J. ment. Dejic. lies. (1977) 21, 95 95 FREE AMINO ACIDS IN THE TISSUES OF RATS WITH EXPERIMENTALLY INDUCED PHENYLKETONURIA F. VALDIVIESO, MAGDALENA UGARTE, M. MATIES, C. GIMENEZ and F. MAYOR Departamento de Bioquimicay Biologia Molecular, Centro de Biologfa Molecular, Universidad Autonoma de Madrid, Cantoblanco, Madrid-34, Spain The inborn error phenylketonuria (PKU) is caused by a deficiency of liver phenylalanine 4-hydroxylasc (EC 1.14.16.1), and leads to a marked accumulation ofphenylalanine in lhe blood and tissues of phenylketonuric patients (Jervis, 1953). In spite of the number of studies on the pathogenesis of phenylketonuria (for a review see Gaull, Tallan, Lajtha and Rassin, 1975), the aetiology of the mental retardation accompanying this inherited enzymatic defect, that is, how the increased phenylalanine concentration results in the brain dysfunction, remains uncertain. The transport of any particular amino acid into the brain depends not only on its own concentration but also on the concentrations of other amino acids in the blood (Pratt, 1976). Thus, raised blood levels ofphenylalanine in PKU would lead to the exclusion of amino acids from the brain by inhibition of transport mechanisms (Daniel, Moorhouse and Pratt, 1976) and hence reduction of the rate of protein synthesis since this process probably depends on free amino acid concentrations in the brain (Roberts and Morelos, 1965). Prensky, Carr and Moser (1968) and Menkes (1968) observed decrea.sed amounts of myelin protein in the brain of untreated phenylketonurics. Further, Agrawal, Bone and Davison (1970) suggested that impaired myelination in phenylketonuria may be due to a decrease of the free amino acid pool in the developing brain. We have previously shown (Valdivieso, Gimenez and Mayor, 1975) that the tise of p-chiorophenylalanine (p-GPA), an inhibitor ofphenylalanine 4-bydroxylase in vivo, and esculin, a pteridine antagonist which reinforces lhe inhibition produced by p-GPA, supplies an improved experimental model of PKU useful for biochemical studies (CJimencz, Valdivieso and Mayor, 1974). The present paper reports the changes in the concentrations ofphenylalanine and tyrosine in the liver, blood and brain of rats with experimentally induced phenylketonuria. 'i'lie effects of high concentrations of phenylalanine on the amino acid concentrations in lhe blood, liver and brain of phenylketonuric rats are also reported. MEIHODS Adult rats of the Wistar strain weighing 150-200 g were used. Animals had free access to food and water during the experiments. Experimental phenylketonuria was induced as described (Gimenez et al., 1974) by intrapcritoneal injections of DL-p-chlorophenylalanine (p-CPA, 360 mg/kg), esculin hydrate (680 mg/kg) and L-phenylalanine (1 g/kg) thirty-six hours, one hour and one hour respectively, before killing. Litter-mate controls received also intraperitoneal doses of 0.9o;, NaCl instead of p-GPA, esculin and phenylalanine. Animals were sacrificed by decapitation. Received 11th .N'ovember, 1976