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Effect of Alteration of the Light-Darkness Cycle on Lactalbumin 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 were exposed to various lengths of light and darkness and were fed diets containing 3, 4, 5 and 7% lactalbumin. 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 and blood samples at the end of the metabolic phase. Only the rats consuming the 7% lactalbumin diet increased in body weight during the 10-day metabolic period. The length of the light-dark cycle adversely affected diet utilization, especially at the lower lactalbumin levels. Significant differences in food, water and nitrogen intake, food/water intake ratio, hemoglobin concentration, mean corpuscular hemoglobin concentration, fecal and urinary nitrogen loss, and liver, spleen and adrenal gland weights, liver nitrogen content, and retention of ingested nitrogen of adult rats were induced by changes in the length of the light-dark cycle. In general, animals exposed to 2/2, 4/4 or 18/18-hour light-dark cycles suffered adverse effects when compared to groups subjected to the other lighting regimens. Differences attributable to lactalbumin levels in the diet were not detected in any parameter previously denoted except for nitrogen intake, liver and adrenal gland weight, serum protein concentration, albumin/globulin ratio, mean corpuscular hemoglobin and fecal and urinary nitrogen. A significant (P < 0.01) interaction between diet and length of the light-dark cycle was found for liver weight per unit body weight.

KEY WORDS: • light-darkness cycle • lactalbumin

Manuscript received 1 November 1971.