INFLUENCE OF INULIN ON UREA AND AMMONIA NITROGEN FLUXES IN THE RAT CECUM - CONSEQUENCES ON NITROGEN-EXCRETION

The effect of the addition of 15% chicory inulin on the nitrogen balance and the processes of N exchanges between blood plasma and the large intestine have been investigated in rats adapted to diets having a normal (15%) or high (45%) casein level. Inulin diets elicited a marked enlargement of the cecum, together with an acidification of the cecal content and an increase of the cecal volatile fatty acids pool. The net N balance was not affected by the various dietary conditions, but N digestibility was apparently depressed in rats fed inulin. This merely reflected a shift of N excretion from the renal to the intestinal site; this last effect was more marked in rats adapted to the normal protein level. Inulin depressed cecal ammonia only in rats adapted to the normal protein level. The balance between urea N transfer (blood plasma --> cecum) and ammonia N transfer (cecum --> blood plasma) was positive only in rats fed inulin, reflecting a net urea N retention in the cecum. In rats fed the inulin-45% casein diet, urea N transfer was very high, but very large amounts of N were reabsorbed as ammonia, suggesting a relatively poor incorporation of this N source in bacteria. The total concentrations of free amino acids in the cecum were significantly enhanced by inulin, but the cecal reabsorption of amino acids was quantitatively marginal. It appears that inulin is very effective in increasing fecal N excretion, concomitantly to depressed renal N excretion, without altering protein bioavailability. This shift seems more evident when the dietary protein level is moderate.