Absorption of L-carnosine, L-methionine, and L-methionylglycine by isolated sheep ruminal and omasal epithelial tissue1

The absorption of carnosine, methionine, and methionylglycine (using 35S-methionine and 35S-methionylglycine as representative markers) across ruminal and omasal epithelia collected from four (carnosine) and seven sheep (methionine and methionylglycine) were studied using parabiotic chambers that were repeatedly sampled over a 240-min incubation. The quantity of all substrates transferred was linearly (P < .01) dependent on initial substrate concentration and time. More (P < .01) carnosine, methionine, and methionylglycine was transferred across omasal than across ruminal epithelia. Carnosine was absorbed across both tissues without hydrolysis. Methionylglycine was transferred intact across both tissues. A greater (P < .01) quantity was hydrolyzed by omasal than by ruminal epithelia, after 240 min of incubation. Greater (P < .06) quantities of methionine and methionylglycine accumulated in ruminal tissue after 240 min. Total absorption of methionine and methionylglycine did not differ within tissues, but total absorption of both substrates was greater (P < .01) by omasal tissues. There was little evidence for saturable absorption. These results indicate that omasal epithelial tissue possesses a greater ability to absorb both free and peptide-bound amino acids than does ruminal epithelial tissues.