Liver and kidney nitrogen uptake in rats fed beans enriched with 15nitrogen through (15NH4)2SO4 used as soil fertilizer.

This study was conducted to determine the incorporation of 15nitrogen (15N) into liver and kidney of a group of rats (N = 17) fed a mixture of cooked rice and beans for 4 weeks. The beans (Phaseolus vulgaris), grown in soil cultivated with (15NH4)2SO4, had 1.5% 15N enrichment. Three or four rats were sacrificed weekly and a control group (N = 13) received an isonitrogen and isocaloric reference casein diet. The amount of nitrogen transferred from the beans to the liver at the end of the first, second, third and fourth weeks was 17, 11, 27 and 29% of the total nitrogen, respectively. For the kidney, the respective values were 10, 9, 25 and 27% of the total nitrogen. The total nitrogen content of the liver and kidney of rats receiving the reference casein control diet was similar to that of the rice/beans animals. Weight gain was similar for the two groups, indicating the well-balanced biological value of the experimental diet. The present study shows that it is possible to monitor 15N incorporation into beans and subsequently into rat liver and kidney, in contrast to classical methods for protein metabolism evaluation which measure only total body nitrogen intake and excretion or weight gain.