Endogenous lysine flow at the distal ileum of the protein‐fed rat: Investigation of the effect of protein source using radioactively labelled acetylated lysine or lysine transformed to homoarginine

Abstract

AbstractThe study aimed to determine if the source of purified dietary protein influenced endogenous lysine flow at the terminal ileum of the growing rat. Partially guanidinated gelatin and isolated soya bean protein based diets, containing chromic oxide as an indigestible marker, were given to 225‐g liveweight rats. The endogenous flow of lysine at the terminal ileum was then determined indirectly, based on the absorption of homoarginine, after sampling of ileal contents at slaughter. Endogenous lysine flow was also determined by reference to chromium levels in sampled ileal digesta, after feeding rats either gelatin or isolated soya bean protein or casein based diets in which some of the lysine had been acetylated with [14C]‐acetic anhydride. The [14C] acetylated lysine was used to distinguish between lysine of dietary and endogenous origin. Mean endogenous ileal lysine flows were 426 and 442 μ g−1 dietary freeze dry matter intake for the guanidinated gelatin (n=6) and soya bean (n = 6) treatments, respectively, and there was no significant (P>0.05) effect of protein source on endogenous flow. Nor did there appear to be any effect of dietary protein source on endogenous ileal lysine flow when measurement was based on the radio‐actively labelled acetylated lysine. The data, considered together, indicate no effect of the source of dietary protein per se on endogenous ileal lysine flow in the rat when purified proteins were given over a short (8‐h) time period. The mean true ileal digestibility coefficients for dietary lysine (0.897, 0.904, 0.926, 0.971, 0.916; acetylated gelatin, guanidinated gelatin, guanidinated soya bean, acetylated soya bean, acetylated casein, respectively) indicated a high degree of absorption of lysine before the end of the ileum in the growing rat.