Different susceptibility to the development of nitroglycerin tolerance in the arterial and venous circulation in humans. Effects of N-acetylcysteine administration.

BACKGROUND. Tolerance to the effects of organic nitrates develops rapidly during continuous exposure to these drugs; its main mechanism seems to be an intracellular sulfhydryl group depletion. However, the relative susceptibility to the development of nitroglycerin tolerance of the arterial or venous circulation in humans is still a matter of dispute. METHODS AND RESULTS. Twenty patients with coronary artery disease underwent a continuous 24-hour nitroglycerin infusion followed by a bolus administration of N-acetylcysteine. Forearm blood flow (ml/100 ml/min) and venous volume (ml/100 ml) were measured by strain gauge plethysmography under control conditions, at the end of nitroglycerin titration, after 24-hour infusion, and after N-acetylcysteine; vascular resistance was calculated as mean cuff blood pressure divided by flow. After 24 hours of nitroglycerin infusion, the initial increase in venous volume was reduced 48% (p less than 0.01), whereas the acute effects on vascular resistance were not attenuated in the whole group. N-Acetylcysteine completely restored nitroglycerin venodilator effects in all 10 patients in whom attenuation of the venous effects was observed during the infusion period. CONCLUSIONS. The data indicate that the susceptibility to the development of nitrate tolerance in humans is higher in the venous than in the arterial circulation, and that the sulfhydryl group donor N-acetylcysteine is extremely effective in reversing nitroglycerin tolerance in the venous circulation in humans.     

Nitrate tolerance in epicardial arteries or in the venous system is not reversed by N-acetylcysteine in vivo, but tolerance-independent interactions exist

N-acetylcysteine is assumed to reverse nitrate tolerance by replenishing depleted intracellular sulfhydryl groups, but data on interactions of N-acetylcysteine and nitrates in patients with stable angina are controversial and disappointing. Therefore, we studied the effect of N-acetylcysteine on nitrate responsiveness of epicardial arteries and of the venous system (assessed as changes in effective vascular compliance) in dogs (n = 12) during long-term nitroglycerin treatment (1.5 micrograms/kg/min i.v. for 5-6 days). In dogs with nitroglycerin-specific tolerance (shift of venous or epicardial artery dilation to 15-17-fold higher dosages), N-acetylcysteine (100 mg/kg i.v.) had no dilator effect and did not alter the dose-response relations of nitroglycerin. Yet, in nontolerant dogs (n = 17), N-acetylcysteine augmented (1.5-2.0-fold) the dilation of epicardial arteries and the reduction of peripheral vascular resistance induced by 0.5-1.5 micrograms/kg/min nitroglycerin. In vitro, the augmentation of purified guanylate cyclase activity by nitroglycerin (10-100 microM) was potentiated by N-acetylcysteine (0.01-1.0 mM) in saline or in canine plasma, but N-acetylcysteine alone was ineffective. We conclude that 1) N-acetylcysteine does not restore nitroglycerin responsiveness in tolerant epicardial arteries or veins in vivo, 2) a small, tolerance-independent augmentation of nitroglycerin-induced dilation may result from N-acetylcysteine-induced extracellular formation of a stimulant of guanylate cyclase from nitroglycerin.     

Evidence for a role of endothelin 1 and protein kinase C in nitroglycerin tolerance.

We sought to examine mechanisms responsible for increased vasoconstriction that occurs during development of nitroglycerin tolerance. Rabbits were treated for 3 days with nitroglycerin patches (0.4 mg/hr), and their aortic segments were studied in organ chambers. This treatment resulted in attenuated in vitro relaxations to nitroglycerin and increased contractile sensitivity to angiotensin II, serotonin, phenylephrine, KCl, and a direct activator of protein kinase C, the phorbol ester phorbol 12,13-dibutyrate. The protein kinase C antagonists calphostin C (100 nM) and staurosporine (10 nM) corrected the hypersensitivity to constrictors in tolerant vessels, yet had minimal effects on constrictions in control vessels. Paradoxically, constrictions caused by endothelin 1 were decreased in nitrate-tolerant vessels. Immunocytochemical analysis revealed intense endothelin 1-like and big endothelin 1-like immunoreactivity in the media of nitroglycerin-tolerant but not of control aortas. The enhanced vasoconstriction to angiotensin II, serotonin, KCl, and phenylephrine could be mimicked in normal vessels by addition of subthreshold concentrations of endothelin 1, and this effect was prevented by calphostin C. We propose that increased autocrine production of endothelin 1 in nitrate tolerance sensitizes vascular smooth muscle to a variety of vasoconstrictors through a protein kinase C-mediated mechanism.     

Tolerance to intravenous nitroglycerin in patients with congestive heart failure: role of increased intravascular volume, neurohumoral activation and lack of prevention with N-acetylcysteine

To better understand the mechanism of nitrate tolerance in patients with congestive heart failure, 13 patients received a 24 h infusion of nitroglycerin (1.5 micrograms/kg body weight per min) with or without N-acetylcysteine (225 mg/kg per 24 h). The infusions were separated by a 24 h nitrate-free interval. By the end of the nitroglycerin infusion, mean arterial pressure had returned to baseline values and there was a significant increase in ventricular filling pressures and systemic vascular resistance compared with values after 1 h of treatment. The simultaneous infusion of N-acetylcysteine had no effect on these changes. Although a strict fluid restriction of 1.5 liters/day was maintained for 1 week before and throughout the study, after 24 h of nitroglycerin infusion there was a significant and similar degree of hemodilution whether nitroglycerin was infused alone (9.1 +/- 4.3%) or with N-acetylcysteine (8.7 +/- 4.1%). This hemodilution corresponded to an increase in intravascular volume of 745 +/- 382 ml, most of which occurred during the 1st h. Plasma renin activity increased and plasma atrial natriuretic peptide decreased during the infusion. The results of this study suggest that nitrate tolerance is multifactorial. In addition to the previously described pharmacologic tolerance to the effect of nitroglycerin on vascular smooth muscle, a capillary fluid shift from the extravascular to intravascular space appears to be involved, especially during the 1st h of the infusion. A third mechanism, reflex neurohumoral activation, also seems to contribute to the genesis of nitroglycerin tolerance.     

Intravenous nitroglycerin infusion inhibits cyclic blood flow responses caused by periodic platelet thrombus formation in stenosed canine coronary arteries

BACKGROUND. Nitroglycerin and other clinically relevant organic nitrate derivatives have been shown to inhibit platelet aggregation in vitro. This antithrombotic effect of nitrates is potentiated by reduced thiol. To determine the potential relevance of this mechanism of action in vivo, we examined the effect of intravenous nitroglycerin infusion on periodic platelet thrombus formation in a canine model of coronary artery stenosis. METHODS AND RESULTS. We used a canine model of coronary artery stenosis associated with cyclic reductions in coronary blood flow that have been shown to depend on periodic platelet thrombus formation. We quantified the frequency of cycles per 40-minute observation period and monitored the effect of a continuous infusion of intravenous nitroglycerin on the cycle frequency. The administration of 10-15 micrograms/kg/min nitroglycerin reduced cyclic platelet thrombus formation significantly and did so without a significant change in coronary artery blood flow. Pretreatment with the reduced thiol, N-acetylcysteine (100 mg/kg during 30 minutes), led to inhibition of cyclic platelet thrombus formation by intravenous nitroglycerin at doses that alone had no such effect (5 micrograms/kg/min). CONCLUSION. These data suggest that one mechanism by which intravenous nitroglycerin improves ischemia in acute coronary artery disease syndromes may be by inhibition of platelet thrombus formation and may highlight the potential importance of reduced thiol in this mechanism.     

Comparison of the development of tolerance to nitroglycerin in aortic preparations isolated from non-diabetic and diabetic rats

Summary To clarify whether or not tolerance to nitroglycerin is developed more easily in a diabetic than in a non-diabetic state, the effects of nitroglycerin on aortic preparations isolated from diabetic and nondiabetic rats were examined and compared with those of nicorandil, which has been known to develop less tolerance than does nitroglycerin. Contractile responses to norepinephrine, relaxant responses to nitroglycerin and nicorandil, and the tolerance development to nitroglycerin were found to be no different between diabetic and non-diabetic aortic preparations. N-Acetylcysteine preincubated together with nitroglycerin prevented the tolerance development to nitroglycerin in non-diabetic but not in diabetic aortic preparations. The results suggest that the tolerance to nitroglycerin is developed in the diabetic as well as in the non-diabetic state.     

激活乙醛脱氢酶2抑制硝酸甘油耐受大鼠缺血再灌注心肌损伤

目的:探讨乙醛脱氢酶2（ALDH2）激动剂（Alda-1）对硝酸甘油耐受(NT)大鼠心肌缺血/再灌注损伤(MI/RI)的影响。方法: 24只成年雄性SD大鼠随机分为4组:Con组、Alda-1组、NT组和NT+Alda-1治疗组，每组6只(n=6)。经静脉给予硝酸甘油10 mg/(kg·day)处理7 d，建立NT大鼠模型，治疗组在硝酸甘油给药的第5天起，同时输注Alda-110 mg/(kg·day) 3 d。模型建立后，采用冠脉左前降支结扎缺血30 min再灌注4 h建立在体大鼠急性心肌缺血/再灌注(MI/R)模型。术中监测血流动力学指标，再灌结束后检测血清乳酸脱氢酶(LDH)并取心肌组织检测心肌梗死面积、蛋白质羰基化程度和心肌内活性氧簇(ROS)的水平。结果: 离体血管灌流显示，硝酸甘油连续处理7 d，可导致大鼠血管内皮依赖性和内皮非依赖性舒张能力显著降低，提示出现NT。定量检测心肌ALDH2的活性发现Alda-1可显著改善NT导致的心肌ALDH2活性抑制。在NT情况下，MI/RI较对照组显著加重，表现为心肌收缩舒张速率显著降低，血清LDH的水平显著增加，心肌梗死面积扩大（均P<0.05）。与NT组相比，采用Alda-1治疗，可显著改善NT组大鼠的MI/RI（均P<0.05）。并且，Alda-1治疗可显著抑制NT情况下缺血/再灌注心肌中蛋白质羰基化程度和ROS的含量。结论: 激活ALDH2可显著抑制NT导致的MI/RI加重，其机制可能与减轻心肌蛋白质氧化损伤有关。     

Mechanisms of interaction between the sulfhydryl precursor L-methionine and glyceryl trinitrate.

BACKGROUND. L-Methionine potentiates systemic hemodynamic effects of intravenous glyceryl trinitrate (GTN) in tolerant and nontolerant patients to a similar extent as N-acetylcysteine (NAC). This potentiation of GTN action by L-methionine has been attributed to enhanced intracellular formation of nitrosothiols, known to be potent stimulators of soluble guanylyl cyclase. This study was performed to analyze directly the effects of L-methionine on GTN-induced dilation of large epicardial arteries and the venous capacitance system of the dog in the tolerant and nontolerant states. Cultured rat aortic vascular smooth muscle cells and purified guanylyl cyclase were used to study potential intracellular and extracellular mechanisms responsible for this interaction. METHODS AND RESULTS. In awake nontolerant dogs, L-methionine (100 mg/kg) potentiated the tachycardic response to GTN (5.0 and 15 micrograms/kg/min) and enhanced the hypotensive action of GTN (1.5 and 5.0 micrograms/kg/min) in anesthetized, nonreflexic dogs. In nontolerant and tolerant dogs, however, L-methionine did not alter the dose-response of large epicardial artery dilation to intravenous GTN challenges and did not modify nitrate tolerance of the low pressure system of the dog. The infusion of L-methionine (100 mg/kg) significantly increased plasma methionine levels (from 52 +/- 12 to 1,141 +/- 239 microM), cystine levels (from 12 +/- 4 to 26 +/- 7 microM), but not homocystine levels. In vitro, the L-methionine conversion product L-cysteine (0.1-1.0 mM) but not homocysteine significantly enhanced the augmentation of purified guanylyl cyclase activity by GTN (100 microM). Incubation of cultured rat aortic smooth muscle cells with L-methionine (10 microM or 1 mM) did not result in a significant increase of free intracellular sulfhydryl group content. CONCLUSIONS. The L-methionine conversion product L-cysteine mediates tolerance independent the potentiation of GTN action. This may result from an L-cysteine-induced formation of a vasoactive metabolite of GTN (nitric oxide) or nitrosothiol. This effect occurs primarily in the resistance vessel circulation, not in large epicardial arteries and veins. The lack of effect of L-methionine on sulfhydryl group content in large conductance vessels indicates that hepatic L-methionine metabolism constitutes the significant source of L-cysteine. These findings strongly suggest that administration of sulfhydryl-group precursor L-methionine does not represent a therapeutic alternative to a nitrate-free interval to restore nitrate sensitivity in tolerant large epicardial arteries and veins.     

不同剂量硝酸甘油对妊娠大鼠血压的影响

目的 硝酸甘油作为一种一氧化氮（NO）的供体,已被应用于产科临床。本文探讨不同剂量硝酸甘油对妊娠大鼠血压变化的影响。方法 妊娠7－17天之SD大鼠,每日一次口腔滴予硝酸甘油混悬液,剂量分别为0．025mg/kg体重、0.85mg/kg体重、8.5mg/kg体重,生理盐水对照。同样设未妊娠大鼠各剂量组。给药后30min、60min、120min用尾套法测定血压。结果 给药后30min各组血压下降,妊娠组降低幅度较大,低剂量组60min血压回升,而两高剂量组血压回升缓慢。结论 应用常规较低剂量硝酸甘油对孕母血压的影响在安全范围,不会导致母体血压过度、持续低值而影响胎盘灌注量和胎儿血供。     

The hydroxyl radical scavengers dimethylsulfoxide and dimethylthiourea protect rats against thioacetamide-induced fulminant hepatic failure.

BACKGROUND/AIMS: Reactive oxygen species, proinflammatory cytokines, glutathione depletion and nitric oxide have all been implicated in the pathogenesis of fulminant hepatic failure. The aim of the present study was to examine the respective roles of these factors in the pathogenesis of thioacetamide-induced fulminant hepatic failure in rats. METHODS: Fulminant hepatic failure was induced by 3 consecutive intraperitoneal injections of thioacetamide (400 mg/kg) at 24-h intervals. Rats were pretreated with one of the following agents: the free radical scavengers dimethylsulfoxide (4 g/kg every 6 h) or dimethylthiourea (200 mg/kg every 12 h), the glutathione donor, N-acetylcysteine (130 or 200 mg/kg every 6 h), or the anti-tumor necrosis factor-alpha agents pentoxifylline (100 and 200 mg/kg) and soluble tumor necrosis factor receptor (100 or 1000 microg/rat). The nitric oxide synthase inhibitor N-mono-methyl arginine ester (L-NAME, 0.1 mg/ml) was administered in the drinking water, starting 7 days prior to thioacetamide administration. RESULTS: Serum levels of liver enzymes, blood ammonia and prothrombin time and the stage of hepatic encephalopathy were significantly improved in rats treated with dimethylsulfoxide or dimethylthiourea compared to the other treatment groups (p<0.001). Liver histology and the survival rate in these rats were not adversely affected by thioacetamide administration (p<0.001), while in all the other treatment groups those parameters were similar to control rats with fulminant hepatic failure. Furthermore, dimethylsulfoxide ameliorated liver damage and improved survival even when its administration was initiated 8 and 16 h after the first thioacetamide injection. The hepatic concentration of methanesulfinic acid, which is produced after direct interaction of dimethylsulfoxide with hydroxyl radicals, was increased five-fold in rats treated with thioacetamide+dimethylsulfoxide (p<0.001), suggesting a role for hydroxyl radical scavenging in the protection from fulminant hepatic failure in this model. In the group of thioacetamide-treated rats that were pretreated with L-NAME, liver enzymes, blood ammonia levels and the mortality rate were higher than in the control group, treated with thioacetamide only. CONCLUSIONS: In thioacetamide-induced fulminant hepatic failure, the hydroxyl radical scavengers dimethylsulfoxide and dimethylthiourea prevent liver injury. Neither N-acetylcysteine nor antagonists of tumor necrosis factor-alpha are protective in this rat model. Inhibition of nitric oxide formation aggravates liver damage and reduces the survival of rats with thioacetamide-induced liver damage.     

Protective action of a calcium antagonist, nilvadipine, against aortic calcium deposition--a pathogenic factor in atherosclerosis

Nilvadipine and other calcium antagonists were studied for their effect on 1-alpha-hydroxyvitamin D3 (1 - alpha (OH)D3)-induced aortic calcium deposition in rats. The animals were treated orally with 1-alpha (OH)D3 (10 micrograms/kg) for 2 weeks. Calcium antagonists were given orally twice a day during the same period. The aortic calcium content in 1-alpha (OH)D3-treated rats increased to about 100 times that in the control. Nilvadipine reduced the aortic calcium deposition dose-dependently, with percent inhibition of 6, 43, 72 and 92%, at doses of 0.1, 1, 10 and 100 mg/kg, respectively. Similar activities were obtained for the other calcium antagonists except diltiazem which had no effect even at the largest dose of 100 mg/kg. According to the ED50 values, nilvadipine (2.2 mg/kg) was more potent than nifedipine (23.2 mg/kg), nicardipine (12.4 mg/kg) and verapamil (32.0 mg/kg). Scanning and transmission electron microscopy showed clear-cut degenerative changes in the endothelial cells after 1-alpha (OH)D3 treatment. Nilvadipine exerted a protective effect against these degenerative changes but not against 1-alpha (OH)D3-induced hypercalcemia. Furthermore, the drug had only minimal effect on in vitro calcification of the aorta. Our findings suggest that nilvadipine inhibits aortic calcification by protecting the aortic wall cells.     

Concurrent hydralazine administration prevents nitroglycerin-induced hemodynamic tolerance in experimental heart failure

BACKGROUND. Organic nitrates such as nitroglycerin and isosorbide dinitrate are useful in the treatment of congestive heart failure (CHF), but tolerance develops rapidly during continuous administration. Because combination therapy of nitrate and hydralazine has been shown to provide both short- and long-term benefit but nitrate alone produces hemodynamic tolerance, we questioned whether hydralazine can preserve the favorable preload effects of nitroglycerin. METHODS AND RESULTS. Using an in vivo model of nitroglycerin tolerance in the CHF rat, we examined the effects of hydralazine bolus dosing during continuous nitroglycerin infusion. Continuous infusion of nitroglycerin alone (10 micrograms/min) produced initial reductions in left ventricular end-diastolic pressure of 40-50%, which returned to baseline by 8 hours (tolerance development). Coadministration of hydralazine (2 x 0.1 mg) maintained the effects of nitroglycerin infusion on left ventricular end-diastolic pressure (45% reduction at 10 hours). This hydralazine dose alone reduced left ventricular peak systolic pressure by approximately 12 +/- 3% but had no effect on left ventricular end-diastolic pressure. Hydralazine dosing did not affect steady-state plasma concentrations of nitroglycerin or metabolites, and hydralazine was unable to prevent nitroglycerin tolerance induced in vitro. CONCLUSIONS. The beneficial interaction of hydralazine on the preload effects of nitroglycerin may explain the long-term clinical efficacy of hydralazine/nitrate combination in CHF. Our results also suggest that the mechanism of in vivo nitrate tolerance in CHF may be systemic rather than vascular in origin.     

大剂量硝酸甘油对大鼠母、胎心血管的影响

目的:通过研究超大剂量硝酸甘油对大鼠母体、胎儿心血管组织诱生型一氧化氮合酶(iNOS)产生的影响,探讨其组织安全性。方法:给妊娠第7～17天之孕鼠口腔滴入硝酸甘油混悬液,每日1次,剂量分别为0.25 mg/kg体重、0.85 mg/lg体重,8.5mg/kg体重;另给生理盐水作为对照,4组每组15只鼠。妊娠足月后,分别取母、儿心脏、升主动脉,采用兔抗入iNOS单克隆抗体,免疫组织化学ABC法检测组织中iNOS的表达。结果;低剂量组(A组)及对照组母、儿心脏、大血管均未见iNOS染色.0.85 mg/kg体重组(B组)个别母鼠心脏内膜下肌层有iNOS表达,母鼠血管及仔鼠心脏、血管均未见iNOS表达,8.5mg/kg体重组(C组)母鼠心肌、血管平滑肌iNOS表达显著多于B组(P<0.05),仔鼠心脏、血管未见iNOS表达。结论:常规低剂量使用硝酸甘油对妊娠母体、胎儿心血管是安全的,而超量硝酸酸甘油在组织内可释放超量NO,发挥细胞毒作用.诱导iNOS表达,进一步引起细胞、组织的损伤。     

肾上腺髓质素对大鼠血管钙化的影响

目的　观察肾上腺髓质素 (ADM)对血管钙化的影响。方法　维生素D3 (VitD3 )和尼古丁制备大鼠血管钙化模型 ,分别测定血管、心肌钙含量和血管碱性磷酸酶 (ALP)活性 ,血浆和血管ADM含量 ,12 5I ADM与ADM受体的结合力及血管环磷酸腺苷 (cAMP)含量。结果　与对照组相比 ,钙化组 (VDN组 )的血管钙含量和ALP活性明显升高 ;血管及血浆ADM的含量亦升高 ,但12 5I ADM与血管质膜ADM受体结合的位点减少 ,Kd值升高 ,提示亲合力降低 ,同时伴钙化血管的cAMP合成减少。提示钙化血管对ADM的反应减弱。空载脂质体对血管钙化无影响。用脂质体包裹ADM组 (VDN ADM组 )与钙化组相比 ,其血管的钙含量、ALP的活性均明显降低 ;12 5　I ADM与血管质膜ADM受体结合的位点增加 ,Kd值减少 ,cAMP的合成也增加 ,提示该组血管对ADM的反应增强。结论　血管钙化时ADM ADM受体 cAMP途径发生变化 ,外源性ADM通过改善ADM ADM受体 cAMP途径 ,发挥抑制血管钙化的作用     

Reduced thiols and the effect of intravenous nitroglycerin on platelet aggregation

Nitroglycerin inhibits platelet aggregation in vitro and this effect may be important in its overall mechanism of action. In addition, its use has been associated with prolonged bleeding times and hemorrhagic complications. Despite these experimental and clinical observations, no significant antiplatelet effect of nitroglycerin has been observed ex vivo during intravenous nitroglycerin administration to patients. Because the in vitro antiplatelet effects of nitroglycerin have been shown by one of the investigators participating in this study to depend on the presence of sufficient stores of reduced intracellular thiol--which are readily depleted ex vivo by nitroglycerin in the formation of S-nitrosothiols--an attempt was made to unmask nitroglycerin-mediated inhibition of platelet aggregation by exposing platelets taken from patients treated with nitroglycerin to the reduced thiol N-acetylcysteine ex vivo. The obtained data demonstrate that platelets taken from patients treated with intravenous nitroglycerin manifest attenuated aggregation responses ex vivo when thiol stores are repleted. It is therefore proposed that the mechanism of action of nitroglycerin is mediated in part by its antiplatelet effect and that this effect depends on the adequacy of reduced intracellular thiol stores.     

N-acetylcysteine and glycyrrhizin combination: Benefit outcome in a murine model of acetaminophen-induced liver failure

BACKGROUND Acetaminophen overdose is the most frequent cause of drug-induced liver failure in developed countries. Substantial progress has been made in understanding the mechanism of hepatocellular injury, but N-acetylcysteine remains the only effective treatment despite its short therapeutic window. Thus, other hepatoprotective drugs are needed for the delayed treatment of acetaminopheninduced hepatotoxicity. Our interest focused on glycyrrhizin for its role as an inhibitor of high mobility group box 1(HMGB1) protein, a member of the family of damage-associated molecular pattern, known to play an important pathological role in various diseases.AIM To investigate the efficacy of the N-acetylcysteine/glycyrrhizin combination compared to N-acetylcysteine alone in the prevention of liver toxicity.METHODSEight-week-old C57 BL/6 J wild-type female mice were used for all our experiments. Mice fasted for 15 h were treated with acetaminophen(500 mg/kg) or vehicle(phosphate-buffered saline) by intraperitoneal injection and separated into the following groups: Glycyrrhizin(200 mg/kg); N-acetylcysteine(150 mg/kg); and N-acetylcysteine/glycyrrhizin. In all groups, mice were sacrificed 12 h following acetaminophen administration. The assessment of hepatotoxicity was performed by measuring plasma levels of alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase. Hepatotoxicity was also evaluated by histological examination of hematoxylin and eosin-stained tissues sections. Survival rates were compared between various groups using Kaplan-Meier curves.RESULTS Consistent with data published in the literature, we confirmed that intraperitoneal administration of acetaminophen(500 mg/kg) in mice induced severe liver injury as evidenced by increases in alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase but also by liver necrosis score. Glycyrrhizin administration was shown to reduce the release of HMGB1 and significantly decreased the severity of liver injury. Thus, the co-administration of glycyrrhizin and N-acetylcysteine was investigated. Administered concomitantly with acetaminophen, the combination significantly reduced the severity of liver injury. Delayed administration of the combination of drugs, 2 h or 6 h after acetaminophen, also induced a significant decrease in hepatocyte necrosis compared to mice treated with N-acetylcysteine alone. In addition, administration of N-acetylcysteine/glycyrrhizin combination was associated with an improved survival rate compared to mice treated with only N-acetylcysteine.CONCLUSION We demonstrate that, compared to N-acetylcysteine alone, co-administration of glycyrrhizin decreases the liver necrosis score and improves survival in a murine model of acetaminophen-induced liver injury. Our study opens a potential new therapeutic pathway in the prevention of acetaminophen hepatotoxicity.     

Nitrate tolerance: the lack of effect of N-acetylcysteine

The hemodynamic and antianginal effects of 30 mg of isosorbide dinitrate (ISDN) were assessed in 12 patients with chronic stable angina after initial dosing and after 7 to 10 days of therapy four times daily. During early therapy, ISDN produced significant hemodynamic and antianginal effects that persisted over a 3 hr observation period. During sustained therapy there was attenuation of the hemodynamic effects at rest, and treadmill exercise time to the onset of angina and to the development of moderate angina was increased 1 hr after dosing; no effect was apparent at 3 hr. During this state of nitrate tolerance, patients were treated with an infusion of normal saline or 100 mg/kg N-acetylcysteine and exercise testing was repeated. N-Acetylcysteine did not change the hemodynamic findings at rest or during exercise and there was no improvement in exercise tolerance. It is apparent that the short-term administration of reduced sulfhydryl groups does not reverse tolerance to the hemodynamic and antianginal effects of isosorbide dinitrate in an exercise test model.     

Effect of Transdermal Nitroglycerin or N-Acetylcysteine,or Both,in the Long-Term Treatment of Unstable Angina Pectoris

Objectives. This study was designed to evaluate whether the addition of transdermal nitroglycerin or oral N-acetylcysteine, or both, to conventional medical therapy improves the natural history of unstable angina pectoris.Background. Transdermal nitroglycerin is widely used to treat angina pectoris, but the development of tolerance is a major problem that may reduce its clinical efficacy. It has been suggested that the addition of N-acetylcysteine to nitroglycerin reverses the development of tolerance, potentiates the hemodynamic response to nitroglycerin and may improve in-hospital prognosis in unstable angina.Methods. We assessed the efficacy of adding transdermal nitroglycerin or oral N-acetylcysteine, or both, to conventional medical therapy in a randomized, double-blind, placebo-controlled trial involving 200 patients with unstable angina who were followed up for 4 months.Results. Outcome events—death, myocardial infarction or refractory angina requiring revascularization—occurred in 31% of patients receiving nitroglycerin, 42% of those receiving N-acetylcysteine, 13% of those receiving nitroglycerin plus N-acetylcysteine and 39% of those receiving placebo (p = 0.0052). Kaplan-Meier curves showed a higher probability (p < 0.01) of no failure of medical treatment in the group receiving both nitroglycerin and N-acetylcysteine than in those receiving placebo, N-acetylcysteine or nitroglycerin alone. The combination of nitroglycerin and N-acetylcysteine was associated with a high incidence of side effects (35%), mainly intolerable headache, which was almost twice as frequent as in patients receiving nitroglycerin alone.Conclusions. The combination of nitroglycerin and N-acetylcysteine, associated with conventional medical therapy in the long-term treatment of patients with unstable angina, reduces the occurrence of outcome events. However, the high incidence of side effects limits the clinical applicability of this therapeutic strategy at least at the dosage used in the present study.(J Am Coll Cardiol 1997;29:941–7)© 1997 by the American College of Cardiology     

Antidiabetic actions of arachidonic acid and zinc in genetically diabetic Goto-Kakizaki rats

In previous studies, we showed that feeding arachidonic acid (AA) supplemented with a fixed amount of zinc lowered blood glucose concentrations in the fed state and water intake in rats with streptozotocin-induced diabetes. The present study was designed to determine dose-dependent effects of AA supplemented with a fixed amount of zinc on fed blood glucose levels, water intake, and glucose tolerance in genetically type 2 diabetic Goto-Kakizaki (G-K) Wistar rats. In an acute study, 20 mg/kg AA plus 10 mg/kg zinc administered via gastric gavage significantly improved oral glucose tolerance in G-K rats when compared to rats given distilled water (DW) only. When rats were treated chronically (2 weeks) with increasing doses of AA in drinking water, fed blood glucose concentrations and water intake were maximally decreased with diets containing 20 or 30 mg/L AA plus 10 mg/L zinc. Three-hour average area-above-fasting glucose concentrations (TAFGC; index of oral glucose tolerance) in diabetic G-K rats treated with 10, 20, or 30 mg/L AA plus 10 mg/L zinc for 2 weeks were significantly decreased relative to DW-treated rats. The effect on TAFGC values was maintained for an additional 2 weeks after cessation of treatment. Plasma insulin levels significantly increased in rats treated with 20 mg/L AA only or 10 mg/L AA plus 10 mg/L zinc, but not in rats treated with 20 or 30 mg/L AA plus 10 mg/L zinc, which are the most effective doses for the improvement of clinical signs of diabetes in G-K rats. In in vitro assays, 0.2 mg/mL AA in the incubation media was optimal for glucose uptake in isolated soleus muscle slices. These results suggest that treatment of genetically diabetic G-K rats with AA plus zinc lowers blood glucose levels via improvement of insulin sensitivity.     

Selective Effect of High Arterial Pressure in Hypertension Upon Inhibition of cGMP Versus cAMP Mediated Vascular Relaxation

We tested the hypothesis as to whether elevated arterial pressure in hypertension alters cGMP, or cAMP, mediated vasorelaxation. Relaxation to nitroglycerin and isoproterenol was determined in isolated aortic rings from one-kidney, one clip hypertensive (1K1C), coarctation hypertensive (CH) and normotensive control (C) rats. Thoracic aortas from 1K1C and CH rats, as well as abdominal aortas from 1K1C rats, but not abdominal aortas from CH rats were exposed chronically (4–6 weeks) to elevated arterial pressure. Sensitivity of rings with and without endothelium to nitroglycerin was suppressed significantly only in vessels exposed chronically to high arterial pressure. Impaired sensitivity to nitroglycerin in abdominal rings from lKlC rats could not be abolished by exposure to 100 uM L-arginine, the substrate for production of NO by endothelial nitric oxide synthase, or 100 uM L-cysteine, the source of thiol groups required for the production of nitric oxide from nitroglycerin. Maximum relaxation to isoproterenol was impaired significantly in thoracic and abdominal rings, with and without endothelium, from lKlC and CH rats. Relaxation to 8-bromo-cGMP and dibutyryl cAMP was similar in abdominal rings from all groups. We conclude that impaired vasorelaxation to nitroglycerin and isoproterenol in hypertension involves mechanisms prior to activation of vascular smooth muscle cGMP-dependent and cAMP dependent protein kinase, respectively. Impaired cGMP, but not cAMP, mediated relaxation of aortas appears to result from their exposure to high arterial pressure per se. This effect does not appear to involve the vascular endothelium or vascular sources of thiols, but rather may reflect an effect of high arterial pressure to impair the ability of the artery to respond t o nitric oxide derived from nitroglycerin.