Effect of lipopolysaccharide on in vivo and genetic regulation of rat urea synthesis.

BACKGROUND: The acute phase response causes a negative nitrogen balance. It is unknown whether this involves regulation of hepatic urea synthesis. METHODS: We examined the in vivo capacity of urea nitrogen synthesis (CUNS), mRNA levels of urea cycle enzyme genes and galactose elimination capacity (GEC) during moderate and severe acute phase response induced by low- and high-dose lipopolysaccharide (LPS) in rats. RESULTS: Low-dose LPS doubled CUNS (P<0.05), decreased the mRNA level of the rate-limiting urea cycle enzyme (arginino succinate synthetase (ASS) by 26% (P<0.05) and did not change GEC. High-dose LPS did not change CUNS, decreased the mRNA level of the flux-generating enzyme carbamoyl phosphate synthetase (CPS) by 11% (P<0.05) and the rate-limiting urea cycle enzyme (ASS) by 27% (P<0.05) and almost halved GEC (P<0.05). CONCLUSION: The moderate acute phase response up-regulated in vivo urea synthesis but had the opposite effect on gene level. The severe acute phase response decreased the functional liver mass that attenuated the increase in urea synthesis.     

CCl4 cirrhosis in rats: irreversible histological changes and differentiated functional impairment

Cirrhosis of the rat liver was induced by a 12 week individualized CCl4/phenobarbital treatment. After treatment, all surviving animals (81%) showed cirrhosis of the liver. The cirrhosis induced was irreversible when evaluated 24 weeks after cessation of treatment. Quantitative liver function measurements were reduced in a differentiated manner. Ranked according to the most pronounced changes they are: capacity of urea-N synthesis (CUNS), galactose elimination capacity (GEC) and antipyrine clearance (APC). Hepatic glutathione concentrations were only slightly decreased after the CCl4 treatment. It is possible to produce a high incidence of irreversible cirrhosis with differentiated functional impairment in the rat.     

The capacity of urea-N synthesis as a quantitative measure of the liver mass in rats

The capacity of urea-N synthesis (CUNS), the galactose elimination capacity (GEC) and the antipyrine clearance (APC) were measured in rats immediately after 30, 70 and 90% partial hepatectomy and after sham operation. CUNS was assessed during alanine infusion as urea accumulation in total body water, corrected for intestinal hydrolysis, and GEC was measured during constant galactose infusion in the same animals. APC was determined by the one-sample method in a separate group of animals, treated similarily. CUNS, GEC and APC were all correlated to the liver weight with correlation coefficients (r) above 0.8 and the correlation coefficients (r) between CUNS, GEC and APC were all above 0.7. It is concluded that CUNS is a quantitative measure of the functional liver mass in the rat.     

Growth hormone and insulin-like growth factor-I counteracts established steroid catabolism in rats by effects on hepatic amino-N degradation

Background/Aims: Long-term steroid treatment causes protein wasting. Liver contributes towards this by upregulating ureagenesis. Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are anabolic agents with specific hepatic effects. It is unknown whether IGF-I alone and/or in combination with GH have any effect on established hepatic amino-N catabolism during long-term glucocorticoid treatment.Methods: We measured the spontaneous (UNSR) and the substrate standardized rate of urea nitrogen synthesis (STUNSR), N-balance and mRNA levels of urea cycle enzymes in controls (placebo) and four longterm steroid treated groups given (1) prednisolone 4 mg/kg/day during 28 days (St) (2) +GH 1 mg/kg/day from day 21-28 (StGH) (3) +IGF-I 1.5 mg/kg/day 21-28 (StIGF) (4) GH +IGF-I (StGHIGF).Results: Steroid induced weight loss was stepwisely reversed by IGF-I, GH and both. UNSR, STUNSR and mRNA levels of urea cycle enzymes in the liver increased markedly after steroid treatment, and was normalized after co-administration of GH and IGF-I. N-balance improved after GH and IGF-I administration.Conclusions: Our results expands the knowledge of beneficial effects of GH on short-term steroid catabolism to include effects of IGF-I and IGF-I combined with GH on long-term steroid catabolism. Both peptides prevent steroid induced hepatic protein wasting and thereby contribute towards whole body anabolism. The effect in vivo is probably due to an effect of the peptides on urea cycle enzyme mRNA.     

Superoxide anion generating capacity and lysosomal enzyme activities of Kupffer cells in galactosamine induced hepatitis

To elucidate the function of the reticuloendothelial system of liver in hepatic injury, we investigated the effect of endotoxins on superoxide anion (O-2) generating capacity and lysosomal enzyme activities of Kupffer cells isolated from rats treated with galactosamine (Gal N), with Gal N supplemented with polymyxin B (Polymyxin B-Gal N), with lipopolysaccharide (LPS) and from control rats. After collagenase digestion of the liver and centrifugation over metrizamide gradient, Kupffer cells were prepared by the dish adherence procedure. O-2 production by the cells was examined as chemiluminescence during phagocytosis of latex particles and beta-glucuronidase activities were analyzed. High titers of endotoxemia were detected in LPS and Gal N rats by limulus test, while a low endotoxemia titer was found in Polymyxin B-Gal N rats. Hepatocyte damage was found in Gal N rats, but little was recognized in LPS and Polymyxin B-Gal N rats. In the latter groups, Kupffer cells, activated by endotoxins, showed the enhancement of chemiluminescence and a release of lysosomal enzyme. Though lysosomal enzyme was released from Kupffer cells in Gal N rats, chemiluminescence was slightly suppressed in spite of the high titer of endotoxemia. These results appear to be related to the consumption of O-2 during liver injury. The functional state of Kupffer cells was thus changed by the grade of endotoxemia and hepatic injury.     

Lysinuric protein intolerance presenting deficiency of argininosuccinate synthetase.

A 35-yr-old woman, who suffered from relapsing coma with hyperammonemia for 17 yr, was diagnosed to have lysinuric protein intolerance (LPI). Increased urinary dibasic amino acids (lysine, arginine and ornithine) and impaired absorption of orally administered lysine and arginine proved the defects of renal tubular and intestinal transport of dibasic amino acids. These defects are the primary cause of impaired urea cycle metabolism in LPI. Further, the level of argininosuccinate synthetase (ASS), a urea cycle enzyme, was analyzed and it was found to be below the normal level. This is the second reported case of LPI presenting ASS deficiency.     

Superoxide anion generating capacity of polymorphonuclear cells in patients with liver cirrhosis

The superoxide anion generating capacity of polymorphonuclear cells (PMNs) in patients with liver cirrhosis and the effect of lipopolysaccharide on rat PMNs were examined. Superoxide anion generating capacity of PMNs was measured as luminol-dependent photon emission (chemiluminescence) during phagocytosis of peptide in vitro. Chemiluminescence of PMNs from patients with liver cirrhosis was significantly enhanced compared with normal healthy volunteers, and endotoxemia was detected in 3 out of 20 cases of liver cirrhosis by the limulus gelatin test. Serial studies revealed that chemiluminescence of PMNs and endotoxin in plasma decreased after administration of polymyxin B (3 X 10(6) u/day). Chemiluminescence of rat PMNs was also markedly enhanced after the injection of lipopolysaccharide, and persisted for more than 8 days even though endotoxemia was not detected. These results indicate that the enhancement of chemiluminescence by PMNs is related to endotoxins spilling over from the liver in patients with liver cirrhosis.     

Rifaximin, but not growth factor 1, reduces brain edema in cirrhotic rats

AIM: To compare rifaximin and insulin-like growth factor (IGF)-1 treatment of hyperammonemia and brain edema in cirrhotic rats with portal occlusion.METHODS: Rats with CCl₄-induced cirrhosis with ascites plus portal vein occlusion and controls were randomized into six groups: Cirrhosis; Cirrhosis + IGF-1; Cirrhosis + rifaximin; Controls; Controls + IGF-1; and Controls + rifaximin. An oral glutamine-challenge test was performed, and plasma and cerebral ammonia, glucose, bilirubin, transaminases, endotoxemia, brain water content and ileocecal cultures were measured and liver histology was assessed.RESULTS: Rifaximin treatment significantly reduced bacterial overgrowth and endotoxemia compared with cirrhosis groups, and improved some liver function parameters (bilirubin, alanine aminotransferase and aspartate aminotransferase). These effects were associated with a significant reduction in cerebral water content. Blood and cerebral ammonia levels, and area-under-the-curve values for oral glutamine-challenge tests were similar in rifaximin-treated cirrhotic rats and control group animals. By contrast, IGF-1 administration failed to improve most alterations observed in cirrhosis.CONCLUSION: By reducing gut bacterial overgrowth, only rifaximin was capable of normalizing plasma and brain ammonia and thereby abolishing low-grade brain edema, alterations associated with hepatic encephalopathy.     

Effects of budesonide and prednisolone on hepatic kinetics for urea synthesis

BACKGROUND/AIMS: Glucocorticoids upregulate hepatic urea synthesis and cause protein breakdown to prevail over synthesis, releasing amino acids into the blood stream and increasing the substrate supply for hepatic urea synthesis. Budesonide is a new generation glucocorticoid that may be used for treatment of inflammatory diseases, e.g. Crohn's disease and autoimmune hepatitis. Due to its extensive first-pass metabolism in the liver, it has a potential adverse effect profile superior to that of prednisolone. Little attention has been directed towards differences in nitrogen catabolic properties between budesonide and prednisolone. METHODS: Eight normal male subjects (age 20-44 years; BMI 21.6-28.2 kg/m2) were randomly studied 3 times: 1) At baseline, 2) after 6 days of prednisolone (50 mg/day), and 3) after 6 days of budesonide (9 mg/ day). We measured urea nitrogen synthesis rates (UNSR) and blood alpha-amino-nitrogen (N) levels before, during, and after a 3-h constant infusion of alanine (2 mmol/(kg BW x h)). UNSR was estimated hourly as urinary excretion corrected for gut hydrolysis and accumulation in body water. The slope of the linear relationship between UNSR and amino-N concentration represents the hepatic kinetics of conversion of amino- to urea-N, and is denoted the functional hepatic nitrogen clearance (FHNC). RESULTS: Prenisolone, but not budesonide, administration increased basal blood and amino nitrogen concentrations (3.5 +/- 0.1 mmol/l (control) vs 3.8 +/- 0.1 mmol/l (prednisolone) (p<0.05) and 3.6 +/- 0.1 mmol/l (budesonide) (NS). Basal UNSR values were significantly increased following prednisolone (23.3 +/- 6.5 (control) vs 51.2 +/- 6.3 (prednisolone) (p<0.05)), while budesonide had no effect on basal UNSR (33.7 +/- 4.2 (budesonide) (NS)). Prednisolone administration increased FHNC (from 24.6 +/- 4.7 l/h (control) to 47.3 +/- 5.9 l/h (prednisolone) (p<0.05). Budesonide administration did not significantly increase FHNC (33.7 +/- 4.2 l/h (budesonide), (vs control; p=0.12, vs prednisolone: p<0.05)). CONCLUSIONS: Prednisolone administration led to increased levels of amino acids in blood and loss of N as urea, the latter in part due to a specific hepatic mechanism as shown by the increased FHNC. Budesonide led to unaltered levels of amino acids in blood, no changes in loss of N as urea, and unaltered hepatic kinetics for urea synthesis. Thus, oral budesonide administration had very limited effects on the hepatic contribution to nitrogen homeostasis and metabolism via urea synthesis, making treatment with budesonide superior to that of conventional glucocorticoids in this respect.     

Plasma endotoxin concentrations in patients with alcoholic and non-alcoholic liver disease: reevaluation with an improved chromogenic assay

Plasma endotoxin concentration was measured in 85 patients with alcoholic liver disease (alcoholic cirrhosis (n = 64), alcoholic hepatitis without cirrhosis (n = 11), fatty liver (n = 10), and in patients with non-alcoholic cirrhosis (n = 15]. Endotoxin concentration was determined with an improved chromogenic substrate assay, using individual standard curves for each plasma sample. In patients with alcoholic cirrhosis the mean endotoxin concentration was significantly higher than in patients with non-alcoholic cirrhosis (p less than 0.05). In addition, distinctly higher endotoxin concentrations (greater than 20 pg/ml) were more frequently observed in patients with alcoholic cirrhosis than in non-alcoholic cirrhosis (34.4 vs. 14.3%, p less than 0.05). Mean endotoxin concentration was not significantly higher in cirrhotics with ascites or esophageal varices as compared with the subgroup without ascites or esophageal varices. The endotoxin concentration did not correlate with serum bilirubin, prothrombin concentration or serum enzyme activities. In patients with alcoholic liver disease, however, endotoxin concentration revealed a negative correlation (p less than 0.05) with the concentration of high density lipoprotein cholesterol. On admission endotoxin concentrations in alcoholics with fatty liver were similarly elevated as observed in alcoholic cirrhosis. In six out of 12 patients with fatty liver or alcoholic hepatitis, in whom a second sample of plasma was investigated after 6 to 8 days, endotoxemia was no longer detectable; in the remaining patients, the endotoxin concentration decreased markedly. The results indicate that, irrespective of the stage of liver disease, alcohol abuse favours the development of endotoxemia. They support the hypothesis that gut-derived endotoxins might play a role in the initiation and aggravation of alcohol-induced liver disease.     

Effects of pancreatic hormones and glucocorticosteroids on argininosuccinate synthetase and argininosuccinase activities of rat liver during the perinatal period: in vivo and in vitro studies

The activity changes of two urea cycle enzymes, argininosuccinate synthetase (ASS) and argininosuccinase (ASL), were followed after corticosteroid and pancreatic hormone treatments in utero and in primary cultured fetal hepatocytes. The ASL activity which was induced by glucagon or by (Bu)2cAMP administration was enhanced by a treatment with streptozotocin for 2 days, although ASS was not changed under these conditions. The activity of both enzymes was enhanced by cortisol administration in utero only in streptozotocin-treated fetuses, suggesting an inhibitory effect of insulin. In cultured fetal hepatocytes, dexamethasone produced a marked increase of the two enzyme activities, which was abolished by the simultaneous addition of insulin. The parallel results obtained with these two experimental models allow one to conclude that the high plasma insulin level in late gestation might repress the development of ASS and ASL activities in utero and antagonize the effect of corticosteroids on these enzyme activities.     

Urea cycle enzyme activities are normal and inducible by a high-protein diet in CCl4 cirrhosis of rats

We produced moderately severe, inactive micronodular cirrhosis in rats using CCl4 and measured the urea cycle enzyme activities in liver after feeding a 15% casein diet for 1 week and again after a 60% casein diet for 1 week. There was no deficiency of any of the five urea cycle enzymes in cirrhotic livers of rats pair-fed the 15% casein diet. Argininosuccinate synthetase and carbamyl phosphate synthetase activities were lower than in non-pair-fed controls by some baselines. All five enzymes in cirrhotic livers were induced 1.5- to 3-fold by the high-protein diet expressed as units per 100 gm of rat. The level of carbamyl phosphate synthetase activity was lower in the livers of rats pair-fed the 60% casein diet than in control livers based on wet weight, collagen-free protein and DNA, but the activities were equal expressed as units per 100 gm of rat. This example of CCl4-induced cirrhosis in the rat does not serve as a good model for human cirrhosis, in which the urea cycle enzymes are reported to be decreased in activity.     

Lipopolysaccharide-induced tyrosine nitration and inactivation of hepatic glutamine synthetase in the rat

Glutamine synthetase (GS) in the liver is restricted to a small perivenous hepatocyte population and plays an important role in the scavenging of ammonia that has escaped the periportal urea-synthesizing compartment. We examined the effect of a single intraperitoneal injection of lipopolysaccharide (LPS) in vivo on glutamine synthesis in rat liver. LPS injection induced expression of inducible nitric oxide synthase, which was maximal after 6 to 12 hours but returned toward control levels within 24 hours. Twenty-four hours after LPS injection, an approximately fivefold increase in tyrosine-nitrated proteins in liver was found, and GS protein expression was decreased by approximately 20%, whereas GS activity was lowered by 40% to 50%. GS was found to be tyrosine-nitrated in response to LPS, and immunodepletion of tyrosine-nitrated proteins decreased GS protein by approximately 50% but had no effect on GS activity. Together with the finding via mass spectrometry that peroxynitrite-induced inactivation of purified GS is associated with nitration of the active site tyrosine residue, our data suggest that tyrosine nitration critically contributes to inactivation of the enzyme. In line with GS inactivation, glutamine synthesis from ammonia (0.3 mmol/L) in perfused livers from 24-hour LPS-treated rats was decreased by approximately 50%, whereas urea synthesis was not significantly affected. In conclusion, LPS impairs hepatic ammonia detoxification by both downregulation of GS and its inactivation because of tyrosine nitration. The resulting defect of perivenous scavenger cell function with regard to ammonia elimination may contribute to sepsis-induced development of hyperammonemia in patients who have cirrhosis.     

Evaluation of endogenous nitric oxide synthesis in congenital urea cycle enzyme defects

Nitric oxide (NO) is synthesized from arginine and O₂ by nitric oxide synthase (NOS). Citrulline, which is formed as a by-product of the NOS reaction, can be recycled to arginine by the 2 enzymes acting in the urea cycle: argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL). Although the complete urea cycle is expressed only in the liver, ASS and ASL are expressed in other organs including the kidney and vascular endothelium. To examine possible alterations of the NO pathway in urea cycle defects, we measured plasma concentrations of arginine and citrulline and serum concentrations of nitrite/nitrate (NOx⁻, stable NO metabolites) and asymmetric dimethylarginine (ADMA, an endogenous NOS inhibitor) in patients with congenital urea cycle disorders of 3 types: ornithine transcarbamylase (OTC) deficiency, ASS deficiency, and ASL deficiency. All were receiving oral arginine replacement at the time of this study. The same parameters were also measured in healthy subjects, who participated as controls. The OTC-deficient patients had significantly high NOx⁻ and nonsignificantly high ADMA concentrations. Their NOx⁻ was significantly positively correlated with arginine. The ASS-deficient patients had significantly low NOx⁻ and significantly high ADMA concentrations. The ASL-deficient patients had normal NOx⁻ and nonsignificantly high ADMA concentrations. In ASS-deficient and ASL-deficient patients, the NOx⁻ was significantly inversely correlated with citrulline. These results suggest that NO synthesis is enhanced in OTC-deficient patients while receiving arginine but that NO synthesis remains low in ASS-deficient patients despite receiving arginine. They also suggest that endogenous NO synthesis is negatively affected by citrulline and ADMA in ASS-deficient and ASL-deficient patients. Although the molecular mechanisms remain poorly understood, we infer that the NO pathway might play a role in the pathophysiology related to congenital urea cycle disorders.     

The hemochromatosis C282Y allele: a risk factor for hepatic veno-occlusive disease after hematopoietic stem cell transplantation

Hepatic veno-occlusive disease (HVOD) is a serious complication of hematopoietic stem cell transplantation (HSCT). Since the liver is a major site of iron deposition in HFE-associated hemochromatosis, and iron has oxidative toxicity, we hypothesized that HFE genotype might influence the risk of HVOD after myeloablative HSCT. We determined HFE genotypes in 166 HSCT recipients who were evaluated prospectively for HVOD. We also tested whether a common variant of the rate-limiting urea cycle enzyme, carbamyl-phosphate synthetase (CPS), previously observed to protect against HVOD in this cohort, modified the effect of HFE genotype. Risk of HVOD was significantly higher in carriers of at least one C282Y allele (RR=3.7, 95% CI 1.2-12.1) and increased progressively with C282Y allelic dose (RR=1.7, 95% CI 0.4-6.8 in heterozygotes; RR=8.6, 95% CI 1.5-48.5 in homozygotes). The CPS A allele, which encodes a more efficient urea cycle enzyme, reduced the risk of HVOD associated with HFE C282Y. We conclude that HFE C282Y is a risk factor for HVOD and that CPS polymorphisms may counteract its adverse effects. Knowledge of these genotypes and monitoring of iron stores may facilitate risk-stratification and testing of strategies to prevent HVOD, such as iron chelation and pharmacologic support of the urea cycle.     

Acute in Vivo Effects of Low Ethanol Concentration on the Capacity of Urea Synthesis in Rats

We studied the effect of acute exposure, by constant intravenous infusion, to a low blood ethanol concentration (range 8-14 mmol/l) on the in vivo capacity of urea-N synthesis (CUNS), alanine elimination, and the nitrogen retention in fed and fasted rats. Alanine was infused to obtain a constant blood concentration of alpha-amino nitrogen between 7.3 and 11.7 mmol/l, at which concentrations urea synthesis is at maximum. CUNS was calculated after nephrectomy as accumulation of urea in body water, elimination of alanine as alanine infusion rate corrected for accumulation, and nitrogen retention as the difference. In the fed state ethanol decreased CUNS from 7.84 +/- 0.32 mumol N/(min 100 g body weight (BW] (mean +/- SEM) (n = 7) to 6.30 +/- 0.58 (n = 6) (p less than 0.001) and in the fasted state from 8.25 +/- 0.27 mumol N/(min 100 g BW) (n = 10) to 6.90 +/- 0.25 (n = 10) (p less than 0.001). In the fed state ethanol increased the elimination of alanine from 6.49 +/- 0.28 mumol/(min 100 g BW) (n = 7) to 6.95 +/- 0.25 (n = 6) (p less than 0.01), and in the fasted state decreased it from 6.25 +/- 0.12 mumol/(min 100 g BW) (n = 10) to 5.67 +/- 0.20 (n = 10) (p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth hormone and growth hormone secretagogue effects on nitrogen balance and urea synthesis in steroid treated rats

ObjectivesGrowth hormone (GH) reduces the catabolic side effects of steroid treatment via effects on the amino-nitrogen metabolism. Ipamorelin is a synthetic peptide with GH releasing properties. We wished to study the metabolic effects of Ipamorelin and GH on selected hepatic measures of α-amino-nitrogen conversion during steroid-induced catabolism.DesignFive groups of rats were included: (1) free-fed controls (2) pair-fed controls (3) prednisolone (delcortol, 4 mg × kg^?1 × day^?1) (4) prednisolone and GH (1 mg × kg^?1 × day^?1) (5) prednisolone and Ipamorelin (0.5 mg × kg^?1 × day^?1). After seven days the hepatic capacity of urea-N synthesis (CUNS) was determined in parallel with measurements of liver mRNA levels of urea cycle enzymes, whole-body N-balance, and N-contents of various organs.ResultsCompared to pair-fed controls, prednisolone increased CUNS (p < 0.01) as well as the expression of urea cycle genes (p < 0.01), and decreased N-balance (p < 0.01) as well as organ N-contents (p < 0.05). Compared to prednisolone treated animals, co-administration of GH reduced CUNS by 33% (p < 0.01), normalized urea cycle gene expression, improved N-balance 2.5-fold, and normalized or improved organ N-contents. In prednisolone treated rats Ipamorelin reduced CUNS by 20% (p < 0.05), decreased the expression of urea cycle enzymes, neutralised N-balance, and normalized or improved organ N-contents.ConclusionAccelerated nitrogen wasting in the liver and other organs caused by prednisolone treatment was counteracted by treatment with either GH or its secretagogue Ipamorelin, though at the doses given less efficiently by the latter. This functional study of animals confirms that the GH secretagogue exerts GH related metabolic effects and may be useful in the treatment of steroid-induced catabolism.     

Analysis of the deterioration rates of liver function in cirrhosis, based on galactose elimination capacity

The prognosis of cirrhotic patients may depend on their liver function, but very few data are available to predict life expectancy in individual subjects on the basis of their liver function tests. The yearly changes in liver function, based on galactose elimination capacity (GEC), were retrospectively analyzed in 76 cirrhotic patients. The first GEC measurement had always been performed at the time of diagnosis. From that time on, mean GEC changes (in mmol/min per year) were +0.13 [SD 0.60] in the 1st year (range: +1.42/-1.35), and -0.03 [0.30] in the 2nd year (P = ns). Only after 36 months could a significant deterioration in liver function be demonstrated, but GEC changes still ranged from +0.14 to -0.35. The trend in liver function was similar in patients with alcoholic and non-alcoholic cirrhosis, but in alcoholics a favourable effect of abstinence was proved. In individual subjects, 2 consecutive GEC measurements, at least 6 months apart, failed to predict the following GEC values. The coefficients of determination between expected and measured GEC or delta GEC were 0.13 and 0.36, respectively (n = 58). When forecasting was limited to 2 years (n = 38), still only 31% and 55% of GEC values and delta GEC variance was predictable on the basis of preceding GEC values. The study shows that no definite trends in liver function deterioration rates can be observed in cirrhosis. This limits the usefulness of liver function tests in predicting prognosis in cirrhotic patients.     

急性肝功能衰竭大鼠内毒素血症对肝脏和肾脏糖异生功能的影响

目的探讨大鼠急性肝功能衰竭时内毒素血症对肝脏及肾脏糖异生功能及血糖水平的影响。方法24只雄性健康成年SD大鼠,随机分成4组,每组6只,Ⅰ组：腹腔注射等渗盐水,Ⅱ组：腹腔注射400 mg/kg D-氨基半乳糖（D-GaLN）;Ⅲ组：腹腔注射400 mg/kg D- GaLN＋50μg/kg LPS,Ⅳ组：腹腔注射400 mg/kg D-GaLN＋500μg/kg LPS。LPS注射后6 h,取血清检测内毒素、肾功能,取大鼠肝组织及肾组织,采用荧光定量PCR方法检测磷酸烯醇丙酮酸磷酸羧激酶（PEPCK）基因表达。结果Ⅰ组、Ⅱ组大鼠未见明显的内毒素血症,Ⅲ组、Ⅳ组大鼠体内内毒素水平明显升高,Ⅳ组高于Ⅲ组（8.05±0.43对比3.50±2.25,P〈0.05）。Ⅰ组、Ⅱ组、Ⅲ组大鼠于LPS注射前后未出现低血糖,Ⅳ组大鼠于LPS注射后6h出现明显的低血糖。各组大鼠肾功能均在正常水平,仅有Ⅳ组大鼠出现血清尿素氮水平轻度增高。大鼠肝脏PEPCK的表达在Ⅰ组、Ⅱ组、Ⅲ组、Ⅳ组逐渐减少,差异有统计学意义（2.54±1.32、1.87±0.15、0.91±0.13、0.44±0.42,P〈0.05）;大鼠肾脏PEPCK的表达,同Ⅰ组比较,Ⅱ组无明显变化（0.75±0.03对比0.77±0.04,P〉0.05）,Ⅲ组明显增强（0.75±0.03对比1.63±0.86,P〈0.05）,Ⅳ组大鼠肾脏PEPCK表达显著减弱（0.75±0.03对比0.13±0.07,P〈0.05）。结论急性肝功能衰竭大鼠中严重的内毒素血症通过抑制PEPCK的转录损伤肝脏和肾脏糖异生的功能,导致低血糖的发生。