Effect of dietary stable isotopic ratios of carbon and nitrogen on the extent of their incorporation into tissues of rats

This study was conducted to investigate the effect of different dietary ratios of C-13 to C-12 or N-15 to N-14 on their relative incorporation into tissues. Eighty male rats were used in two 21-day feeding trials in which they were fed diets with either high delta C-13 levels (delta C-13=-13.89% and delta N-15 = 2.37% in experiment 1 and delta C-13=-19.34% and delta N-15 = 4.73% in experiment 2) or low delta C-13 levels (delta C-13=-17.90% and delta N-15 = 3.08% in experiment 1 and delta C-13=-21.76% and delta N-15 = 0.53% in experiment 2), meanwhile, the dietary delta N-15 levels were designed to two ranks. Blood, liver, adipose and muscle tissues were collected on day 0, 3, 7, 14, and 21 for determination of C-13, C-12, N-15 and N-14 isotopes. Rat growth rate, antioxidant capacity and metabolic parameters were also assessed. The results indicate that adipose tissue tend to deplete C-13 before the stable isotopic ratios achieved final equilibrium. Therefore, feeds with different isotopic signatures had different incorporation rates into tissues. Low dietary 13 C levels decreased tissue delta C-13 values whereas high dietary C-13 levels did not alter tissue delta C-13 values during the 21-d experiment. Blood delta N-15 values were a reliable parameter in assessing the relative contribution of dietary nitrogen to tissues. This study revealed a relationship between dietary isotopic signatures and their incorporation rates into rat tissues. However, more studies are needed to illustrate the mechanism through which dietary isotopic ratios influence the extent of isotopic incorporation into the tissues.