Dietary Protein and Utilization of Carotene or Retinyl Acetate in Rats

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Abstract
Interaction of dietary protein with different sources of vitamin A was examined. In the first experiment, the effect of time on the utilization of a fixed dose of carotene in young rats fed diets with 10, 20 or 40% protein was determined. As the protein level was raised from 10 to 20% of the diet, hepatic retinol increased significantly at each weekly interval in a 28-day experimental period; but a refeeding period exceeding 21 days was required before an enhancing effect of feeding 40 versus 20% protein could be demonstrated. The second experiment dealt with the utilization of adequate, moderately high and high levels of either carotene or retinyl acetate in the presence of varying amounts of protein. Usually, utilization of carotene, when evaluated by the combined hepatic and renal deposits, was linearly dependent on dietary protein. By the same criterion, protein had no effect on the utilization of the lowest level of retinyl acetate supplementation. In contrast, utilization of larger amounts of retinyl acetate was diminished in protein deficiency, but was unaffected by excessive protein intake.