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Effect of Alteration of the Light-Darkness Cycle on Amino Acid Utilization in the Adult Rat

Life Sciences Division, Technology Incorporated, Houston, Texas 77058, National Aeronautics and Space Administration, Manned Spacecraft Center, Houston, Texas 77058 and Department of Nutritional Sciences, The University of Wisconsin, Madison, Wisconsin 53706

Mature male Sprague-Dawley rats (225 to 400 g) were exposed to various lengths of light and darkness and fed diets containing 3, 4, 5, or 7% of an amino acid mixture. Experimental diets were consumed during a 7-day dietary adjustment period which was followed by a 10-day metabolic period. Samples of urine and feces were collected at 48-hour intervals. Blood samples were obtained at the end of the metabolic period. Experimental animals consuming a diet containing 7% of an amino acid mixture increased in body weight during the 10-day metabolic period. The length of the light-dark cycle adversely affected diet utilization, especially the 2/2-hour cycle. All measurements made — food, water, and nitrogen intakes; food/water intake ratios; hemoglobin content; liver, spleen, and adrenal weights; nitrogen retention and excretion, and serum protein and albumin/globulin — were significantly affected by the length of the light-dark cycle. Animals exposed to long or short light-dark cycles generally suffered adverse effects when compared with groups subjected to intermediate lighting cycles. The level of amino acid mixture in the diet did not affect food intake, food/water intake ratio, liver or spleen weights, liver nitrogen content serum protein, or albumin/globulin ratio. There were significant interactions between diet and light-dark cycle length on food intake, spleen weight, and retained and fecal nitrogen.

KEY WORDS: • light-darkness cycle • amino acid

Manuscript received 1 November 1971.