[Effect of methionine supplementation of a diet low in riboflavin and at 2 levels of protein on metabolism of riboflavin in the lactating rat].

Lactating female rats were fed diets A or B containing 18 and 12% of casein respectively, or similar diets but supplemented with 0.4% of methionine (diets AM or BM). The animals and their pups were sacrificed at the 18th day of lactation. Control non lactating female rats fed the same diets for the same period of time were also sacrificed. Total riboflavin and its various forms (flavin adenin dinucleotide, flavin mononucleotide + free riboflavin) were measured in various tissues as well as in the milk which was collected from the stomach of the pups after a time controlled suck. In the lactating females fed diets A and B as well as in the control animals fed the same diets the concentrations of riboflavin and of its various forms in plasma, liver and carcass are unchanged. However in group B, they are higher in milk and in tissues of the pups. These results seem to be due to a decrease in food intake by the lactating females fed diet B which results in a decrease in milk production which in turn induces a lower growth rate of the pups although the riboflavin consumption by the latter is unchanged. Addition of methionine to the diet B (diet BM) induces the same effects as diet A which contains the highest amount of proteins but addition of methionine to the diet A (diet AM) has no further incidence. Therefore the present study has not revealed any direct effect of methionine on riboflavin metabolism in lactating female rats and their pups since the effects are similar to an increase of the total protein level in the diet. In both cases they seem to be simply related to an increase of the food consumption.