Self-Selection of Phenylalanine in the Rat

Abstract

The regulation of phenylalanine intake in rats was investigated by means of a self-selection feeding method. The relationship between phenylalanine intake and the alteration of phenylalanine and tyrosine concentrations in plasma and brain was also studied. Weanling rats were offered a choice of two diets differing only in phenylalanine content for 2 weeks. Weight gain and food consumption of all the selfselecting rats were not significantly different from each other and were of the same levels as those in rats fed on a 10% casein or 10% casein plus 1.0% phenylalanine diet as a fixed ratio. Phenylalanine intake of the selfselecting rats ranged from 0.31 to 2.29% of the food consumed. The phenylalanine and tyrosine concentrations in plasma and brain of selfselecting rats were within normal levels. It became clear that rats have an ability to regulate phenylalanine intake, and that they select phenylalanine to meet their requirement for the amino acid.