Protection against aspirin-induced human gastric mucosal injury by bosentan, a new endothelin-1 receptor antagonist.

BACKGROUND: Gastric ulceration induced by aspirin and by non-steroidal anti-inflammatory drugs (NSAIDs) is a major clinical problem. The mechanism of injury is unclear. There is evidence that NSAID-induced injury may cause endothelin activation. Endothelin-induced vasoconstriction has been shown to be capable of causing gastric ulceration. AIM: To investigate whether acute gastroduodenal injury induced in humans by aspirin can be prevented by the endothelin-1 antagonist, bosentan. METHODS: Eighteen healthy volunteers each received 5 x 900 mg aspirin every 12 h on three separate occasions (with either placebo, bosentan 700 mg or misoprostol 400 mg). Treatment order was randomized by Latin square design. Subjects were endoscoped and erosions counted before and 90 min after the first and last dose of aspirin. Plasma concentrations of bosentan were measured up to 5 h post-dose. RESULTS: There was a significant reduction in the mean number of erosions in the aspirin plus bosentan and aspirin plus misoprostol groups after the first dose of aspirin, compared with controls (aspirin plus placebo) (P<0.05). This was not sustained after the fifth dose of aspirin in the aspirin plus placebo and aspirin plus bosentan groups, but was still present in the aspirin plus misoprostol group. The mean plasma concentration of bosentan measured 3.5 h post-dose fell from 4510 (95% CI: 2791-6230) ng/mL after the 1st dose to 2508 (95% CI: 1733-3283) ng/mL after the 5th dose (P = 0.02). CONCLUSION: Endothelin receptor antagonism by bosentan can protect the gastric mucosa against aspirin damage. After five doses, bosentan levels fell, possibly because of enzyme induction, and protection was no longer evident. Further investigation is needed to assess whether higher doses would be effective.

Haemodynamics, cardiac conduction and pharmacokinetics of mibefradil (Ro 40-5967), a novel calcium antagonist.

OBJECTIVES: Mibefradil (Ro40-5967) is a chemically novel non-dihydropyridine calcium antagonist. In this phase II study we compared its acute and chronic effects on blood pressure, heart rate and atrioventricular conduction (electrocardiographic PQ interval) with those of verapamil and diltiazem. PATIENTS AND METHODS: After a 4-week placebo run-in, 18 patients with mild to moderate essential hypertension were given single doses of mibefradil (150 mg), slow-release (SR) verapamil (240 mg), diltiazem (240 mg) and placebo at weekly intervals; pharmacokinetics and the effects on blood pressure, heart rate and PQ interval were studied on four 10-h study days. Seventeen of the same patients subsequently underwent 4 weeks of treatment with either mibefradil (100 mg daily; n = 10) or verapamil SR (240 mg daily; n = 7), and on the last day, they attended a further 10-h study day. Two studies were conducted: an acute, single-dose, double-blind, randomly allocated, placebo-controlled, crossover study and a chronic, open-label, randomly allocated, parallel-group study. RESULTS: Mibefradil was well tolerated. In the acute study, the antihypertensive effect (difference from placebo) of mibefradil 150 mg was of slower onset than that of verapamil or diltiazem, but comparable blood pressure reductions had been achieved by 6 h. The mean +/- SD maximal PQ prolongation (difference from placebo) was 15.6 +/- 16.1 ms, compared with 44.0 +/- 22.6 ms for verapamil and 56.0 +/- 48.9 ms for diltiazem (P<0.05 mibefradil versus verapamil; P<0.01 mibefradil versus diltiazem). In the chronic study there were no significant differences during steady-state conditions between mibefradil at 100 mg and verapamil SR at 240 mg in their effects on blood pressure, PQ and heart rate. The mean +/- SD elimination half-life (t1/2) of mibefradil under steady-state conditions was 26.8 +/- 5.5 h (versus an apparent t1/2 of 16.9 +/- 11.1 h for verapamil SR, P<0.05). CONCLUSIONS: Mibefradil is a well-tolerated and efficacious antihypertensive agent well suited to single daily dosing because of its intrinsic long plasma half-life. The effects on both blood pressure and PQ interval are of more gradual onset than those of unmodified verapamil and diltiazem after single doses.

Dissociation between reperfusion induced arrhythmias and increases in ventricular alpha 1 receptor density in the anaesthetised rat.

Using anaesthetised rats we have assessed (1) whether the density of alpha 1 adrenergic receptors increases during coronary artery occlusion, (2) whether any change in density can be associated with the onset of reperfusion induced ventricular fibrillation, and (3) whether alpha 1 blockade with prazosin modifies the incidence of reperfusion induced ventricular fibrillation. The incidence of fibrillation upon reperfusion after 3, 5, 10, 20 and 30 min occlusion was 20, 75, 50, 16 and 10% (n = 10-12 in each group) respectively. alpha 1 Receptor density was measured using [3H]-prazosin in non-ischaemic and ischaemic tissue obtained after 0, 5 and 30 min ischaemia. Receptor density was not significantly altered at the time of maximum incidence of reperfusion induced ventricular fibrillation (5 min occlusion) but did significantly increase in both non-ischaemic and ischaemic tissue after 30 min occlusion, when the incidence of fibrillation upon reperfusion was very low (8%). At this time the values were 17.0(SEM 2.3) and 18.4(0.6)fmol.mg-1 protein in non-ischaemic and ischaemic zones as compared to 10.7(0.6) and 12.8(1.0)fmol.mg-1 protein in sham operated control animals (p less than 0.05 in both cases). Prazosin (0.1 or 1.0 mg.kg-1 body wt intravenously, 5 min prior to coronary occlusion) did not alter the incidence of ventricular fibrillation, ventricular tachycardia or total number of premature ventricular complexes upon reperfusion. We conclude that ischaemia induced changes in alpha 1 receptor density do not parallel changes in vulnerability to reperfusion induced arrhythmias.(ABSTRACT TRUNCATED AT 250 WORDS)

Allopurinol and reperfusion-induced arrhythmias: increased protection by simultaneous administration of anti-oxidant enzymes.

We have assessed whether the xanthine oxidase inhibitor, allopurinol, can afford maximal protection against the formation of reperfusion-induced arrhythmias or whether the addition of free radical scavengers and anti-oxidants can increase this protection. Using an anesthetized rat preparation with transient coronary artery occlusion, we have compared the ability of allopurinol pretreatment alone to that of a combination therapy of allopurinol, superoxide dismutase, and catalase to reduce the incidence of reperfusion-induced arrhythmias. While both regimes reduced the incidence of reperfusion-induced ventricular fibrillation (from 87% to 40%, p less than 0.05 by allopurinol alone; and to 13%, p less than 0.01 by combination therapy), and both treatments eliminated mortality, only combination therapy reduced the incidence of reperfusion-induced ventricular tachycardia (from 87% to 40%, p less than 0.05). Furthermore, using an arrhythmia score analysis, combination therapy was shown to offer significantly greater protection than allopurinol alone. This additional protection afforded by combination therapy was also demonstrated by significant decreases in log10 duration of fibrillation and log10 number of premature ventricular complexes compared with allopurinol alone. Both allopurinol and combination therapy also significantly delayed the ischemia-induced increases in ST segment elevation, although there was no difference between the two drug-treated groups. We conclude from these results that allopurinol does not offer maximal protection against reperfusion-induced arrhythmias and that the addition of more general anti-oxidant therapy can increase this protection.

Reperfusion-induced arrhythmias: a study of the role of xanthine oxidase-derived free radicals in the rat heart.

We have assessed whether oxygen-derived free radicals produced by xanthine oxidase may be an important trigger mechanism in the genesis of reperfusion-induced arrhythmias. We have examined (i) the effects of inhibition of xanthine oxidase by both folic acid solution and amflutizole; (ii) the effects of the inhibitor of xanthine dehydrogenase to xanthine oxidase conversion, soybean trypsin inhibitor; (iii) the effects of administration of superoxide dismutase and catalase, both singly and in combination and (iv) in an isolated rat heart preparation we have investigated the ability of free radical scavengers to reduce reperfusion arrhythmias caused by the infusion of xanthine oxidase and hypoxanthine. The prior administration of folic acid solution, amflutizole, superoxide dismutase, catalase, and superoxide dismutase plus catalase all reduced the incidence of reperfusion-induced arrhythmias and resultant mortality, caused by reperfusion after a transient period of coronary artery occlusion in the anaesthetised rat. Prior administration of soybean trypsin inhibitor significantly reduced mortality. In an isolated, perfused rat heart preparation with temporary coronary artery occlusion, addition of xanthine oxidase-hypoxanthine to the perfusion medium increased the incidence of reperfusion arrhythmias and decreased the total duration of sinus rhythm during reperfusion. Further addition of superoxide dismutase or L-methionine increased significantly the total duration of sinus rhythm. These results suggest that in the rat heart xanthine oxidase may be involved in the genesis of reperfusion-induced arrhythmias.

Ischemia- and reperfusion-induced arrhythmias: beneficial actions of nifedipine.

The effects of nifedipine against ischemia- and reperfusion-induced arrhythmias were investigated using anesthetized rats with transient coronary artery occlusion. Nifedipine (5 micrograms/kg i.v.) administered 10 min prior to occlusion significantly decreased the incidence of arrhythmias occurring during 20-min coronary occlusion. The incidence and duration of reperfusion-induced ventricular fibrillation and subsequent mortality following 5-min coronary occlusion were also significantly reduced by this intervention. However, administration of nifedipine 1 min prior to reperfusion afforded no protection against reperfusion arrhythmias. To investigate whether nifedipine possesses a true antiarrhythmic action or merely extends the ischemic duration prior to reperfusion resulting in maximal rhythm disturbances, reperfusion was initiated after 3, 5, 7, 10, 20, and 30 min of ischemia. Nifedipine reduced the incidence of reperfusion-induced ventricular fibrillation after all ischemic intervals, with no change in the time of peak vulnerability to reperfusion arrhythmias. Measurements of coronary flow with 153Gadolinium microspheres indicated that flow within ischemic tissue relative to that in normal tissue was significantly increased by nifedipine. Thus, administration of nifedipine prior to occlusion affords a protective effect against ischemia- and reperfusion-induced arrhythmias, and this action is not due to extension of the ischemic duration prior to reperfusion resulting in maximal rhythm disturbances.

Creatine phosphate and protection against reperfusion-induced arrhythmias in the rat heart.

An isolated perfused working rat heart preparation was used to assess the effect of including creatine phosphate (10 mmol/l) in the perfusion fluid of hearts subjected to aerobic perfusion (20 min), regional ischaemia (15 min) and reperfusion (2 min). Creatine phosphate had no detectable effect upon pre-ischaemic, ischaemic or post-ischaemic contractile function, it also had no statistically significant effect upon myocardial tissue ATP content. However, creatine phosphate was found to afford striking protection against reperfusion-induced arrhythmias. The incidence of ventricular fibrillation was reduced from over 80% (13/16) in the control group to 10% in the creatine phosphate-treated group (P less than 0.001). Possible mechanisms underlying the anti-arrhythmic effects of creatine phosphate were investigated using isolated rat papillary muscles superfused with or without added creatine phosphate (10 mmol/l). During aerobic superfusion at 37 degrees C creatine phosphate did not cause any statistically significant changes in contractile (developed tension) or electrophysiological (dV/dtmax and action potential duration) indices. Creatine phosphate did however influence the extent to which hypoxia (10 min) and reoxygenation (10 min) altered tension and electrophysiological characteristics. It accelerated the hypoxia-induced decline in developed tension and also the reoxygenation-induced recovery of developed tension. Relatively small changes in dV/dtmax and action potential duration were observed during hypoxia and these rapidly normalized during reoxygenation. In general creatine phosphate acted to exacerbate any changes during hypoxia and accelerate the recovery during reoxygenation. While some of the electrophysiological changes observed would indicate an anti-arrhythmic effect, they were relatively small and perhaps insufficient to explain fully the potent anti-arrhythmic properties of creatine phosphate.

Calcium antagonists and myocardial protection: a comparative study of the functional, metabolic and electrical consequences of verapamil and nifedipine as additives to the St. Thomas' cardioplegic solution.

Using an isolated rat heart preparation as a model of cardiopulmonary bypass and ischemic arrest, a comparative study has been undertaken in order to characterize the functional, metabolic and electrophysiological consequences resulting from the addition of dl-verapamil or nifedipine to the St. Thomas' Hospital cardioplegic solution. Hearts (n = 6 in each group) were subjected to cardioplegic infusion with the St. Thomas' solution with or without added verapamil (1.1 micromoles/liter) or nifedipine (0.075 micromoles/liter). After 35 minutes of normothermic (37 degrees C) ischemic arrest, reperfusion was initiated and functional recovery was measured and expressed as a percent of its pre-ischemic control value. Inclusion of nifedipine in the cardioplegic solution improved the post-ischemic recovery of cardiac output from its control value of 59.8 +/- 3.0% to 80.0 +/- 2.5%. The temporal characteristics for the post-ischemic recovery of electrical activity and contractile performance were uncomplicated and similar to control hearts. Inclusion of verapamil also improved the protective properties of the St. Thomas' solution with cardiac output recovering to 76.8% +/- 2.8%. However, in contrast to the control and nifedipine groups, the profile for functional recovery was complex. After an early initial recovery, pressure development declined for 0.5 to 6.0 minutes. This occurred despite the recovery of electrical activity. Hearts then exhibited a second phase of recovery where pressure development returned to normal and this was sustained for the duration of the experiment. Analysis of electrocardiographic characteristics revealed a significant prolongation of the P-P and P-Q interval during the first 10 minutes of reperfusion in the verapamil group.(ABSTRACT TRUNCATED AT 250 WORDS)

Reperfusion-induced ventricular fibrillation. Modification by pharmacological agents.

We have assessed the ability of several of the main groups of antiarrhythmic agents to modify the incidence of reperfusion-induced ventricular fibrillation in the isolated working rat heart preparation with transient coronary artery occlusion. Hearts were perfused with Krebs-Henseleit medium containing 5 microM epinephrine to provide some level of exogenous catecholamine support. Compounds selected were: the fast sodium channel inhibitors lignocaine (1 and 10 microM) and prenylamine (4 microM) (the latter also possessing slow calcium channel antagonistic actions); the beta-adrenergic blocking agents oxprenolol (1.2 microM), timolol (0.13 microM), metoprolol (1.0 microM), and acebutolol (5.6 microM); and the slow calcium channel antagonist nifedipine (0.05 and 0.5 microM). After 15 min of coronary artery occlusion, over 90% of control hearts fibrillated 30-60 sec after the onset of reperfusion. Drugs reduced this to the following: prenylamine, 0% (p less than 0.001); 1 microM lignocaine, 83%; 10 microM lignocaine, 33% (p less than 0.01); oxprenolol, 92% (NS); timolol, 92% (NS); metoprolol, 42% (p less than 0.01); acebutolol, 67% (p less than 0.05); 0.05 microM nifedipine, 83% (NS); and 0.5 microM nifedipine, 67% (NS). Thus, inhibition of the fast inward sodium channel with agents such as prenylamine and lignocaine, (when begun before coronary-artery occlusion) offers maximal protection against reperfusion-induced ventricular fibrillation, while beta-blockade with timolol and oxprenolol and slow calcium channel inhibition with nifedipine do not offer any significant protection. The beta-blocking agents metoprolol and acebutolol produce a partial reduction that may be due to a membrane-stabilizing action, rather than to beta-blockade.

Temporal and spatial characteristics of evolving cell injury during regional myocardial ischemia in the dog: the "border zone" controversy.

An open chest dog heart with multiple coronary ligations was used to define the temporal and spatial characteristics of injury evolving during regional ischemia. With the use of a multiple (40 sample) biopsy device, adjacent transmural biopsy specimens were obtained from the transition zone between normal and ischemic tissue after 5, 30, 45, 60 and 120 minutes of ischemia. The first 1.8 mm of epicardial tissue was taken for the analysis of flow and metabolites. The results confirmed the existence of a sharp interface of flow and metabolism in the epicardial lateral plane at the boundary of the ischemic zone. There was no significant zone of intermediate injury (flow and metabolism being depressed uniformly throughout the ischemic area). Comparison of the distribution of flow determined by radiolabeled gadolinium-153 at onset of ischemia with that indicated by radiolabeled tin-113 microspheres given at the end of various periods of ischemia revealed no change in the position or steepness of the flow interface at any time during the first 2 hours of ischemia. This observation, together with the absence of any major redistribution or enhancement of residual flow to the ischemic zone, indicated that there was little or no significant collateralization between 5 and 120 minutes. Analysis of the adenosine triphosphate (ATP) content revealed a rapid depletion during the first 5 minutes of ischemia; the content then remained essentially unchanged until 30 minutes, after which time a second phase of accelerated ATP depletion was observed until 45 minutes. ATP content then remained relatively constant up to 2 hours.

Metabolic and flow correlates of myocardial ischaemia.

Seven hundred and twenty three biopsies were obtained from 20 dogs after coronary artery ligation for 5, 30, 45, 60 or 120 min (n = 4 dogs for each group). Paired values for blood flow (radioactive microspheres) and tissue ATP content were obtained for each biopsy and related to the duration of ischaemia. Three states of ischaemic injury could be recognised. In the first, designated as "tolerable" ischaemia, coronary flow was reduced by up to 50%. In this flow band, ATP depletion was relatively small and time-independent. If flow was reduced by 60 to 80%, a state of "critical" ischaemia was identified where ATP depletion was both flow- and time-dependent and, in this relatively narrow range, small changes in flow or duration could result in major changes in ATP depletion. With severe flow reductions of greater than 80%, designated as "lethal" ischaemia, a complex pattern emerged such that with up to 30 min of ischaemia, ATP fell progressively with increasing time and flow deprivation. Between 30 and 45 min ATP depletion accelerated and beyond 45 min the time-dependency disappeared with tissue ATP content remaining relatively constant at a severely depressed level for several hours. All of these results are discussed in the light of earlier proposals (disputed) that tissue injury as expressed by ATP depletion can be predicted by the product of ischaemic duration and flow deprivation.

Characterization of the lateral interface between normal and ischemic tissue in the canine heart during evolving myocardial infarction.

A new nonrotating multiple biopsy device has been developed to allow the rapid, simultaneous and contiguous sampling of cardiac muscle in the large mammalian heart. Each cutter obtains 40 adjacent transmural left ventricular biopsy samples, each of 4 mm section. The epicardial 1.8 mm of each biopsy section was analyzed for flow, adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, creatine phosphate and lactate. Use of this procedure in the dog heart 30 minutes after coronary arterial ligation permitted characterization of the nature of flow and metabolic gradients as the sampling site moved from the core of an areas of regional ischemia to the surrounding normal tissue. These studies of metabolic and flow geometry in the lateral plane indicate the existence of a sharp interface of flow and metabolism between normal and ischemic tissue. The absence of intermediate levels of flow and metabolism indicate that, in the lateral plane at least, a quantitatively significant and spatially identifiable "border zone" region does not exist. However, these findings, do not preclude the existence of such a zone of jeopardized tissue in the transmural plane or the occurrence of a temporal border zone to which interfaces of flow and metabolism may migrate with time.