Bernard Dupuis

Long-term oral administration of L-arginine reduces intimal thickening and enhances neoendothelium-dependent acetylcholine-induced relaxation after arterial injury

BackgroundNitric oxide (NO), in addition to its potent vasorelaxant properties, may participate in growth regulation of cultured smooth muscle cells. It was recently demonstrated that in vivo endothelial injury induces the production of NO from L-arginine in the arterial wall. Methods and ResultsWe studied the effects of long-term administration of L-arginine, the precursor of NO, on neointimal thickening and on neoendothelium-dependent vasorelaxation 4 weeks after balloon denudation of normocholesterolemic rabbit iliac arteries. Rabbits were fed with either a standard diet or a diet supplemented with L-arginine (2.25%) in their drinking water 3 days before and during 4 weeks after balloon denudation. The effectiveness of L-arginine supplementation was confirmed by measurement of plasma arginine levels. L-Arginine had no effect on hemodynamic parameters. All animals were killed 4 weeks after balloon denudation, and a digital histomorphometric analysis of three serial nonconsecutive histological cross sections per iliac artery was performed. Intimal thickening was reduced (P<.05) from 0.43±0.08 (SE) mm2 in controls (n=8) to 0.24±0.02 mm2 in treated animals (n=8). Ten animals (n=5 in each group) were used for in vitro vasoreactivity assessment 4 weeks after balloon denudation. Neoendotheliumdependent acetylcholine-induced relaxation (10−8 mol/L to 3.10−5 mol/L) in treated animals (Emax=−24.1±5.5%) was significantly greater than in controls (Emax=−8.9±2.2%). Endothelium- independent relaxation did not differ between groups (Emax= −58.1±6.5% in L-argimine-supplemented animals versus −52.9±6.8% in controls). ConclusionsOur results demonstrate that L-arginine, a precursor of NO, reduces neointimal thickening after balloon denudation and improves neoendothelial-dependent acetylcholine- induced relaxation.

Increase in endogenous brain superoxide dismutase as a potential mechanism of lipopolysaccharide-induced brain ischemic tolerance.

A low dose (0.5 mg/kg) of lipopolysaccharide (LPS), administered 72 hours before 60-minute middle cerebral artery occlusion, induced a delayed neuroprotection proven by the significant decrease (–35%) of brain infarct volume in comparison with control, whereas infarct volumes remained unchanged in rats treated 12, 24, or 168 hours before ischemia. This delayed neuroprotective effect of LPS was induced only with low doses (0.25 to 1 mg/kg), whereas this effect disappeared with a higher dose (2 mg/kg). The delayed neuroprotection of LPS was induced in the cortical part of the infarcted zone, not in the subcortical part. The beneficial effect of LPS on consequences of middle cerebral artery occlusion was suppressed by dexamethasone (3 mg/kg) and indomethacin (3 mg/kg) administered 1 hour before LPS, whereas both drugs had no direct effect on infarct volume by themselves, suggesting that activation of inflammatory pathway is involved in the development of LPS-induced brain ischemic tolerance. Preadministration of cycloheximide, an inhibitor of protein synthesis, also blocked LPS-induced brain ischemic tolerance suggesting that a protein synthesis is also necessary as a mediating mechanism. Superoxide dismutase (SOD) could be one of the synthesized proteins because lipopolysaccharide increased SOD brain activity 72 hours, but not 12 hours, after its administration, which paralleled the development of brain ischemic tolerance. In contrast, catalase brain activity remained unchanged after LPS administration. The LPS-induced delayed increase in SOD brain content was suppressed by a previous administration of indomethacin. These data suggest that the delayed neuroprotective effect of low doses of LPS is mediated by an increased synthesis of brain SOD that could be triggered by activation of inflammatory pathway.

Prognostic value of the dobutamine test in patients with sepsis syndrome and normal lactate values: a prospective, multicenter study.

To determine the oxygen supply (Vo2) and uptake (Vo2) responses to a 60-min dobutamine infusion in critically ill septic patients without circulatory shock and with normal blood lactate concentrations. Also, to determine whether these responses would predict outcome. Design:Prospective, cohort study. Setting:Five intensive care units in university-affiliated, city hospitals. Patients:Fifty critically ill patients with sepsis syndrome were studied from April 1990 to August 1991. Interventions:Pulmonary artery catheteriza-tion; fluid loading if pulmonary artery occlusion pressure was <10 mm Hg; and 10 μg/min/kg dobutamine infusion for 60 mins. Measurements and Main Results:Cardiac in-dex, Vo2, Vo2, and oxygen extraction ratio were determined immediately before and 1 hr after the onset of the dobutamine test. Using receiver operating characteristic curves, responders to the dobutamine infusion were identified by a >15% increase in Vo2 from the time immediately before to 1 hr after the onset of the dobutamine test. We identified 23 responders and 27 nonresponders. Groups differed significantly in age (responders 46 yrs vs. nonresponders 55 yrs) and associated chronic disease (responders one cancer vs. nonresponders six cancers). Significant changes in responders were: a) cardiac index increased 42.9%; b) systemic vascular resistance decreased 20.7%; and c) Vo2 increased 39.1% while Vo2 increased 40.8%, with no changes in oxygen extraction or blood lactate concentration. Significant changes in nonresponders were: a) cardiac index increased 14.2%; b) Vo2 increased 13.2%; and c) oxygen extraction decreased from 0.26 to 0.22. Lactate concentration increased significantly by 25.1% in nonresponders. The mortality rate in responders (8.7%) was significantly less than that rate in nonresponders (44.4%). Conclusions:Most of these septic patients without shock or hyperlactatemia responded to dobutamine infusion in one of two ways: with little increase in Vo2 and no increase in Vo2, or with significant increases in both Vo2 and Vo2 The latter response is typical of healthy volunteers given dobutamine. Because of the calorigenic effect of dobutamine, our results imply nothing about the presence or absence of oxygen supply limitation. Still, patients who had increases in Vo2 and Vo2 had a much higher survival rate than patients who did not. We speculate that the inability of some patients to respond to dobutamine and the associated higher mortality rate may be related to β-adrenoreceptor dysfunction. (Crit Care Med 1993; 21:1868–1875)

Cisapride‐induced prolongation of cardiac action potential and early afterdepolarizations in rabbit Purkinje fibres

Cisapride, a gastrointestinal prokinetic agent, has been associated with cases of Torsades de Pointes but its effects on the cardiac action potential have not been described. We investigated its electrophysiological effects on rabbit isolated Purkinje fibres. The results demonstrated that cisapride (0.01 ×10 μm) lengthened concentration‐dependently the action potential duration without modifying other parameters and induced early after depolarizations and subsequent triggered activity. This typical class III antiarrhythmic effect, that showed ‘reverse’ rate‐dependence and was reduced by increasing external K concentration, can account for clinical arrhythmogenesis.

Dobutamine improves gastrointestinal mucosal blood flow in a porcine model of endotoxic shock.

OBJECTIVE To test the hypothesis that saline solution plus dobutamine increases gastrointestinal mucosal perfusion better than saline solution alone in a model of endotoxic shock. DESIGN Prospective, randomized, unblinded study. SETTING Animal research laboratory affiliated with a university teaching hospital. SUBJECTS Twelve female pigs, weighing 30 to 32 kg. INTERVENTIONS Animals were anesthetized, and their lungs were mechanically ventilated. Catheters were inserted into the right atrium, pulmonary artery, and carotid artery for blood sampling and blood pressure and cardiac output measurements. A tonometer and a laser Doppler probe were placed in the lumen of the stomach and the ileum for determination of mucosal acid-base status and measurement of mucosal blood flow. Group 1 animals (n = 6) received an infusion (T = 0 min) of 150 mcirog/kg Escherichia coli endotoxin and normal saline solution (0.3 mL/kg/min). Group 2 animals (n = 6) received an infusion of endotoxin and were resuscitated with the same method as used in group 1, but an infusion of dobutamine (5 microg/kg/min) was begun at T = 60 mins, and continued for the duration of the experiment. MEASUREMENTS AND MAIN RESULTS Both experimental regimens produced shock, with decreased mean arterial pressure and systemic vascular resistance, without change in cardiac output and oxygen delivery. Endotoxin plus saline infusion decreased gastrointestinal mucosal blood flow to <60% of baseline and decreased gastrointestinal pH. In contrast, gastrointestinal mucosal blood flow returned to baseline values, and intramucosal pH tended to normalize by the end of the saline solution plus dobutamine resuscitative protocol. CONCLUSION Compared with saline solution alone, saline solution plus dobutamine increased blood flow to the gastrointestinal mucosa, and may have partially improved oxygenation.

Role of Nitric Oxide in Restenosis After Experimental Balloon Angioplasty in the Hypercholesterolemic Rabbit: Effects on Neointimal Hyperplasia and Vascular Remodeling

OBJECTIVES The purpose of this study was to assess the effects of L-arginine and N(G)-nitro-L-arginine methyl ester (L-NAME) on neointimal hyperplasia and vascular remodeling after balloon angioplasty in the hypercholesterolemic rabbit. BACKGROUND Restenosis after balloon angioplasty is a consequence of both neointimal hyperplasia and vessel remodeling. Nitric oxide inhibits neointimal hyperplasia, but its effect on vessel remodeling is unknown. METHODS Six weeks after induction of bilateral iliac atherosclerosis, 48 rabbits underwent successful angioplasty in 75 vessels. Eight rabbits (acute group) were sacrificed immediately after angioplasty. The remaining animals received either placebo (chronic control group), or a diet supplemented with either L-arginine (1.5 g/kg/day), or L-NAME (15 mg/kg/day) for 4 weeks after angioplasty. RESULTS The intimal area was significantly greater in the chronic control group compared to the acute group (2.60+/-1.03 mm2 vs. 1.35+/-0.62 mm2). This increase in intimal area was lower in the L-arginine group (1.79+/-0.61 mm2), and greater in the L-NAME group (3.23+/-0.92 mm2). The area circumscribed by the internal elastic lamina (IEL) increased significantly in the control group compared to the acute group (from 2.52+/-0.66 to 3.33+/-0.85 mm2); a more marked increase occurred in the L-NAME group (3.90+/-0.85 mm2). By contrast, IEL area was unchanged in the L-arginine group (2.41+/-0.62 mm2). As a result, there was no significant difference in lumen area after 4 weeks in the chronic groups (control: 0.74+/-0.38 mm2; L-arginine: 0.50+/-0.43 mm2; L-NAME: 0.48+/-0.42 mm2). CONCLUSIONS Our results demonstrate that L-arginine inhibits whereas L-NAME stimulates neointimal hyperplasia after experimental balloon angioplasty in the hypercholesterolemic rabbit. However, the lack of vessel enlargement in the L-arginine group resulted in a similar final lumen size in the L-NAME and L-arginine groups.

Detrimental effect of propranolol in patients with coronary arterial spasm countered by combination with diltiazem

This study determines, with quantitative variables, if propranolol is detrimental in patients with documented coronary arterial spasm and if this drug can be used in combination with calcium antagonists. Eleven patients with documented coronary spasm were entered prospectively in a study with 4 phases of 2 days each: (1) control, (2) diltiazem or propranolol (mean 225 +/- 75 mg/day), (3) propranolol or diltiazem (360 mg/day), (4) propranolol and diltiazem. The effects of the drugs were assessed by the detection of ischemic electrocardiographic episodes (24-hour electrocardiographic monitoring) and provocative tests with ergonovine. During the period of treatment with propranolol, the number and the duration of attacks increased and provocative tests had positive results in all patients. Diltiazem completely abolished spontaneous episodes, but 6 of 11 patients remained sensitive to the administration of ergonovine. The association of the 2 drugs led to a disappearance of ischemic episodes. In conclusion, propranolol is ineffective in patients with coronary artery spasm. It can be used in combination with diltiazem, but without any advantage over diltiazem alone.

Neointimal thickening after balloon denudation is enhanced by aldosterone and inhibited by spironolactone, and aldosterone antagonist

OBJECTIVE The aim was to examine the effects of aldosterone and of an aldosterone antagonist, spironolactone, on neointimal thickening in a rabbit model of balloon injury. METHODS Eighteen rabbits underwent aortic and iliac balloon injury and were randomised to subcutaneous infusion of aldosterone (70 micrograms.kg-1.d-1) or vehicle solution for 28 d. Eighteen other rabbits were randomised to receive daily subcutaneous injections of spironolactone (50 mg.kg-1.d-1) or of vehicle for 7 d before injury and for 28 d after the procedure. All animals were then killed just after measurement of plasma renin activity and of arterial pressure. Vessels were fixed and five cross sections were analysed per rabbit (three aortic; two from iliac artery). Mean values of neointimal area and of the neointimal area/medial area ratio were calculated. RESULTS Aldosterone treatment was associated with a decrease in renin activity and a non-significant increase in mean arterial pressure. Aldosterone significantly augmented the neointimal thickening in the iliac artery [0.42(SEM 0.07) v 0.24(0.03) mm2, P < 0.05] but not in the aorta [0.63(0.08) v 0.59(0.12) mm2, NS]. Spironolactone significantly inhibited intimal thickening, both in the iliac artery [0.09(0.02) v 0.29(0.01) mm2, P < 0.001] and in the aorta [0.31(0.03) v 0.59(0.06) mm2, P < 0.001]. Spironolactone administration was associated with an increase in renin activity and a decrease in mean arterial blood pressure. CONCLUSIONS Aldosterone administration enhances neointimal thickening after injury and spironolactone, an aldosterone antagonist, is a potent inhibitor of neointimal thickening in the same model. This suggests a role for aldosterone in the pathophysiology of neointimal proliferation after balloon injury and for aldosterone antagonists in its prevention.

The association between the neuroleptic malignant syndrome and malignant hyperthermia

The neuroleptic malignant syndrome (NMS) is an uncommon but dangerous complication of treatment with neuroleptic drugs. A primary defect in skeletal muscle has been suggested in view of similarities in the clinical presentations of NMS and anaesthetic‐induced malignant hyperthermia (MH). The in vitro halothanecaffeine contracture tests are the most reliable method of identifying individuals susceptible to MH. The aim of this study was to define if a relationship exists between NMS and MH susceptibility. Hence, the in vitro halothane and caffeine contracture tests were performed on muscle tissue obtained from eight NMS, ten MH‐susceptible and ten control patients. The results, which are expressed in accordance with the criteria of the European MH Group, defined the eight NMS subjects as MH non‐susceptible. The response to halothane and caffeine exposure of skeletal muscle from NMS and control subjects was the same and significantly different from that of muscle from patients susceptible to MH. Furthermore, muscle from subjects in NMS and control group responded similarly to increasing concentrations of chlorpromazine. These results do not point towards an association between NMS and MH.

Relationship between Inward Rectifier Potassium Current Impairment and Brain Injury after Cerebral Ischemia/Reperfusion

Functional alterations of barium-sensitive potassium inward rectifier (Kir) current, which is involved in the vasodilation of middle cerebral arteries (MCA) in rat brain, have been described during brain ischemiaireperfusion (I/R). The authors investigate the effects of I/R on Kir current recorded in isolated myocytes from MCA of control rats and from contralateral and ipsilateral MCA of ischemic rats by the whole-cell patch-clamp technique, and the relationship between its alteration and The severity of brain injury. The vascular smooth muscle cells exhibited similar morphologic features in all conditions, and the Kir was present in the three groups of myocytes, exhibiting a characteristic inward rectification and a normal external potassium dependence. The Kir density was significantly reduced in cell of MCA ipsilateral to occlusion with a maximum at −135 mV, whereas there was no difference between control and contralateral cells. This alteration in Kir density in occluded MCA was significantly correlated with severity of brain injury and brain edema. These results suggest that the alteration of Kir density in MCA myocytes after I/R and the consecutive impaired dilation of MCA may contribute to aggravation of the brain injury.