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Patterns of Protein Feeding and the Biosynthesis of Vitamin A from Carotene in Rats^1,2,

Food and Nutrition Department, Iowa State University, Ames, Iowa 50010

The effect of dietary protein level and the simultaneous presence of protein and carotene in the gastrointestinal tract on carotene utilization was investigated in young male rats depleted of hepatic and renal vitamin A. A spaced-feeding regimen was used to create two different digestive phases, characterized by the presence or absence of protein. Carotene utilization was evaluated by deposition of hepatic and renal vitamin A during a 28-day supplementation period and by formation of labeled products from ¹⁴C-ß-carotene on the day of autopsy. Vitamin A deposition was increased (58, 105, 147 µg) as protein constituted 10, 20, or 40% of the diet. ¹⁴C-retinyl ester recovery from the intestine was likewise increased (9.6, 12.2, and 15.5% of the injected dose, respectively) in these animals. Depending on the length of the metabolic period, ¹⁴C-retinyl ester formation in rats fed 20 or 40% protein was enhanced in those prefed protein-containing meals compared with protein-free meals. In vitro preparations from rats prefed protein rather than protein-free meals also converted more ¹⁴C-ß-carotene to labeled retinal.

KEY WORDS: • ß-carotene • retinol • dietary protein • meal pattern

¹ Journal Paper no. J-7355 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project 1895. This study was supported in part by a National Defense Education Act Title IV Fellowship.

² Part of this work was presented at the meeting of the Federation of American Societies for Experimental Biology, Chicago, Ill., April 1971. Federation Proc. 30: 584 (abstr.).

Manuscript received 16 October 1972.