Rat cerebral mitochondrial glutaminase activity is unaffected by moderate hyperammonemia in two models.

The phosphate-dependent (PAG) and phosphate-independent (PIndG) glutaminase activities were measured in cerebral perikaryal mitochondria derived from rats subjected to ammonium acetate- induced "simple" hyperammonemia (SHA) or thioacetamide-induced hepatic encephalopathy (HE). These two moderately hyperammonemic conditions were previously found to be accompanied by pronounced changes in virtually all the enzyme activities coupling the tricarboxylic acid cycle to the synthesis and metabolism of the excitatory neurotransmitter glutamate. Both PAG and PIndG remained unaffected by SHA or HE, indicating that they do not contribute to the cerebral glutamine/glutamate imbalance associated with both conditions.