Uptake and retention in suckling rats of (51)Chromium fed with human milk or infant formulas

Optimum concentration of Cr for infant formulas has not been established. Such components as soy protein or supplemental Fe could influence absorption and retention. Suckling rat pups were used to evaluate the influence of three commercial formulas and human milk, all of which had been incubated with (CrCl3)-Cr-51 for 1 h, on the uptake and retention of the added Cr-51. After fasting 3 h, the pups were intubated with a single dose of 25 mu Ci (CrCl3)-Cr-51 in either a cow's milk-based formula, an Fe-supplemented cow's milk-based formula, a soy-based formula, or human milk. Six hours later, Cr-51 was counted in five organs, thymus, blood, and total urine. Absorption of Cr-51 was low. At 6 h, percent Cr-51 in blood was <0.2% of the dose, and total Cr-51 excretion in urine was <1.8%. The uptake and retention of Cr-51 and its concentration in any of the organs, thymus, blood, and urine were not influenced by different types of formula or by human milk.