BLOOD AMINO ACID STUDIES: III. EFFECTS OF AMOUNT AND QUALITY OF DIETARY PROTEIN AND LENGTH OF TEST PERIOD ON PLASMA FREE LYSINE LEVELS IN THE RAT

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Abstract
Male rats were given diets containing 10 or 20% protein from fish flour or wheat gluten plus histidine, methionine, threonine, and tryptophan, and plasma free lysine levels were determined after 3 and 7 days. The levels dropped by approximately 50% from initial values when the diet contained gluten and rose by approximately 100% when the diet contained fish flour. The protein level of the diet had no significant effect on plasma free lysine levels. Values found after 3 days were similar to those found after 7 days.In further studies, male rats were fasted for 19 hours and given diets containing 10% protein from bread or fish flour for 2 hours, 1 day, or 3 days. No marked effects of diet on plasma free lysine values were found after 2 hours, but after 1 or 3 days values found with bread were much lower than those with fish flour. Plasma free lysine levels of animals given heat-damaged casein or soy flour were lower than those of animals given unheated proteins. It was concluded that plamsa free lysine levels reflect the amount and availability of lysine in the food.