Relationship between riboflavin intake and excretion in female rats after weaning of the litter.

Six groups of female rats which gave birth to offspring of 8 young (or adjusted to 8) were fed diets containing 2, 4, 6, 8, 12, or 16 mg of riboflavin per kg of dry matter. Seventeen days after birth, young were withdrawn from the mothers and these were placed in metabolic cages and excreta (urine and feces) were daily collected for 17 days. The activity coefficient of blood glutathione reductase was 1.45 in 17 days old young of group 2 whereas it was 1.12 in young of other groups. The coefficient was 1.09 in female rats at the end of the experiment. 5 and 6 days after excreta collection began urinary excretion of riboflavin reached a peak in females of groups 4 to 16. At the end of the experiment, females which were fed 8 mg of riboflavin/kg or more had an urinary excretion of the vitamin which reached a plateau at 50 micrograms/day. On the other hand fecal excretion of riboflavin markedly increased as the intake did. Data suggested that the intestinal absorption of riboflavin is limited but also that the requirement of riboflavin in lactating rats is 8 mg/kg of diet whereas it is 2 mg/kg for maintenance.