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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.

Respectualy ten and twenty-two months old rats, fed an equilibrated diet, were given daily and for one month an extra supplementation of thiamine, riboflavin and vitamin B6 in drinking water. Control animals of the same age were fed identical diets but without vitamin extra supplementation. Vitamin contents of organs (liver, heart, kidneys, spleen, lungs, brain) were determined in order to evaluate both the influence of aging and of vitamin supplementation. Twenty-three months old rats show lower values of thiamin contents (except in liver and brain), riboflavin contents (except in heart and spleen) and vitamin B6 contents (except in heart, lungs and brain) than younger rats. Vitamin extra-supplementation reduces some of these differences: thiamine contents in heart, kidneys and spleen, riboflavin contents in brain, vitamin B6 contents in kidneys and spleen. In all other cases, the extra-supplementation has no effect. Therefore, it seems that the decrease in vitamin contents in organs of old rats is, in many cases an unavoidable consequence of aging.

Nine and twenty-one months old rats fed a balanced diet were given for 5 weeks an extra supplementation in thiamine, riboflavin and vitamin B6. Control animals were given the same diet but without vitamin extra supplementation. Fecal and urinary vitamin excretions were determined during this 5 weeks period. They were shown to be less important in older rats than in younger ones. Influence of aging and vitamin supplementation on the vitamin contents of organs and tissues were studied on these animals: previous results were confirmed [see LECLERC, Ann. nutrit, Aliment., 1976, 30, 10--25]. From these results and others published elsewhere, it is conclused that in older animals there could be an increased intestinal destruction of the above mentionned vitamin although changes in vitamin metabolism can be involved too.