Influence of an Aromatic Amino Acid Decarboxylase Inhibitor on GTP Cyclohydrolase I Activity in the Rat Brain

Abstract

Based on the hypothesis that catecholamine decreases may cause increases in biopterin, we measured the GTP cyclohydrolase I(GTPCH-I) activity and biopterin content in the cerebral cortex, midbrain/diencephalon, cerebeilum, pons/medulla oblongata, striatum , and hippocampus of brains from rats given NSDlOIS, an inhibitor for aromatic amino acid decarboxylase . The catecholamine contents decreased in all the regions tested. The changes in the GTPCH -I activity and bioptcrin content were different among the regions; they decreased in some regions contrary to expectations and increased in other regions. However, either the enzyme activity or biopterin content increased in the midbrain/ diencephalon and pons/ medulla oblongata, in which similar levels of catecholamines, GTPCH -I activity and biopterin were detected. These results suggest that for the midbrain/diencephalon and pons/medulla oblongata the surmise that a decrease in catecholamines causes an increase in the biopterin synthesis may be correct.

Keywords

• gtp cyclohydrolase i (ec 3.4.s.16)
• aromatic l-amino acid decarboxylase (ec 4.1.1.28)