A role of nitric oxide as an inhibitor of gamma-aminobutyric acid transaminase in rat brain.

The present study has been aimed to investigate the effect of nitric oxide (NO) on the concentration of gamma-aminobutyric acid (GABA) in rat brain. The concentrations of GABA and glutamate and the activities of glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid transaminase (GABA-T) were determined in groups of animals 5 and 30 min after intraperitoneal injection of a NO-increasing dose (1,000 mg/kg) of its precursor, L-arginine and a dose (50 mg/kg) of N-nitro-L-arginine methyl ester (L-NAME) that inhibits NO synthesis from L-arginine. L-arginine-induced elevation of NO concentration was accompanied by an increased concentration of GABA in the brain. GABA-T activity was inhibited in these animals. NO-decreasing action of L-NAME coincided with a reduction in the concentration of GABA and an enhancement of GABA-T activity. Both L-arginine and L-NAME did not alter the activity of GAD and the concentration of glutamate. An interpretation of these data suggests that NO has a GABA-T-inhibiting role in the brain.