Muscle uptake did not differ. Gut protein synthesis tended to be low er with soy infusion (P = 0.1). Liver protein synthesis and degradation wer e higher with casein infusion (P < 0.05), while in muscle, soy infusion sti mulated protein turnover (P < 0.05). In comparison to the postabsorptive co ndition, liver urea production was unchanged after casein infusion, while i t was significantly increased after soy infusion. These results suggest tha t the quality of soy protein is inferior to that of casein protein.