Heat shock protein 70 in rat liver with necrosis and regeneration induced by thioacetamide

Heat shock protein (hsp), which changes both its concentration and localization in reaction to stresses such as heating, ischemia, etc., is thought to protect protein structure and act as a chaperone in intracellular transportation. We examined one of the hsps, hsp 70, in rat liver with necrosis and regeneration produced by thioacetamide (TAA). Hsp 70 was determined by immunoblotting and detected histologically by immunostaining, using a specific antibody. Generally, hsp 70 moves from the cytosol to the nucleus, where it concentrates 15 min after TAA injection. After 15 min, hsp 70 was not detected in the nuclei of hepatocytes around the central vein, where the hepatocytes olater became necrotic. However, hsp 70 immunostaining was increasingly strong in the nuclei of hepatocytes around the portal area, which did not become necrotic. These findings show that, in acute necrosis, hsp 70 seems to correlate with nuclear protection or with the transportation of some protein from the cytosol to the nucleus. Hepatocytes probably neither survive nor regenerate without hsp 70 in their nuclei.     

热缺血供肝耐受冷保存时限的实验研究

心脏停搏供体是肝移植供肝来源的重要途径之一。有研究表明，热缺血30min以内的供肝可考虑应用，但此类供肝本身存在热缺血损伤，在后续的威斯康星大学溶液（UW液）中能冷保存多久能为临床所用尚未可知。本实验探讨了存在热缺血10min的供肝在UW液中冷保存的安全时限。     

Changes in rat liver gene expression induced by thioacetamide: Protective role of S-adenosyl-L-methionine by a glutathione-dependent mechanism

Chronic liver damage induced by thioacetamide (TAM) was accompanied by changes in the expression of genes related to growth (beta-actin) and function (albumin and haptoglobin) of the liver. Their messenger RNA (mRNA) levels increased during the first days after TAM administration, but 4 to 7 days after prolonged treatment with this drug, liver gene expression was considerable decreased. TAM-induced changes in albumin and beta-actin mRNA levels were prevented by cotreatment with S-adenosyl-L-methionine (SAM). We have investigated the possible involvement of glutathione in the protective mechanism of SAM. Firstly, we found that TAM treatment in the rat induced changes in liver glutathione disulfide (GSSG) levels, with a concomitant increase in the glutathione reductase enzymatic activity, these changes being abolished when animals were cotreated with TAM and SAM. Secondly, when rats were pretreated with buthionine sulfoximine (BSO), a glutathione synthesis inhibitor, before thioacetamide administration, the beneficial effect of SAM on liver gene expression was completely abolished. These results were confirmed by assaying the alanine transaminase serum activity, a parameter of liver injury. TAM-treated animals had increases in this serum enzyme, this effect being partially blocked by SAM. However, in BSO-pretreated rats, the protective effect of SAM was impaired. Taking together all these results, we propose a glutathione-dependent mechanism in the SAM protection against TAM hepatotoxicity in the rat. (Hepatology 1996 Mar;23(3):600-6)     

Chronic liver injury by thioacetamide and promotion of hepatic carcinogenesis

Summary To verify whether a mild, but prolonged liver injury by chemicals needing bioactivation causes both hepatic cirrhosis and the appearance of hepatocyte nodules and tumors (providing the liver has been exposed previously to initiating stimuli), diethylnitrosamine-initiated and uninitiated rats were administered thioacetamide at low dose (250 mg/l drinking water) for 6 months. Hepatocyte nodule incidence as well as changes in the drug-metabolizing system were followed at monthly intervals. In the uninitiated rats a micronodular liver cirrhosis slowly developed upon thioacetamide chronic administration; a few hepatocyte focal lesions of small size were seen from the 3rd month onward. By contrast in the diethylnitrosamine-initiated thioacetamide-treated rats the liver was macronodular because of the appearance and growth of many hepatocyte nodules; some hepatomas were also seen. During thioacetamide administration both uninitiated and diethylnitrosamine-initiated rats underwent a progressive decrease of the cytochrome P-450 liver content as well as of the activity of aminopyrine N-demethylase, ethoxycoumarin O-deethylase and ethoxyresorufin O-deethylase. On the other hand, most components of the phase II of the drug-metabolizing system were markedly enhanced. In conclusion, chronic administration of thioacetamide at low doses provided strong promoting stimuli for previously initiated hepatocytes.     

Hemodynamic characterization in experimental liver cirrhosis induced by thioacetamide administration

Systemic and splanchnic hemodynamics in experimental liver cirrhosis in rats induced by thioacetamide were evaluated by the radioactive microsphere method. Cardiac output and regional blood flow were measured in conscious and anesthetized control and cirrhotic rats. The conscious thioacetamide-treatment rats had hyperdynamic circulation with an increased cardiac index (300±10 vs 258±3 ml/min/kg body weight,P<0.001) and increased portal venous inflow compared with the controls (64.60±2.4 vs 48.39±0.88 ml/min/kg body weight,P<0.001). Under pentobarbital anesthesia, the hyperdynamic circulation of the cirrhotic rats was maintained, with an increased cardiac index (276±7 vs 229±5 ml/min/kg body weight,P<0.001) and increased portal venous inflow compared with the controls (72.47±3.0 vs 54.08±1.2 ml/min/kg body weight,P<0.001). Portal pressure, portal venous resistance, and portal systemic shunting increased significantly while splanchnic arterial resistance decreased significantly in cirrhotic rats. Thioacetamide-induced cirrhosis is a useful model for the hemodynamic study of portal hypertension and remains useful in hemodynamic studies in the basal state under pentobarbital anesthesia.     

Melatonin prevents experimental liver cirrhosis induced by thioacetamide in rats

Abstract:  Liver cirrhosis is a critical stage of chronic liver diseases that can produce liver failure, portal hypertension and hepatocarcinoma. Sustained oxidative stress plays a key role in cell damage and fibrosis induced during liver cirrhosis. We evaluated the effect of oxidative stress regulation by melatonin on the development of parenchymal destruction and stellate cell activation in experimental liver cirrhosis. Melatonin was administered to rats with liver cirrhosis induced by thioacetamide (TAA) for 1 or 3 months. Liver injury was assessed by serological analysis, as well as hematoxylin-eosin staining and the in situ apoptosis detection assay in liver sections. Oxidative stress was evaluated by lipoperoxide and reduced glutathione levels, and by the measurement of catalase and superoxide dismutase activities in liver and serum respectively. The activation of stellate cells was evaluated by α -smooth muscle actin expression in liver sections. Our results showed that TAA induced oxidative stress with extensive tissue damage and enhanced α -smooth muscle actin expression in liver. Melatonin prevented the oxidative stress-related changes associated with TAA toxicity. In conclusion, the study showed that melatonin prevents the tissue damage and fibrosis associated with TAA-induced liver cirrhosis in rats.     

硫代乙酰胺致大鼠肠源性内毒素血症模型探讨

目的 探讨不同剂量硫代乙酰胺(TAA)所制备的大鼠肠源性内毒素血症(IETM)模型的量效关系.方法 将40只大鼠分为4组,每组10只.TAA组分别以200、400、600mg/kg剂量的TAA灌胃,24h后相同剂量TAA重复灌胃一次,建立不同剂量TAA致大鼠IETM的动物模型;健康对照组以等体积0.9%氯化钠溶液灌胃.观察造模后24、48h大鼠死亡情况,48h后采集存活大鼠腹主动脉血,检测血浆内毒素、血清ALT和AST,观察肝组织病理变化.采用单因素方差分析,组间比较采用t检验.结果 造模48h后,健康对照组无大鼠死亡,200mg/kgTAA模型组死亡2只,400mg/kg TAA模型组死亡5只,600mg/kg TAA模型组死亡8只.200、400、600mg/kg TAA模型组大鼠血清ALT水平分别为(305.09±116.78)、(901.67±274.31)和(1454.84±473.49)U/L,明显高于健康对照组的(47.81±22.61)U/L(t=14.583、25.896、20.596,均P＜0.05);200、400、600mg/kg TAA模型组大鼠血清AST水平分别为(465.88±139.96)、(884.37±250.90)和(1889.23±159.67)U/L,明显高于健康对照组的(69.33±22.04)U/L(t=12.988、18.455、13.542,均P＜0.05);200、400、600mg/kg TAA模型组大鼠血浆内毒素水平分别为(0.436±0.110)、(0.550±0.095)和(0.620±0.057)EU/mL,明显高于健康对照组的(0.103±0.056)EU/mL(t=7.335、5.260、8.191,均P＜0.05).病理学显示不同剂量TAA模型组有不同程度的肝细胞变性坏死.结论 TAA剂量为200～600mg/kg时可成功制作IETM模型,200mg/kg TAA模型组大鼠死亡率较低,适于进一步的实验研究.     

慢性间歇低氧对大鼠肝细胞SOCS3表达的影响

目的通过构建慢性间歇低氧大鼠模型,检测模型大鼠空腹血糖、胰岛素水平及胰岛素抵抗指数并检测大鼠肝细胞SOCS3蛋白及其mRNA表达量的变化,探讨慢性间歇低氧对胰岛素抵抗的影响。方法选取健康雄性SD大鼠24只,按随机数字表法分为正常对照组（NC组）、慢性间歇低氧2周组（CIH2组）、慢性间歇低氧5周组（CIH5组）,每组8只。NC组无间歇低氧暴露,CIH2组、CIH5组暴露于间歇低氧环境中（每日8h,舱内最低氧浓度为6％～7％）。分别于第15天、第36天测定大鼠空腹血糖、放射免疫法测空腹胰岛素水平并按稳态模型评估法（HOMA）计算胰岛素抵抗指数,SABC法免疫组织化学试剂盒检测大鼠肝细胞SOCS3蛋白表达,以平均灰度值表示SOCS3蛋白表达量,荧光定量-PCR法检测SOCS3-mRNA基因表达量。结果与NC组比较,CIH2与CIH5组空腹血糖水平（差异有统计学意义,F=33．582,P〈0．05）、胰岛素水平（差异有统计学意义,F=35．633,P〈0．05）及HOMAIR（差异有统计学意义,F=49．045,P〈0．05）升高,且CIH5组最为显著（P〈0．05）;与NC组比较,CIH2与CIH5组SOCS3蛋白表达升高（差异有统计学意义,F-9．472,PG0．05）,CIH2与CIH5组差异无统计学意义（P〉0．05）;与NC组及CIH2组比较,CIH5组SOCS3-mRNA表达升高（差异有统计学意义,F=8．665,P〈0．05）,CIH2组升高不明显（差异无统计学意义,P〉0．05）。Pearson相关分析显示HOMA—IR与sOCS3平均灰度值呈负相关（r=-0．759,P〈0．001）,HOMA-IR与SOCS3-mRNA呈正相关（r=-0．603,P=0．01）。结论①CIH暴露使大鼠胰岛素水平及血糖水平升高且发生胰岛素抵抗,且随间歇低氧暴露时间延长,胰岛素抵抗程度加重。②CIH导致大鼠肝细胞内SOCS3蛋白表达增高,SOCS3-mRNA基因表达上调,CIH可能通过SOCS3参与了胰岛素抵抗的发生发展。     

肠源性内毒素血症在硫代乙酰胺所致肝损伤发病中的作用

目的探讨肠源性内毒素血症在硫代乙酰胺（thioacetamide,TAA）所致肝损伤模型发病机制中的地位和作用。方法选用雄性Wistar大鼠26只,随机分为4组,即正常组（N）及结肠切除（C）对照组;TAA损伤组（T）和结肠切除+TAA组（C+T）。采用生化检测法测定血浆内毒素含量和ALT活性。结果单纯给予TAA组,血浆内毒素水平和ALT活性显著高于其它三个组;而结肠切除+TAA组的血浆内毒素水平与结肠切除对照组和正常对照组相比无明显升高,ALT活性结肠切除组+TAA组和正常对照组比较明显升高,但比TAA组却明显减低。T组与C+T组血浆内毒素水平与ALT活性变化之间呈正相关关系（r＝0.985,P＜0.01）。结论TAA所导致的内毒素血症是肠源性内毒素血症;TAA本身有直接致肝细胞损伤的作用,但其所形成的肠源性内毒素血症造成的肝损伤更为严重。     

慢性脑缺血神经胶质细胞损伤与血管性痴呆的研究进展

慢性脑缺血是指各种原因引发的长期脑血流灌注不足，是血管性痴呆（vascular dementia VD）、Binswanger病等多种脑血管疾病发生发展过程中的一个共同病理过程。临床上主要表现为渐进性的痴呆，学习记忆和空间辨别能力明显下降。神经病理方面的改变除了神经元的变性和坏死外，还有胶质细胞的攻变：近年的研究证明，慢性脑缺血后神经胶质细胞的活动异常活跃，缺血性脑损伤所激发的神经胶质细胞反应极其复杂，已经远远超出了对神经元的营养作用和清除变性坏死组织的范围。     

Subcellular redistribution of protein kinase C isozymes is associated with rat liver cirrhotic changes induced by carbon tetrachloride or thioacetamide

BACKGROUND AND AIMS: Protein kinase C (PKC) plays a key role in the alteration of signal transduction in the liver, which may contribute to the development of liver cirrhosis. The aim of the present study was to examine the subcellular redistribution of PKC isozymes in rat liver cirrhosis, which is induced by two different cirrhotic chemical agents, carbon tetrachloride (CCl4) and thioacetamide (TAA). METHODS AND RESULTS: Thioacetamide and CCl4 were administered to rats for 8 and 30 weeks, respectively before rats were killed and autopsies performed at 9, 20 and 30 weeks later. The TAA induced a fibrotic pattern in the liver that differed from that produced by CCl4, notably in the formation of fibrous connective tissue and the proliferation of bile ductule cells. Cholangiofibrosis and clear-cell foci were also observed in TAA-treated rats at 30 weeks. Histological examination revealed that severe cirrhotic changes were present 9 weeks after the commencement of CCl4 treatment and 30 weeks after TAA treatment. DISCUSSION: When the subcellular redistribution of PKC isozymes (PKCalpha, -beta1, -delta, and -epsilon) was examined, all the PKC isozymes in CCl4-treated rats were found to be translocated to the membrane fraction, which may mean PKC activation, and then downregulated by proteolytic degradation after 9 weeks of treatment, which coincided with peak cirrhotic changes. All rats treated with CCl4 recovered to the control level after 20 weeks of treatment. In the case of TAA-treated rats, PKC isozymes were translocated to the particulate fraction of the liver after 9 weeks of treatment and this persisted in most of the rats for the duration of the experiment. CONCLUSIONS: From these results, it would appear that PKC translocation preceded morphologic changes, and that an altered subcellular distribution of the PKC isozyme may be associated with the response to liver damage and carcinogenesis.     

Chronic intermittent hypoxia predisposes to liver injury

Obstructive sleep apnea (OSA) is characterized by chronic intermittent hypoxia (CIH). OSA is associated with nonalcoholic steatohepatitis (NASH) in obese subjects. The aim of this study was to investigate the effects of CIH on the liver in the absence of obesity. Lean C57BL/6J mice (n = 15) on a regular chow diet were exposed to CIH for 12 weeks and compared with pair-fed mice exposed to intermittent air (IA, n = 15). CIH caused liver injury with an increase in serum ALT (224 +/- 39 U/l versus 118 +/- 22 U/l in the IA group, P < 0.05), whereas AST and alkaline phosphatase were unchanged. CIH also induced hyperglycemia, a decrease in fasting serum insulin levels, and mild elevation of fasting serum total cholesterol and triglycerides (TG). Liver TG content was unchanged, whereas cholesterol content was decreased. Histology showed swelling of hepatocytes, no evidence of hepatic steatosis, and marked accumulation of glycogen in hepatocytes. CIH led to lipid peroxidation of liver tissue with a malondialdehyde (MDA)/free fatty acids (FFA) ratio of 0.54 +/- 0.07 mmol/mol versus 0.30 +/- 0.01 mmol/mol in control animals (P < 0.01), and increased levels of active nuclear factor kappaB (NF-kappaB) in the nuclear fraction of hepatocytes, suggesting that CIH induced oxidative stress in the liver. Finally, CIH greatly exacerbated acetaminophen-induced liver toxicity, causing fulminant hepatocellular injury. CONCLUSION: In the absence of obesity, CIH leads to mild liver injury via oxidative stress and excessive glycogen accumulation in hepatocytes and sensitizes the liver to a second insult, whereas NASH does not develop.     

Leptin is required for fibrogenic responses induced by thioacetamide in the murine liver

In this study, we investigated hepatic fibrogenesis caused by long-term thioacetamide (TAA) administration in ob/ob mice, a naturally occurring leptin deficient animal. In the lean littermates, prominent hepatic fibrosis, as well as positive staining for alpha smooth muscle actin (alpha-SMA), was induced by treatment with TAA (200 microg/g, IP, 3 times per week) for 4 to 8 weeks as expected. In sharp contrast, almost no hepatic fibrosis developed in ob/ob mice given the equivalent doses of TAA, where specific staining for alpha-SMA barely was detected. Induction of alpha1(I) procollagen mRNA caused by TAA also was prevented in ob/ob mice almost completely. Further, transforming growth factor beta (TGF-beta) mRNA was increased in the liver after TAA treatment for 4 weeks in lean littermates, which also was prevented in ob/ob mice. Interestingly, fibrotic septa in the hepatic lobules, as well as increases in alpha1(I) procollagen mRNA, was observed in ob/ob mice, when they were injected with recombinant murine leptin (1 microg/g daily) in combination with TAA treatment. Leptin per se did not cause any fibrotic changes in the liver in ob/ob mice. These findings clearly indicated that leptin deficiency is responsible for the resistance to TAA-induced profibrogenic responses in ob/ob mice. In conclusion, leptin appears to promote profibrogenic responses in the liver, in part, by up-regulation of TGF-beta.     

Reabsorption of iron into acutely damaged rat liver: A role for ferritins

AIM To studied iron metabolism in liver, spleen, and serum after acute liver-damage, in relation to surrogate markers for liver-damage and repair.METHODS Rats received intraperitoneal injection of the hepatotoxin thioacetamide(TAA), and were sacrificed regularly between 1 and 96 h thereafter. Serum levels of transaminases and iron were measured using conventional laboratory assays. Liver tissue was used for conventional histology, immunohistology, and iron staining. The expression of acute-phase cytokines, ferritin light chain(FTL), and ferritin heavy chain(FTH)was investigated in the liver by q RT-PCR. Western blotting was used to investigate FTL and FTH in liver tissue and serum. Liver and spleen tissue was also used to determine iron concentrations.RESULTS After a short initial decrease, iron serum concentrations increased in parallel with serum transaminase(aspartate aminotransferase and alanine aminotransferase) levels, which reached a maximum at 48 h, and decreased thereafter. Similarly, after 48 h a significant increase in FTL, and after 72 h in FTH was detected in serum. While earliest morphological signs of inflammation in liver were visible after 6 h, increased expression of the two acute-phase cytokines IFN-γ(1 h) and IL-1β(3 h) was detectable earlier, with maximum values after 12-24 h. Iron concentrations in liver tissue increased steadily between 1 h and 48 h, and remained high at 96 h. In contrast, spleen iron concentrations remained unchanged until 48 h, and increased mildly thereafter(96 h). Although tissue iron staining was negative, hepatic FTL and FTH protein levels were strongly elevated. Our results reveal effects on hepatic iron concentrations after direct liver injury by TAA. The increase of liver iron concentrations may be due to the uptake of a significant proportion of the metal by healthy hepatocytes, and only to a minor extent by macrophages, as spleen iron concentrations do not increase in parallel. The temporary increase of iron, FTH and transaminases in serum is obviously due to their release by damaged hepatocytes.CONCLUSION Increased liver iron levels may be the consequence of hepatocyte damage. Iron released into serum by damaged hepatocytes is obviously transported back and stored via ferritins.     

Tolerance to ischemia of hypertrophied human hearts during valve replacement

Summary This study evaluates the tolerance to ischemia during induced cardiac arrest in patients undergoing aortic valve replacement. In all patients cardiac standstill was of 45 minutes duration. Biopsies for electron microscopic study were taken from the left ventricle before induction of arrest, at the end of the ischemic period and 20 minutes after coronary perfusion had been reestablished. Structural ischemic damage was more pronounced in patients with severe hypertrophy and structural reconstitution was delayed. Degenerative changes of the myocardial cells, although observed frequently, apparently did not influence the tolerance to ischemia. It is concluded from this study that patients with severe hypertrophy represent a high-risk group in cardiac surgery because of their reduced tolerance to induced myocardial ischemia during cardiopulmonary bypass.

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Die Ischämietoleranz des menschlichen hypertrophierten Herzens während Operationen zum Ersatz der Aortenklappe

Zusammenfassung Wir untersuchten in dieser Arbeit die Ischämietoleranz hypertrophierter Herzen bei künstlich induziertem Herzstillstand während Operationen in totalem kardiopulmonalem Bypass. Bei allen Patienten dauerte der Herzstillstand 45 Minuten. Für die elektronenmikroskopische Untersuchung wurden Biopsien aus dem linken Ventrikel zu folgenden Zeitpunkten entnommen: vor der Einleitung des Herzstillstandes, am Ende des ischämischen Intervalls und 20 Minuten nach Wiederherstellung der Koronarperfusion.Die feinstrukturelle Beschädigung des Myokards, verursacht durch die Ischämie, nahm zu mit dem Schweregrad der Hypertrophie, desgleichen war die Wiederherstellung der strukturellen Schäden verzögert bei stärkerer Hypertrophie.Die häufig vorhandenen degenerativen Veränderungen im Herzmuskel beeinflußten die Ischämietoleranz nicht.Aus diesen Resultaten ergibt sich, daß Patienten mit kardialer Hypertrophie mittleren bis schweren Grades eine Risikogruppe für die Herzchirurgie darstellen, da ihre Ischämietoleranz eingeschränkt ist.

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With 16 figures and 3 tables     

链激酶对大鼠肝脏缺血再灌注损伤的保护作用

目的:研究链激酶对大鼠肝脏缺血再灌注损伤的保护作用.方法:36只Wistar大鼠随机分成3组,每组12只.对照组大鼠肝脏经门脉10 mL乳酸林格液灌洗后,低温4℃UW液中保存24h.实验组大鼠肝脏经含链激酶7500 IU乳酸林格灌洗后,分别低温或低温静脉持续氧气灌注保存24 h后.离体常温再灌注45 min,观察灌洗液谷氨酰胺丙氨酸转氨酶(alanine aminotransferase.ALT)、谷氨酸乳酸脱氢酶(glutamate-lactate dehydrogenase,GLDH)和嘌呤核苷磷酸化酶(purine nucleoside phosphorylase,PNP)活性及肝脏胆汁分泌量、肝组织5'核苷酸酶活性的变化.结果:实验组再灌注过程中灌洗液ALT、GLDH和PNP活性均明显降低于对照组(P＜0.05或P＜0.01);胆汁分泌量增加[3.7±0.7μL/(g·45 min),9.1±0.μL/(g·45 min)vs1.1±0.9μL/(g·45 min),P＜0.05,P＜0.01);5'核苷酸酶活性染色明显增强.结论:链激酶改善低温保存肝脏的微循环,减轻缺血再灌注损伤.     

Tolerance of rat duodenum to luminal acid

The tolerance of the duodenal mucosa to luminal acid was investigated by measuring with a liquid sensor pH microelectrode technique the epithelial surface pH (pH_s) and subepithelial tissue pH (pH_t) in rat proximal (duodenal bulb, Brunner gland area) and distal duodenum exposed to luminal acid. Under basal conditions, pH_s was roughly equal in both parts of the duodenum; proximal duodenum, 7.40 ± 0.14 (mean ± sem) at the villus tip and 7.54 ± 0.16 at the depth of crypt; distal duodenum, 7.46 ± 0.19 and 7.55 ± 0.09, respectively. Yet, exposure of the mucosa to luminal acid (10 mM HCl) provoked a significantly lesser decrease of pH_s (0.25 ± 0.13 vs 0.42 ± 0.12 pH units) in the proximal duodenum, suggesting that the response of epithelial HCO₃ secretion to luminal acid is stronger in that part of the duodenum. Further, the initial acidification of pH_s was followed in the proximal duodenum by a secondary alkalinization of pH_s, leading to normalization of pH_s, which may suggest activation of compensatory protective mechanisms. pH_t at the villus tip was likewise roughly equal in both parts of duodenum (7.29 ± 0.05 vs 7.17 ± 0.04), but, again, acidification of the luminal perfusate progressively from 10 to 100 mM HCl induced a much earlier and significantly more profound acidification in the distal than in the proximal duodenum. The possible contribution of Brunner glands to the greater mucosal tolerance to acid in the proximal duodenum was assessed by investigating whether stimulation or inhibition of Brunner gland secretion modulates the response of the duodenal mucosa to acid. It appeared that even though stimulation of Brunner gland secretion by secretin increased slightly but significantly pH_s (0.10 ± 0.03 pH units), it did not alleviate intramucosal acidosis during exposure to luminal acid. In contrast, inhibition of Brunner gland secretion by somatostatin had no influence on pH_s but markedly enhanced the susceptibility of the mucosa to tissue acidosis during acid exposure. This suggests that Brunner glands may, indeed, have a role in the mucosal defense against acid but that this protective action is mediated by some other mechanisms than stimulation of alkaline secretion. The data indicate that the proximal duodenum has a greater tolerance against luminal acid than distal duodenum, presumably due to a stronger stimulatory response of HCO₃ secretion to luminal acid. In addition, the action of the Brunner glands may contribute to the enhanced capacity of the proximal duodenum to withstand luminal acid.This study was supported by grants from the Medical Research Council of the Academy of Finland, Sigrid Jusélius Foundation, and University of Helsinki, Helsinki, Finland.     

Tolerance to disulfiram induced by chronic alcohol intake in the rat

Background: Disulfiram, an inhibitor of aldehyde dehydrogenase used in the treatment of alcoholism, is an effective medication when its intake is supervised by a third person. However, its therapeutic efficacy varies widely, in part due to the fact that disulfiram is a pro‐drug that requires its transformation into an active form and because it shows a wide range of secondary effects which often prevent the use of doses that ensure full therapeutic effectiveness. In this preclinical study in rats we report the development of tolerance to disulfiram induced by the chronic ingestion of ethanol, an additional source of variation for the actions of disulfiram with possible therapeutic significance, We also addresses the likely mechanism of this effect. Methods: Wistar‐derived rats bred for generations as high ethanol drinkers (UChB) were trained for either 3 days (Group A) or 30 days (Group B) to choose between ethanol (10% v/v) or water, which were freely available from 2 bottles on a 24‐hour basis. Subsequently, animals in both groups were administered disulfiram or cyanamide (another inhibitor of aldehyde dehydrogenase) and ethanol intake in this free choice paradigm was determined. Animals were also administered a standard dose of 1 g ethanol/kg (i.p) and arterial blood acetaldehyde was measured. Results: Disulfiram (12.5 and 25 mg/kg) and cyanamide (10 mg/kg) markedly inhibited ethanol intake (up to 60 to 70%) in animals that had ethanol access for only 3 days (Group A). However both drugs were inactive in inhibiting ethanol intake in animals that had consumed ethanol for 30 days (Group B). Following the injection of 1 g ethanol/kg, arterial blood acetaldehyde levels reached levels of 150 and 300 μM for disulfiram and cyanamide respectively, values which were virtually identical regardless of the length of prior ethanol intake of the animals. Conclusions: Chronic ethanol intake in high‐drinker rats leads to marked tolerance to the aversive effects of disulfiram and cyanamide on ethanol intake despite the presence of consistently high levels of blood acetaldehyde. These findings may have implications for the use of disulfiram for the treatment of alcoholism in humans.