Na+, K+-ATPase activity was measured in synaptic plasma membrane from cerebral cortex of Wistar rats subjected to experimental phenylketonuria, i.e., chemical hyperphenylalaninemia induced by subcutaneous administration of 5.2 micromol phenylalanine / g body weight (twice a day) plus 0.9 micromol p-chlorophenylalanine / g body weight (once a day). The treatment was performed from the 6th to the 14th postpartum day and rats were killed 12 h after the last injection. Synaptic plasma membrane from cerebral cortex was prepared by a discontinuous density sucrose gradient for Na+, K+-ATPase activity determination. The results showed that the enzyme activity was decreased by 30% in animals subjected to experimental phenylketonuria when compared to control. The in vitro effects of the drugs on Na+, K+-ATPase activity were also investigated. Phenylalanine and p-chlorophenylalanine inhibited the enzyme activity and this inhibition was reversed by alanine. In addition, competition between phenylalanine and p-chlorophenylalanine for binding to the enzyme was observed, suggesting a common binding site for these substances. Our results suggest that reduction of Na+, K+-ATPase activity may be one of the mechanisms related to the brain dysfunction observed in human PKU.

Our objective was to investigate the effect of alanine administration on Na+,K+-ATPase activity in cerebral cortex of rats subjected to chemically-induced phenylketonuria. Wistar rats were treated from the 6th to the 28th day of life with subcutaneous injections of either 2.6 micromol alanine or 5.2 micromol phenylalanine plus 2.6 micromol alpha-methylphenylalanine per g body weight or phenylalanine plus alpha-methylphenylalanine plus alanine in the same doses or equivalent volumes of 0.15 M saline. The animals were killed on the 29th or 60th day of life. Synaptic plasma membrane from cerebral cortex was prepared for Na+,K+-ATPase activity determination. The results showed that alanine injection prevents the decrease of Na+,K+-ATPase activity in animals subjected to experimental phenylketonuria. Therefore, in case the same effects are achieved with ingested alanine, it is possible that alanine supplementation may be an important dietary adjuvant for phenylketonuric patients.