EFFECTS OF DIET-INDUCED HYPERTHREONINEMIA .1. AMINO-ACID LEVELS IN THE CENTRAL-NERVOUS-SYSTEM AND PERIPHERAL-TISSUES

Rats were fed four levels of threonine (Thr, 0.4, 0.6, 0.8, and 5.8g/1 00 g diet). After two weeks, Thr, serine (Ser), and glycine (Gly) leve ls were measured in plasma, liver, muscle, and central nervous system. The diet containing 5.8 g/100 g of Thr elevated Thr and Gly concentra tions in plasma and nervous tissue in comparison with a standard diet. In muscle and liver, Thr concentrations were also raised but Gly leve ls did not change. The hepatic Thr dehydratase activity was enhanced. Diets containing moderate Thr quantities (0.6 and 0.8 g/100 g) induced slight elevations of Thr levels in all tissues. Gly concentrations we re not modified. The activity of hepatic Thr dehydratase was diminishe d. Our results show that a high dietary content of Thr (15 times the n ormal levels) elevates Gly levels in various tissues, including the br ain. On the contrary, diets containing 2 to 4 times the normal levels of Thr induce a weak hyperthreoninemia insufficient to modify brain Gl y.