Indomethacin prevents the development of experimental ammonia-induced brain edema in rats after portacaval anastomosis

Patients with fulminant hepatic failure (FHF) die with brain edema, exhibiting an increased cerebral blood flow (CBF) at the time of cerebral swelling. Mild hypothermia prevents brain edema in experimental models and in humans with FHF, an effect associated with normalization of CBF. To study the effects of alterations of CBF on the development of brain edema, we administered intravenous (IV) indomethacin to rats receiving an ammonia infusion after portacaval anastomosis. This model predictably develops brain edema and a marked increase in CBF at 3 hours of infusion. Brain water was measured with the gravimetry technique; CBF was monitored with both laser Doppler flowmetry and radioactive microspheres, whereas intracranial pressure (ICP) was monitored with a cisterna magna catheter. Coadministration of indomethacin prevented the increase in CBF seen with ammonia alone (110 +/- 19% vs. -2 +/- 9%) as well as the increase in brain water (80.86 +/- 0.12% vs. 80.18 +/- 0.06%) and the increase in ICP. Plasma ammonia and brain glutamine levels were markedly elevated in the ammonia-infused group and unaffected by indomethacin. However, ammonia uptake by the brain was significantly reduced by indomethacin. Levels of 6-keto-PGF(1alpha), a stable metabolite of prostacyclin, were reduced in the cerebrospinal fluid (CSF) of indomethacin-treated animals. As with mild hypothermia, avoiding cerebral vasodilatation with indomethacin will prevent the development of brain edema in this hyperammonemic model. Cerebral vasoconstriction reduces cerebral ammonia uptake and, if selective to the brain, may be of benefit in FHF.     

Mild hypothermia modifies ammonia-induced brain edema in rats after portacaval anastomosis

BACKGROUND & AIMS: The pathogenesis of brain edema in fulminant hepatic failure is still unresolved. Mild hypothermia (33 degrees-35 degreesC) can ameliorate brain edema after traumatic brain injury. We evaluated mild hypothermia in a model of ammonia-induced brain edema in which accumulation of brain glutamine has been proposed as a key pathogenic factor. METHODS: After portacaval anastomosis, anesthetized rats were infused with ammonium acetate at 33 degrees, 35 degrees, and 37 degreesC or vehicle at 37 degreesC. Water and glutamine levels in the brain, cardiac output, and regional and cerebral hemodynamics were measured when intracranial pressure increased 3-4-fold (ammonia infusion at 37 degrees) and matched times (other groups). RESULTS: Mild hypothermia reduced ammonia-induced brain swelling and increased intracranial pressure. Brain glutamine level was not decreased by hypothermia. Brain edema was accompanied by a specific increase in cerebral blood flow and oxygen consumption, which were normal in both hypothermic groups. When the ammonia infusion was continued in hypothermic rats, plasma ammonia levels continued to increase and brain swelling eventually developed. CONCLUSIONS: Mild hypothermia delays ammonia-induced brain edema. In this model, an increase in cerebral perfusion is required for brain edema to become manifest. Mild hypothermia could be tested for treatment of intracranial hypertension in fulminant hepatic failure.     

Cerebral hyperemia and nitric oxide synthase in rats with ammonia-induced brain edema

BACKGROUND/AIM: Brain edema is a common fatal complication in acute liver failure. It is related to an acute change in brain osmolarity secondary to the glial accumulation of glutamine. Since high cerebral blood flow (CBF) precedes cerebral herniation in fulminant hepatic failure we first determined if an increase in brain water and glutamine are prerequisite to a rise in CBF in a model of ammonia-induced brain edema. Secondly, we determined if such a cerebral hyperperfusion is mediated by nitric oxide synthase (NOS). METHODS: Male rats received an end-to-side portacaval anastomosis (PCA). At 24 h, they were anesthetized with ketamine and infused with ammonium acetate (55 microM/kg per min). Studies were performed at 60, 90, 120, 150 and 180 min after starting the ammonia infusion and once the intracranial pressure had risen three-fold (mean 210'). Brain water (BW) was measured using the gravimetry method and CBF with the radioactive microsphere technique. Glutamine (GLN) in the CSF was sampled via a cisterna magna catheter. The neuronal NOS was specifically inhibited by 1-2-trifluoromethylphenyl imidazole (TRIM, 50 mg/kg intraperitoneally) and in separate studies nonspecifically by N-omega-nitro-L-arginine (L-NNA, 2 microg/kg per min intravenously) RESULTS: At 90', brain water was significantly increased (P < 0.015) as compared to the 60' group while CBF was significantly different at 150'. A significant correlation was observed between values of CBF and brain water (r = 0.88, n = 36, P < 0.001). Administration of either TRIM or L-NNA did not prevent the development of cerebral hyperperfu. sion and edema. CONCLUSION: We observed that cerebral hyperemia follows an initial rise in brain water content, rather than in the cerebrospinal fluid concentration of glutamine. The rise in CBF further correlated with brain water accumulation and was of critical importance for the development of intracranial hypertension. The unique mechanism for the rise in CBF in hyperammonemia was not prevented by NOS inhibition indicating that NO is not the mediator of high CBF and intracranial hypertension.     

Cerebral blood flow and metabolism in hepatic cirrhosis before and after portacaval shunt operation

It has been demonstrated that cardiac output and pulmonary, gastroduodenal, pancreatic, and splenic blood flow increases after portacaval shunt operations. This report concerns a study of cerebral haemodynamics and metabolism in eight patients with cirrhosis of the liver, examined both before and after portacaval surgical anastomosis. The patients were fully alert and orientated to mental and neurological examination at all times.In each subject the cerebral blood flow, cerebral vascular resistance, cerebral metabolic rate of oxygen and of glucose, and glucose/oxygen quotient were determined.This investigation showed that a portacaval shunt operation is followed by a significant increase in the cerebral blood flow and a significant decrease in the cerebral vascular resistances. No important variation in the cerebral metabolic rate of oxygen was observed, but both the cerebral metabolic rate of glucose and the glucose: oxygen quotient showed significant increases.The presence of toxic substances which, shunting the liver, enter the general circulation could be the cause of the increased cerebral blood flow, while the increase in the cerebral metabolic rate of glucose could result from a greater cerebral detoxication, for example, the cerebral synthesis of glutamine.     

Cerebral blood flow autoregulation and edema formation during pregnancy in anesthetized rats

Eclampsia is considered a form of hypertensive encephalopathy in which an acute elevation in blood pressure causes autoregulatory breakthrough, blood-brain barrier disruption, and edema formation. We hypothesized that pregnancy predisposes the brain to eclampsia by lowering the pressure of autoregulatory breakthrough and enhancing cerebral edema formation. Because NO production is increased in pregnancy, we also investigated the role of NO in modulating autoregulation. Cerebral blood flow autoregulation was determined by phenylephrine infusion and laser Doppler flowmetry. Four groups were studied: untreated nonpregnant (n=7) and late-pregnant (days 19 to 21; n=8) Sprague-Dawley rats and nonpregnant (n=8) and late-pregnant (n=8) animals treated with an NO synthase inhibitor (N(G)-nitro-l-arginine methyl ester; 0.5 to 0.7 g/L). Brain water content and blood-brain barrier permeability to sodium fluorescein were determined after breakthrough. Pregnancy caused no change in autoregulation or the pressure of breakthrough. However, treatment with the NO synthase inhibitor significantly increased the pressure of autoregulatory breakthrough (nonpregnant: 183.6+/-3.0 mm Hg versus 212.0+/-2.8 mm Hg, P<0.05; late-pregnant: 180.8+/-3.2 mm Hg versus 209.3+/-4.7 mm Hg, P<0.05). After autoregulatory breakthrough, only late-pregnant animals showed a significant increase in cerebral edema formation, which was attenuated by NO synthase inhibition. There was no difference in blood-brain barrier permeability between nonpregnant and late-pregnant animals in response to acute hypertension, suggesting that pregnancy may predispose the brain to eclampsia by increasing cerebral edema through increased hydraulic conductivity.     

Hyperplastic foci in the atrophic liver of rats after portacaval anastomosis

Hyperplastic focal areas were investigated in livers of male rats 1 and 9 months after portacaval anastomosis (PCA) by light and electron microscopy. These alterations, predominantly found in periportal areas, were characterized by light microscopy as clusters of enlarged hepatocytes along narrowed sinusoids, contrasting in the remaining liver acinus with smaller hepatocytes along widened sinusoids. No differences were observed between 1 and 9 months PCA except for glycogen content, which was homogeneously distributed in the liver at 1 month but completely lacking in foci at 9 months. The most striking ultrastructural alterations were the sinusoids delimited in these hyperplastic areas by a thickened barrier consisting of thick endothelial cells encircled by numerous subendothelial processes of the perisinusoidal fat-storing cells. Deep and widened recesses of the sinusoidal lumen separated the two-cell-thick plates of the hyperplastic cells. Hepatocytes in foci, thought to represent regenerative areas, tend to increase their exchange surface. Their progressive loss in glycogen and their two-cell-thick plates architecture should be in favour of a potential malignancy. However, the spontaneous evolution of these foci which do not necessarily give rise to nodules, as well as the lack of other features of transformation, do not support this possibility.     

丁基苯酞对重型弥漫性脑创伤大鼠脑血流量及脑水肿的影响

目的 观察丁基苯酞对脑创伤后大鼠脑血流量及脑水肿的影响.方法 191只成年雄性Sprague-Dawlley大鼠,体重(330 ±20)g,随机(随机数字法)分为对照组(40只)、模型组(57只)、低剂量丁基苯酞干预组(57只,剂量80 mg/kg),高剂量丁基苯酞干预组(剂量120 mg/kg).各组分别在伤后3、6、24、48、72 h每组取4只大鼠应用激光多普勒血流计观察脑组织血流量变化;伊文思蓝法标记微血管通透性;干湿法测定脑组织含水量.采用SPSS 17.0对实验数据进行统计分析,正常对照组与模型组脑血流量、脑组织水含量、伊文思蓝透过量和含量比较采用析因设计资料的方差分析,组内分析采用SNK-q分析,P＜0.05为差异有统计学意义.结果 与模型组比较,丁基苯酞干预组中,6、24、48、72 h脑血流血量增加(q=23.37 ～ 26.10,P＜0.05);伊文思蓝含量降低(q=3.53～25.55,P＜0.05);脑组织含水量降低(q=23.37 ～ 26.10,P＜0.05);高剂量丁基苯酞干预组上述指标变化在更为显著(q =6.59 ～8.96,7.52 ～8.53,7.89～ 20.78,P＜0.05).结论 丁基苯酞增加脑创伤后大鼠脑血流量,减轻血管通透性和脑水肿,对重型脑创伤有保护作用.     

Sex hormones and fertility following portacaval anastomosis in rats

Portocaval anastomosis (PCA) in the normal male rat causes profound alterations in testicular morphology and function and in plasma levels of sex steroids as well as of gonadotropins. Testicular atrophy is accompanied by a significant decrease of plasma testosterone (0.03 ng/ml versus 0.99 ng/ml) and an increase of estradiol (76.2 pg/ml versus 39.7 pg/ml) and estrone (68. pg/ml versus 45.5 pg/ml). Plasma levels of gonadotropins (LH, FSH) and prolactin are lowered too (LH: 15 ng/ml versus 28.5 ng/ml, FSH:119 versus 182 ng/ml, prolactin:53 versus 109 ng/ml). The altered sex hormone metabolism is reflected in marked changes of the morphology and nucleic acid content of the metabolizing organs i.e. liver, gonades and kidney. The results of this study are consistent with the hypothesis that portosystemic shunt per se plays an important role in the pathogenesis of the disturbed metabolism of sex hormones observed in patients with liver cirrhosis and portal hypertension.     

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 en-cephalopathy (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℃with O-phthalaldehyde (OPA) and specific activity expressed in units per gram of protein (μkat/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±268.87μkat/g of protein in PCA rats vs 429.19±126.92.μkat/g of protein in sham-operated rats; kidneys PAG activity was 1259.18±228.79μkat/g protein in PCA rats vs 669.67±400.8μkat/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±1870.4μkat/g of protein vs 3573.8±2037.4μkat/g of protein in control rats, P<0.01; basal ganglia, PAG activity was 3657.3±1469.6μkat/g of protein in PCA rats vs 2271.2±384μkat/g of protein in sham operated rats, P<0.05; In the cerebellum, the PAG activity was 2471.6±701.4μkat/g of protein vs 1452.9±567.8μkat/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 hyperam-monaemia 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.     

Cerebral glucose utilization and blood flow in adult spontaneously hypertensive rats.

Not only blood pressure but also behavioral activity, brain morphology, and cerebral ventricular size differ between young spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. This suggests that cerebral blood flow and cerebral metabolism may vary between these two rat strains. To test this hypothesis, we measured local cerebral glucose utilization in 31 brain areas of 26-30-week-old rats. Local cerebral blood flow was also assessed in these same areas. Cerebral glucose utilization was measured by the 2-deoxyglucose method; cerebral blood flow was determined by the iodoantipyrene method. In virtually all gray matter structures, the apparent rate of glucose utilization was lower in SHR than in normotensive WKY rats; the interstrain differences varied significantly among structures and were statistically significant (uncorrected t tests) in 14 of 28 gray matter areas. Local cerebral blood flow was fairly similar in the two rat strains. The coupling of blood flow to glucose utilization varied significantly among brain areas in normotensive WKY rats as well as in SHR. In a number of gray matter structures, the coupling of flow to metabolism differed between hypertensive and normotensive animals. These data suggest that for many brain areas, either glucose utilization or glucose partitioning differs between WKY rats and SHR.     

Marion's calibrated latero-lateral portacaval anastomosis: a truncular shunt maintaining hepatopetal portal blood flow?

The authors report the hemodynamic study of 22 cases of calibrated side-to-side portacaval shunts performed in patients with liver cirrhosis. In all patients, hepatopetal portal blood flow was present before the operation. According to the data obtained by scintiangiography and angiography, hepatopetal portal flow was maintained in 70 p. 100 of the patients immediately after the operation. After one year there was a discrepancy between the results of scintiangiography and those of conventional angiography: while portal flow seemed to be hepatopetal on the scintigraphy in 11 of controlled patients, it decreased or disappeared on the angiography in 6 other controlled patients. These results are comparable to those of selective shunts and suggest that the calibrated side-to-side portacaval shunt is a valuable procedure in maintaining hepatopetal portal flow. A controlled trial would be useful to assess the place of this operation in the treatment of portal hypertension due to cirrhosis.     

Lipoprotein catabolism in rats with portacaval anastomosis on various diets

The catabolism of lipoproteins was measured in rats with a portacaval anastomosis and in intact control rats. Radioiodinated rat high density lipoproteins or human low density lipoproteins, the major cholesterol-bearing lipoproteins in rat or man respectively, were injected intravenously into rats. More than 90% of trace amounts of these lipoproteins were removed from plasma of rats with portacaval anastomosis and controls on standard chow at closely similar rates within 24 h. Also, [125I]high density lipoproteins left the plasma at comparable rates in controls and rats with portacaval anastomosis, whether fed with a cholesterol-free chow or a carbohydrate-rich lard chow. These dietary regimens were employed to avoid artifacts through a different development of the body weight in operated and control rats. A standard laboratory chow ad libitum led to weight loss in rats with portacaval anastomosis. Pair-fed with a cholesterol-free chow both groups of rats kept the same weight, but only with a carbohydrate-rich lard chow could the natural weight gain be achieved. In all rats with portacaval anastomosis liver weights were reduced and serum cholesterol decreased by 21-31% with the major change in high density lipoproteins. The findings suggest that cholesterol concentrations are not likely to be lowered in rats with portacaval anastomosis by enhanced lipoprotein catabolism.     

Effect of portacaval or mesentericocaval anastomosis on cholesterol metabolism in rats

Portacaval anastomosis (PCA) lowered by 50% the cholesterol concentration in the plasma of rats. The free and esterified cholesterol contents in the lipoproteins were decreased with the very low density lipoproteins most affected (-85%). Cholesterol concentration as total content in the liver was reduced. The major change in the cholesterol metabolism, as studied with an isotopic equilibrium method, was the decrease in the intestinal absorption coefficient of dietary cholesterol (56.0 +/- 2.7% instead of 73.3 +/- 1.9% in controls). The rate of cholesterol transformation into bile acids was decreased (10.5 +/- 0.3 vs 14.5 +/- 0.5 mg/day/rat in controls). The rate of internal secretion of cholesterol was slightly reduced while the rate of fecal external secretion was increased, suggesting that the synthesis of cholesterol by extra-digestive tissues (including liver) was reduced after PCA. The effects of PCA on cholesterol metabolism were similar to those described for glucagon administration. Since this shunt results in hyperglucagonemia, it is suggested that this hormonal perturbation was the main factor involved in the modifications of cholesterol metabolism after PCA. Moreover, mesentericocaval anastomosis, which shunts only the intestinal blood and allows the pancreatic hormones a normal transport through the liver, did not significantly modify cholesterol metabolism. Only cholesterolemia (-28%) and the absorption coefficient of dietary cholesterol (66.0 +/- 2.3%) were slightly reduced.     

Regional blood-brain barrier transport of glucose after portacaval anastomosis

The regional influx of glucose across the blood-brain barrier was measured in rats 5 to 6 weeks after a portacaval anastomosis or sham operation. D-[¹⁴C]Glucose was infused intravenously for 15sec while arterial blood was sampled continuously for measurement of plasma radioactivity and glucose concentration. Brain tissue radioactivity was measured by quantitative autoradiography. Glucose influx and plasma clearance (permeability times surface area;PS) were calculated from the net disintegrations per minute per gram in brain, the plasma radioactivity integral, and the plasma glucose concentration. In shunted rats influx was decreased by about 22% (in the brain as a whole) compared to that in controls. This decrease was almost entirely due to the decrease in plasma glucose concentrations (27%). ThePS, normalized to take plasma concentrations into account, showed a slight decrease in most of the brain except the telencephalon. For the brain as a whole this decrease amounted to 11%. The regionalPS and glucose utilization are known to be coupled and the relationship between these was the same in sham-operated and shunted rats. The decrease inPS observed in shunted rats was commensurate with their lower rates of glucose use; thus, the transport process of glucose from plasma to brain appeared to be unaffected by portacaval shunting.