Phosphate-activated glutaminase activity is enhanced in brain, intestine and kidneys of rats following portacaval anastomosis

AIM: To assess whether portacaval anastomosis (PCA) in rats affects the protein expression and/or activity of glutaminase in kidneys, intestines and in three brain areas of cortex, basal ganglia and cerebellum and to explain the neurological alterations found in hepatic encephalopathy (HE). METHODS: Sixteen male Wistar rats weighing 250-350 g were grouped into sham-operation control (n=8) or portacaval shunt (n=8). Twenty-eight days after the procedure, the animals were sacrificed. The duodenum, kidney and brain were removed, homogenised and mitochondria were isolated. Ammonia was measured in brain and blood. Phosphate-activated glutaminase (PAG) activity was determined by measuring ammonia production following incubation for one hour at 37 celsius degree with O-phthalaldehyde (OPA) and specific activity expressed in units per gram of protein (mukat/g of protein). Protein expression was measured by immunoblotting. RESULTS: Duodenal and kidney PAG activities together with protein content were significantly higher in PCA group than in control or sham-operated rats (duodenum PAG activity was 976.95+/-268.87 mukat/g of protein in PCA rats vs 429.19+/-126.92mukat/g of protein in sham-operated rats; kidneys PAG activity was 1259.18+/-228.79 mukat/g protein in PCA rats vs 669.67+/-400.8 mukat/g of protein in controls, P<0.05; duodenal protein content: 173% in PCA vs sham-operated rats; in kidneys the content of protein was 152% in PCA vs sham-operated rats). PAG activity and protein expression in PCA rats were higher in cortex and basal ganglia than those in sham-operated rats (cortex: 6646.6+/-1870.4 mukat/g of protein vs 3573.8+/-2037.4 mukat/g of protein in control rats, P<0.01; basal ganglia, PAG activity was 3657.3+/-1469.6 mukat/g of protein in PCA rats vs 2271.2+/-384 mukat/g of protein in sham operated rats, P<0.05; In the cerebellum, the PAG activity was 2471.6+/-701.4 mukat/g of protein vs 1452.9+/-567.8 mukat/g of protein in the PCA and sham rats, respectively, P<0.05; content of protein: cerebral cortex: 162%+/-40% vs 100%+/-26%, P<0.009; and basal ganglia: 140%+/-39% vs 100%+/-14%, P<0.05; but not in cerebellum: 100%+/-25% vs 100%+/-16%, P=ns). CONCLUSION: Increased PAG activity in kidney and duodenum could contribute significantly to the hyperammonaemia in PCA rats, animal model of encephalopathy. PAG is increased in non-synaptic mitochondria from the cortex and basal ganglia and could be implicated in the pathogenesis of hepatic encephalopathy. Therefore, PAG could be a possible target for the treatment of HE or liver dysfunction.