Investigation on the absorption of 14C-leucine and 15N-leucine in rats after feeding a fish meal diet in comparison with a gelatine diet

Albino rats received after nine days of adaptation to a fish meal diet in comparison with a gelatine diet 14C-U-L-leucine and 15N-L-leucine via a pellet made from the specific diet after food deprivation for 15 h. Thereafter, the animals consumed the non-labelled experimental diet ad libitum. 30 min, and 1, 2, 4 and 8 h, resp., after intake of the labelled food, four rats at a time were sacrificed. The contents of the digestive tract and tissue samples were examined for 14C and 15N and their percentages in the TCA-soluble fraction determined. If these values are regarded as non-absorbed leucine, the 14C values obtained up to the four hour period of the experiment would be too high. Presumably, they are in the case of both diets simulated by other 14C metabolites which originate from the leucine catabolism and reach the intestinal lumen. Amino acids labelled with 15N should be preferred in studies on the absorption of amino acids because, in case of catabolization, the 15N aminogroup is excreted mainly as urea via urine. (author)