Uptake and retention in suckling rats of51chromium 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 with⁵¹CrCl₃ for 1 h, on the uptake and retention of the added⁵¹Cr. After fasting 3 h, the pups were intubated with a single dose of 25 μCi⁵¹CrCl₃ 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,⁵¹Cr was counted in five organs, thymus, blood, and total urine. Absorption of⁵¹Cr was low. At 6 h, percent⁵¹Cr in blood was <0.2% of the dose, and total⁵¹Cr excretion in urine was <1.8%. The uptake and retention of⁵¹Cr and its concentration in any of the organs, thymus, blood, and urine were not influenced by different types of formula or by human milk.