A casein hydrolysate does not enhance gut endogenous protein flows compared with intact casein when fed to growing rats

We studied the effect of dietary free peptides vs. peptides released naturally during digestion on gut endogenous nitrogen (N) flow (ENFL) and amino acid (AA) flow (EAAFL). Semisynthetic diets containing 110g/kg diet of the same casein, intact (C) or hydrolyzed (HC), were formulated with TiO2 as a dietary marker. Sprague-Dawley rats were fed the diets hourly (0800-1500 h) for 10 min each hour for 7 d. Rats received unlabeled diets for 6 d and N-15-labeled diets on d 7, whereby they were killed and digesta sampled (6 observations per group) along the intestinal tract. EAAFL and ENFL were determined by N-15-isotope dilution (ID) for C or by ID or after centrifugation and ultrafiltration ME) for HC. Ileal EAAFL and ENFL OD) were not enhanced with diet HC compared with diet C. The AA compositions (g/16 g N) of ileal ENFL did not differ between rats fed HC and C except for Asp, Phe, Tyr, and Ser, for which contributions were relatively lower (P < 0.05) for rats fed C. Ileal EAAFL and ENFL (HC) were considerably lower (P < 0.05) with ID than with UF, but flows of Gly, Phe, and His were similar, There was no stimulatory effect of dietary peptides from HC on endogenous ileal protein flow compared with C, but the result is tentative given the high degree of dietary N recycled within endogenous protein and which could have occurred at a differential rate between rats fed diets C and HC.