Some Biochemical Changes in Hamsters Fed Excess Phenylalanine Diets. ∗

Abstract

Previous studies in this laboratory have revealed that feeding excess quantities of phenylalanine to rats influences the activity of various liver enzymes(1,2,3), the quantity of brain serotonin(2,4), plasma amino acid levels, and affects these parameters in the developing fetus(5,6). Behavioral responses of rats fed such diets have also been evaluated (7,8). Other studies by Waisman and Har-low(9,10) have provided convincing data that the Rhesus monkey is a better animal than the rat for both biochemical and behavioral experiments designed to study the effect of hyperphenylalaninemia.

In attempts to develop still other animal models of hyperaminoacidemias, hepatic phenylalanine hydroxylase activities of animals of several species were determined and it was surprising to find that the Syrian hamster (Cricetus auratus) had but 18% of the hydroxylase activity of the rat(11). The purpose of this study was to determine the effect of different phenylalanine-supplemented diets on growth, plasma phenylalanine and tyrosine levels, phenylalanine hydroxylase, phenylala-nine-pyruvate transaminase, and tyrosine-a-ketoglutarate transaminase activity in the liver of the growing hamster.

Materials and methods. Weanling hamsters, 25 days of age, were obtained from a local vendor (Con Olson Co., Madison, Wis.) and placed in individual cages, in a room with 3-hour alternate dark-light cycles as previously described(12). The animals were randomized in groups of six, 3 ♂and 3 ♀ to a group, and fed different diets. The first 5 groups received commercial diet,‡ supplemented with varying amounts of L-phenylala-nine, or L-phenylalanine + DL-phenylala-nine; a group which received only commercial diet served as controls. Eight other groups received synthetic diets consisting of varying quantities of casein and dextrose plus corn oil, minerals,§ and vitamins. This basic diet was supplemented with 5% L-phenylalanine or a mixture of L-phenylalanine and DL-phenylalanine, as listed in Table I.