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

Abstract

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). 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. 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). 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.