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Growth and Riboflavin Status of Rats Fed Different Levels of Protein and Riboflavin^1,2,

Department of Human Nutrition, College for Human Development, Syracuse University and Department of Medicine, State University of New York Upstate Medical Center, Syracuse, NY 13210

The relationship between riboflavin and protein utilization was studied in 5-week-old male Sprague-Dawley rats, by using a factorial design with three levels of riboflavin (8, 16 and 24 µg per rat per day) and protein (1.0, 1.6 and 2.2 g casein per rat per day) in a 9-week experiment. With the lowest level of casein, protein intake was growth limiting, and the level of riboflavin intake had no effect on either weight gain or liver nitrogen retention. With the two higher levels of casein, both weight gain and liver nitrogen retention increased with riboflavin intake, but 24 µg riboflavin per day was inadequate for maximal utilization of nitrogen from 2.2 g casein. Neither protein nor riboflavin intake affected the concentration of liver nitrogen per gram of fresh tissue. Increasing the protein intake from 1.0 to 1.6 g increased riboflavin retention in the liver, but additional protein had no further effect. Liver and muscle (gastrocnemius) riboflavin concentrations, as micrograms per gram wet tissue, increased with riboflavin intake. At the two higher intakes of riboflavin, tissue riboflavin levels decreased and the erythrocyte glutathione reductase activity coefficients (EGR-AC) increased with protein intake. These findings are consistent with the view that the effect of protein on riboflavin requirement is related to the rate of growth and not to protein intake, per se.

KEY WORDS: • riboflavin-protein interdependence • riboflavin status • erythrocyte glutathione reductase activity coefficient

¹ Supported, in part, by the National Institutes of Health Biomedical Research Support Grant Program, grant no. S07 RR07068-15, to Syracuse University and S07 RR05402-19 to the State University of New York, and by the Hendrick's Fund, the Research Foundation of the State University of New York Upstate Medical Center.

² Presented, in part, at the Annual Meeting of the Federation of American Societies for Experimental Biology, Atlanta, Georgia, 1981. Fed. Proc. 40, 914, 1981.

Manuscript received 12 April 1982.