Effects of iloprost, a stable prostacyclin analog, on exercise capacity and platelet aggregation in stable angina pectoris

Functional and structural adaptations of the coronary macro- and micro-vasculature to regular aerobic exercise by activation of physiological, cellular and molecular mechanisms: Esc Working Group on Coronary Pathophysiology & Microcirculation Position Paper

Regular aerobic exercise (RAEX) elicits several positive adaptations in all organs and tissues of the body, culminating in improved health and well-being. Indeed, in over half a century, many studies have shown the benefit of RAEX on cardiovascular outcome in terms of morbidity and mortality. RAEX elicits a wide range of functional and structural adaptations in the heart and its coronary circulation, all of which are to maintain optimal myocardial oxygen and nutritional supply during increased demand. Although there is no evidence suggesting that oxidative metabolism is limited by coronary blood flow (CBF) rate in the normal heart even during maximal exercise, increased CBF and capillary exchange capacities have been reported. Adaptations of coronary macro- and microvessels include outward remodeling of epicardial coronary arteries, increased coronary arteriolar size and density, and increased capillary surface area. In addition, there are adjustments in the neural and endothelial regulation of coronary macrovascular tone. Similarly, there are several adaptations at the level of microcirculation, including enhanced smooth muscle dependent pressure-induced myogenic constriction and upregulated endothelium-dependent flow-/shear-stress-induced dilation, increasing the range of diameter change. Alterations in the signaling interaction between coronary vessels and cardiac metabolism have also been described. At the molecular and cellular level, ion channels are key players in the local coronary vascular adaptations to RAEX, with enhanced activation of influx of Ca2+ contributing to the increased myogenic tone (via voltage gated Ca2+ channels) as well as the enhanced endothelium-dependent dilation (via TRPV4 channels). Finally, RAEX elicits a number of beneficial effects on several hemorheological variables that may further improve CBF and myocardial oxygen delivery and nutrient exchange in the microcirculation by stabilizing and extending the range and further optimizing the regulation of myocardial blood flow during exercise. These adaptations also act to prevent and/or delay the development of coronary and cardiac diseases.

Effects of chronic nitric oxide synthase inhibition on V'O2max and exercise capacity in mice

Acute inhibition of NOS by L-NAME (N^ω-nitro-L-arginine methyl ester) is known to decrease maximal oxygen consumption (V'O_2max) and impair maximal exercise capacity, whereas the effects of chronic L-NAME treatment on V'O_2max and exercise performance have not been studied so far. In this study, we analysed the effect of L-NAME treatment, (LN2 and LN12, respectively) on V'O_2max and exercise capacity (in maximal incremental running and prolonged sub-maximal incremental running tests), systemic NO bioavailability (plasma nitrite (NO₂^-) and nitrate (NO₃^-)) and prostacyclin (PGI₂) production in C57BL6/J mice. Mice treated with L-NAME for 2 weeks (LN2) displayed higher V'O_2max and better running capacity than age-matched control mice. In LN2 mice, NO bioavailability was preserved, as evidenced by maintained NO₂^- plasma concentration. PGI₂ production was activated (increased 6-keto-PGF_1α plasma concentration) and the number of circulating erythrocytes (RBC) and haemoglobin concentration were increased. In mice treated with L-NAME for 12 weeks (LN12), NO bioavailability was decreased (lower NO₂^- plasma concentration), and 6-keto-PGF_1α plasma concentration and RBC number were not elevated compared to age-matched control mice. However, LN12 mice still performed better during the maximal incremental running test despite having lower V'O_2max. Interestingly, the LN12 mice showed poorer running capacity during the prolonged sub-maximal incremental running test. To conclude, short-term (2 weeks) but not long-term (12 weeks) treatment with L-NAME activated robust compensatory mechanisms involving preservation of NO2- plasma concentration, overproduction of PGI₂ and increased number of RBCs, which might explain the fully preserved exercise capacity despite the inhibition of NOS.

Effects of 1-Methylnicotinamide (MNA) on Exercise Capacity and Endothelial Response in Diabetic Mice

1-Methylnicotinamide (MNA), which was initially considered to be a biologically inactive endogenous metabolite of nicotinamide, has emerged as an anti-thrombotic and anti-inflammatory agent with the capacity to release prostacyclin (PGI2). In the present study, we characterized the effects of MNA on exercise capacity and the endothelial response to exercise in diabetic mice. Eight-week-old db/db mice were untreated or treated with MNA for 4 weeks (100 mg·kg-1), and their exercise capacity as well as NO- and PGI2-dependent response to endurance running were subsequently assessed. MNA treatment of db/db mice resulted in four-fold and three-fold elevation of urine concentrations of MNA and its metabolites (Met-2PY + Met-4PY), respectively (P<0.01), but did not affect HbA1c concentration, fasting glucose concentration or lipid profile. However, insulin sensitivity was improved (P<0.01). In MNA-treated db/db mice, the time to fatigue for endurance exercise was significantly prolonged (P<0.05). Post-exercise Δ6-keto-PGF1α (difference between mean concentration in the sedentary and exercised groups) tended to increase, and post-exercise leukocytosis was substantially reduced in MNA-treated animals. In turn, the post-exercise fall in plasma concentration of nitrate was not affected by MNA. In conclusion, we demonstrated for the first time that MNA improves endurance exercise capacity in mice with diabetes, and may also decrease the cardiovascular risk of exercise.

Coronary and muscle blood flow during physical exercise in humans; heterogenic alliance

In this review, we present the relation between power generation capabilities and pulmonary oxygen uptake during incremental cycling exercise in humans and the effect of exercise intensity on the oxygen cost of work. We also discuss the importance of oxygen delivery to the working muscles as a factor determining maximal oxygen uptake in humans. Subsequently, we outline the importance of coronary blood flow, myocardial oxygen uptake and myocardial metabolic stability for exercise tolerance. Finally, we describe mechanisms of endothelium-dependent regulation of coronary and skeletal muscle blood flow, dysregulation of which may impair exercise capacity and increase the cardiovascular risk of exercise.

Prediction of long-term ischemic events by noninvasively assessed coronary flow reserve

BACKGROUND

Coronary flow reserve (CFR) by adenosine echocardiography in left anterior descending (LAD) or posterior descending coronary arteries may predict clinical outcome.

METHODS

We used models accounting (Cox's model) or not (logistic regression and neural network) for time to event and either considered (forced models) or not (stepwise logistic regression and neural network models) all among 21 covariates to predict 1-year composite events after LAD CFR.

RESULTS

There were 553 consecutive patients with coronary artery disease (CAD): 89 patients had also posterior descending CFR. During 1-year follow-up 328 patients were event-free, 35 had composite ischemic events and 190 underwent short-term revascularization. LAD and posterior descending CFR (respectively, 1.53 ± 0.83, N = 225 and 1.84 ± 0.80, N = 42) were significantly (P < 0.0001) lower in patients with events (or with revascularization following CFR measurement) than in those without (respectively, 3.13 ± 0.84, N = 328, and 2.53 ± 0.72, N = 47). Using LAD CFR as a continuous covariate, by both forced Cox's and logistic regression, coefficients (t values, respectively, -14.11 and -10.19) were significant (both P < 0.00001) to predict outcome. Global predictive accuracies by neural network, adopting a receiver operating characteristic areas under the curve (ROC) assessment, were excellent (>0.91) and the role of LAD CFR among predictors was overwhelming. Other indices of myocardial ischemia and the presence of coronary stenoses or previous infarction did not modify the multivariable predictive role of LAD CFR. When patients with revascularization were discounted, the LAD CFR predictive role was the same.

CONCLUSIONS

Thus, adenosine echocardiography-based LAD CFR predicts 1-year composite ischemic events in patients with CAD, independent of the multivariable model adopted. Posterior descending CFR also has a role.

Selection of optimal dose of beta-blocker treatment in myocardial infarction patients based on changes in synchronization between 0.1 Hz oscillations in heart rate and peripheral microcirculation

BACKGROUND

Selection of the optimal dose of beta-blocker treatment in myocardial infarction (MI) patients is problematic because of a lack of well-established guidelines.

METHODS

We evaluated changes in synchronization between 0.1 Hz oscillations in heart rate (HR) and plethysmographic peripheral microcirculation in response to a tilt-table test and to 3-month treatment with the highest tolerated beta-blocker (metoprolol) dose in 43 patients aged between 41 and 77 years with acute MI 6 months prior to the start of the study. Before the study the patients were treated with small doses of beta-blocker. Phase differences between HR and peripheral microcirculation oscillations were used to measure the degree of synchronization (S), and relative change in S from horizontal position was used to characterize the response to vertical tilt.

RESULTS

Two groups of MI patients matched for clinical characteristics were identified on the basis of the results. The first group was composed of patients with decreased S as a response to vertical tilt at the beginning of the study. The patients with increased S during vertical tilt before treatment with the highest tolerated beta-blocker dose were attributed to the second group. The response to vertical tilt in the first group of patients was postulated to indicate the need to increase beta-blocker dose, and in turn, the response in the second group to indicate an already adequate beta-blocker dose.

CONCLUSION

Assessment of synchronization of 0.1  Hz HR and peripheral microcirculation oscillations as a response to a tilt test can possibly be used as a guideline for selecting beta-blocker dose in post-MI patients.

Lack of association of A-6G polymorphism of AGT gene with essential hypertension in the Chinese population

BACKGROUND

The angiotensinogen (AGT) A-6G gene polymorphism has been indicated to be related to the susceptibility of essential hypertension. However, the results are still unclear.

OBJECTIVE AND METHODS

To survey the relationship between AGT A-6G gene polymorphism and essential hypertension, 18 separate studies with 9306 patients were analyzed through meta-analysis. The random-effect model was used to calculate the pooled odds ratio (OR) and its corresponding 95% confidence interval (CI).

RESULTS

In this AGT A-6G gene polymorphism and essential hypertension meta-analysis of the Chinese population, the distribution of the G-allele frequency was 0.23 for the essential hypertension group and 0.21 for the control group. The association between the AGT A-6G gene polymorphism and essential hypertension in the entire sample population was not significant. The pooled OR for the frequency of the G allele was 1.10 (95% CI 0.96 to 1.27, Pheterogeneity < 0.00001, P = 0.17). In the stratified analysis by ethnicity, a significant association in Li and Mongolian ethnicities (P ≤ 0.05) was achieved. However, no significant association was found in other ethnicities such as Han, Tibetan, Kazakh, Bai and Yi (P > 0.05).

CONCLUSIONS

The current meta-analysis suggested that AGT A-6G gene polymorphism might not be related to the increased risk of essential hypertension in the entire Chinese population. However, the G-allele of AGT A-6G might predispose to essential hypertension in the Li and Mongolian ethnicities.

Protective mechanism of nicorandil on rat myocardial ischemia-reperfusion

OBJECTIVES

To study the protective mechanism of nicorandil on myocardial ischemia-reperfusion injury.

METHODS

Fifty rats were randomly divided into five groups, four of which were operated on to produce myocardial ischemia-reperfusion. Nicorandil (5 mg/kg) was administrated by intravenous injection to three of the groups. The myocardial ultrastructure was observed by electron microscope. The expression levels of the antiapoptotic protein Bcl-2 and the pro-apoptotic protein Bax were detected by immunohistochemical staining with rhodamine 123. The mitochondrial membrane potential was detected by spectrophotometry.

RESULTS

The activity of lactate dehydrogenase (LDH) and malondialdehyde (MDA) content was decreased and the activity of superoxide dismutase (SOD) was increased in the three nicorandil groups, compared with those in the group without nicorandil (P < 0.01, P < 0.05). The positive staining level of the expressed Bcl-2 was increased and the expressed Bax was decreased (P < 0.01) in the three nicorandil groups, compared with those in the group without nicorandil. The mitochondrial inner membrane potential was increased in the three nicorandil groups compared with that in the group without nicorandil (P < 0.05).

CONCLUSION

A suitable level of nicorandil has a protective effect on rats' myocardial ischemia-reperfusion injury, and is mainly based on the opening of the mitochondrial KATP channel and the lowing of Ca overload.

The level of serum bilirubin associated with coronary lesion types in patients with coronary artery disease

BACKGROUND

Serum bilirubin has been proven to be associated with coronary artery disease (CAD). However, how serum bilirubin is related to the complexity of coronary artery lesions is still unknown.

METHODS AND RESULTS

One thousand two hundred and sixty patients (men 775, 61.5%, mean age, 59.3  ±  8.2 years) diagnosed with unstable angina were enrolled in the study. Patients were categorized into three major groups and group III was further divided into four subgroups according to the guidelines of AHA/ACC 1993 described in the Methods section. The total serum bilirubin levels showed significant differences among the three major groups (group I vs. group II, 14.8 ± 5.8 vs. 13.7 ± 4.7 μmol/l, P=0.017; group I vs. group III, 14.8 ± 5.8 vs. 12.6 ±  4.4 μmol/l, P<0.001; group II vs. group III, 13.7 ± 4.7 vs. 12.6 ± 4.4 μmol/l, P=0.009). The difference was further seen among the subgroups. Logistic regression analysis demonstrated that age, male sex, histories of hypertension and diabetes, and total serum bilirubin were independent risk factors for CAD. However, in the subgroups, only age, male sex, history of hypertension and total serum bilirubin were associated with CAD. Total serum bilirubin showed the strongest relationship (odds ratio=0.95, 95% confidence interval 0.91-0.98, P=0.001).

CONCLUSION

Total serum bilirubin level is an independent risk factor for CAD. It has a strong relationship with coronary artery lesion types.

A large left ventricular pseudoaneurysm evaluated with multimodality cardiac imaging

Rarely, the rupture of the free wall of the left ventricle is contained by an adherent pericardium, creating a pseudoaneurysm. This clinical finding calls for emergency surgery. However, true aneurysms, if no ruptures are detectable and myocardium wall integrity is confirmed, can often be managed medically. Therefore, the accurate diagnosis of these conditions is clinically important. In this report, we present a case of large left ventricular pseudoaneurysm evaluated with multimodality cardiac imaging.

Relationship of fragmented QRS complexes with inadequate coronary collaterals in patients with chronic total occlusion

BACKGROUND

Fragmented QRS (fQRS) complexes are defined as various RSR' patterns (≥1 R' or notching of S wave or R wave) in two contiguous leads corresponding to a major coronary artery territory. In previous studies, fQRS has been associated with increased morbidity and mortality, sudden cardiac death and recurrent cardiovascular events (CVEs). The causative relationship between fQRS and cardiac fibrosis has been shown in prior studies. The association between inadequate (poor) coronary collaterals and presence of fQRS has not comprehensively been studied in patients with chronic total occlusion (CTO) until now. We tested the hypothesis that the presence of fQRS is associated with inadequate coronary collateral growth.

METHODS

This study had a cross-sectional observational design. The study population consisted of patients who underwent coronary angiography with the suspicion of coronary artery disease at our institution in an outpatient manner. Patients who had CTO in at least one major epicardial coronary artery were included. Coronary angiograms of 148 eligible patients from our database were analyzed again. Ninety-three patients had good and 55 had poor collateral development according to the Cohen-Rentrop method.

RESULTS

Patients with poor collateral development had higher plasma glucose (130 ± 54 vs. 116 ± 33 mg/dl, P = 0.047) and an older age (65 ± 10 vs. 61 ± 10  years, P = 0.042) in comparison to patients with good collateral growth. The presence and number of fQRS were higher in the poor collateral group than the good collateral group (64 vs. 32%, P < 0.001 and 2.3 ± 2.4 vs. 1.2 ± 2.0, P = 0.002, respectively). Left ventricular ejection fraction was significantly lower in the poor collateral group than the good collateral group (45 ± 11 vs. 51 ± 13, P = 0.014). There was a significant correlation between number of fQRSs and the echocardiographic wall-motion abnormality score (r = 0.662, P < 0.001). In multivariate analysis, only the presence of fQRS was independently related to poor collateral development (odds ratio, 3.559; 95% confidence interval, 1.708-7.415, P = 0.001).

CONCLUSION

We found that fQRS was independently related to inadequate coronary collaterals in patients with CTO. fQRS, which may be derived from the effects of myocardial ischemia or scar on myocardial electricity at the cellular level, can represent inadequate coronary collateral development in patients with CTO.

Endurance training increases exercise-induced prostacyclin release in young, healthy men--relationship with VO2max

In the present study, we evaluated the effect of 5 weeks of moderate-intensity endurance training on the basal and exercise-induced systemic release of prostacyclin (PGI(2)), as assessed by plasma 6-keto-PGF(1 alpha) concentration. Twelve physically active young men with the following characteristics participated in this study (the mean +/- SD): age, 22.7 +/- 2.0 years; body mass, 76.8 +/- 8.9 kg; BMI, 23.48 +/- 2.17 kg x m(-2); and maximal oxygen uptake (VO(2 max)), 46.1 +/- 4.0 ml x kg(-1) x min(-1). Plasma 6-keto-PGF(1 alpha) concentrations were measured in venous blood samples taken prior to the exercise and at exhaustion (at VO(2 max)) before and after completing the training protocol. On average, the training resulted in a significant increase in VO(2 max) (p = 0.03), power output at VO(2 max) (p = 0.001) and a significant increase (p = 0.05) in the net-exercise-induced increase in plasma 6-keto-PGF(1 alpha) concentration (Delta 6-keto-PGF(1 alpha) i.e., the difference between the end-exercise and pre-exercise 6-keto-PGF(1 alpha) concentrations). No effect of training on the basal PGI(2) concentration was found. Interestingly, within the study sample (n = 12), two subgroups could be defined with a differential pattern of response with respect to Delta 6-keto-PGF(1 alpha) concentrations. In one subgroup (n = 7), a significant increase in Delta 6-keto-PGF(1 alpha) concentration after training was found (p < 0.02) (responders). This enhancement in the exercise-induced PGI(2) release was accompanied by a significant (p < 0.05) increase in VO(2 max) after training. In contrast, in another subgroup (n = 5), there was no observed effect of training on the Delta 6-keto-PGF(1 alpha) concentration and the VO(2 max) after training (non-responders). In both of these subgroups, training did not influence the basal PGI(2) concentration. In conclusion, the endurance training resulted in the adaptive augmentation of the systemic release of PGI(2) in response to exercise, which plays a role in the training-induced increase in VO(2 max) in young, healthy men. The impairment of the training-induced augmentation of PGI(2) release in response to exercise demonstrated in the non-responders subgroup may predispose them to increased cardiovascular risk during vigorous exercise.

Pulmonary Arterial Hypertension

The treatment of pediatric pulmonary arterial hypertension (PAH) is challenging due to the serious nature of the disease, its rapid progression, and the limited treatment options available. While oral calcium channel antagonists and continuous intravenous epoprostenol have been used successfully for over a decade, novel treatment options - including prostacyclin analogs, endothelin receptor antagonists, and phosphodiesterase-5 inhibitors - may change the course of this disease for many children in the future.Prostacyclin analogs offer the benefit over continuous intravenous epoprostenol of an alternative delivery system. However, the efficacy of these medications compared with intravenous epoprostenol and the risk/benefits of each analog need to be weighed in future trials, which need to include larger numbers of pediatric patients to optimize therapy and outcome for individual children with PAH.For patients who do not have an acute response to vasodilator testing or have failed treatment with oral calcium channel antagonists, endothelin receptor antagonists may offer a viable treatment option. Furthermore, in the future, the addition of endothelin receptor antagonists to long-term therapy with calcium channel antagonists or to epoprostenol or a prostacyclin analog may increase the overall efficacy of treatment of PAH. Large multi-institutional randomized trials to determine whether sildenafil is effective and safe for the long-term treatment of PAH in children are in progress.A comprehensive review of these newer agents with an emphasis on the pathobiology/pathophysiology of PAH provides insight into the future management of pediatric PAH patients.

Pulmonary arterial hypertension in children

Pulmonary arterial hypertension is a serious progressive condition with a poor prognosis if not identified and treated early. Because the symptoms are nonspecific and the physical findings can be subtle, the disease is often diagnosed in its later stages. Remarkable progress has been made in the field of pulmonary arterial hypertension over the past several decades. The pathology is now better defined, and significant advances have occurred in understanding the pathobiologic mechanisms. Risk factors have been identified, and the genetics have been characterized. Advances in technology allow earlier diagnosis as well as better assessment of disease severity. Therapeutic modalities such as new drugs, e.g., epoprostenol, treprostinil, and bosentan, and surgical/interventional options, e.g., transplantation and atrial septostomy, which were unavailable several decades ago, have had a significant impact on prognosis and outcome. Thus, despite our inability to cure pulmonary arterial hypertension, advances in medical treatments over the past two decades have resulted in significant improvement in outcomes for children with various forms of pulmonary arterial hypertension. This report is a review the current state of the art for pulmonary arterial hypertension in 2004, with an emphasis on childhood pulmonary arterial hypertension and specific recommendations for current practice and future directions.

Novel therapeutics for the treatment of paediatric pulmonary arterial hypertension

The treatment of paediatric pulmonary arterial hypertension is challenging due to the serious nature of the disease, its rapid progression and the limited treatment options available. However, recent advances in the treatment of pulmonary arterial hypertension may offer significant improvements for patients suffering from this condition. Novel treatment options include prostacyclin analogues and endothelin receptor antagonists. A comprehensive review of the newer agents, with an emphasis on the pathobiology/pathophysiology of pulmonary arterial hypertension provides insight into future management of paediatric pulmonary arterial hypertension.

Treatment of pulmonary hypertension with the continuous infusion of a prostacyclin analogue, iloprost

OBJECTIVE

To compare prostacyclin with an analogue, iloprost, in treatment of severe pulmonary hypertension.

PATIENTS

Eight patients with severe pulmonary hypertension: primary in five, thromboembolic pulmonary hypertension in three.

METHODS

All patients underwent right heart catheterisation. Mean (SEM) right atrial pressure was 9.9 (2.2) mm Hg, mean pulmonary artery pressure 67.4 (3.0) mm Hg, cardiac index 1.75 (0.13) l/min/m2 and mixed venous oxygen saturation 59.1(3.1)%. Continuous intravenous epoprostenol (prostacyclin, PGI2) or iloprost was given for phase I (three to six weeks); the patients were then crossed over to receive the alternate drug in an equivalent phase II.

MAIN OUTCOME MEASURES

Exercise tolerance was measured at baseline and at the end of phase I and II with a 12 minute walk; distance covered, rest period, percentage drop in arterial oxygen saturation (delta Sao2%) and percentage rise in heart rate (delta HR%).

RESULTS

Walking distance covered rose from (mean (SEM)) 407.5 (73) to 591 (46) m with PGI2 (p = 0.004) and to 602.5 (60) m while on iloprost (p = 0.008). Rest period decreased from 192 (73) seconds at baseline to 16 (16) seconds with PGI2 (p = 0.01) and to 58 (34) seconds with iloprost (p = 0.008). Delta HR% was 37.5(6)% at baseline, 35(3)% on PGI2, and 24(6)% on iloprost (p = 0.04).

CONCLUSIONS

Both intravenous PGI2 and iloprost caused significant improvement in exercise tolerance. Iloprost offers an alternative to PGI2 treatment of severe pulmonary hypertension.

Effects of beraprost sodium, a new prostaglandin I2 analog, on parameters of hemostasis, fibrinolysis, and myocardial ischemia in patients with exertional angina

The purpose of this study was to investigate the effects of beraprost sodium, a stable prostacyclin analog, on the parameters of hemostasis, fibrinolysis, and myocardial ischemia in patients with exertional angina. Thirty-one patients with exertional angina who had significant organic coronary artery stenosis in at least one of the three major coronary arteries were selected. All patients underwent quantitative exercise thallium-201 emission computed tomography before and 1 month after 120 micrograms per day of beraprost sodium administration. Before exercise, blood samples were collected from 8:30 a.m. to 9:30 a.m. after the patients had been lying in bed undisturbed for at least 10 minutes. Plasma platelet factor 4 (PF4), fibrinopeptide A (FPA), tissue plasminogen activator antigen (t-PA), and plasminogen activator inhibitor-1 activity (PAI-1) were measured. There were no significant differences in exercise parameters on both exercise tests. However, both the extent and severity scores of ischemia were significantly aggravated (p < 0.05 for both) during beraprost sodium administration. Plasma FPA levels decreased significantly during beraprost sodium administration (p < 0.01). Likewise, plasma PF4 levels decreased significantly during beraprost sodium administration (p < 0.05). As for plasma t-PA antigen levels, there was no significant difference before versus during beraprost sodium administration. Plasma PAI-1 activity levels decreased significantly during beraprost sodium administration (p < 0.05). The results indicate that beraprost sodium has strong antithrombogenic properties. However, its aggravation of myocardial ischemia may limit clinical usage.

Pharmacokinetics of tissue-type plasminogen activator during acute myocardial infarction in men. Effect of a prostacyclin analogue

BACKGROUND

Coronary reocclusion complicates the thrombolytic therapy of acute myocardial infarction despite the routine use of aspirin. This is consistent with experimental studies demonstrating that multiple agonists, in addition to thromboxane A2, mediate the platelet activation underlying reocclusion. Consequently, a more potent antiplatelet therapy with a broader spectrum of activity than aspirin may be required in this setting. Prostacyclin and its more stable analogue, iloprost, inhibit platelet aggregation to all known agonists and exert an additional effect over aspirin alone. Experiments in animal models have demonstrated, however, that iloprost increases the clearance of tissue-type plasminogen activator (t-PA) and impairs thrombolysis in vivo. This study examines whether a similar interaction occurs in humans.

METHODS AND RESULTS

Twelve patients with acute myocardial infarction received t-PA intravenously, 60 mg in the first hour and a maintenance infusion of 13.3 mg/hr for 3 hours. Patients were assigned in a double-blind fashion to iloprost (2 ng/kg/min) or placebo following the initial 90 minutes of the maintenance infusion of t-PA. Iloprost decreased mean arterial blood pressure (-10 +/- 2.9 mm Hg, p less than 0.05) but did not alter heart rate. Steady-state plasma iloprost concentration was 591 +/- 64 pmol/l. At this concentration, iloprost markedly inhibited platelet aggregation in vitro, particularly in the presence of aspirin. Steady-state clearance of t-PA was unchanged by iloprost (454 +/- 65 versus 443 +/- 136 ml/min in controls, p = NS). Furthermore, neither elimination kinetics nor plasma protein binding of t-PA was altered by iloprost.

CONCLUSIONS

At plasma levels that exert a potent antiplatelet effect, iloprost did not alter the pharmacokinetics of t-PA in men. Prostacyclin analogues may prove useful as an adjunct to plasminogen activators, particularly in patients at high risk for thrombotic reocclusion.

Effects of laser-generated tissue debris on aggregation of human platelets

This study examined the effects of laser-generated tissue debris from thrombus, atheroma, and normal aorta on platelet aggregation. Debris supernatant and suspension from lased thrombus induced dose-related aggregation, maximal at 48 +/- 12% and 65 +/- 2%, respectively. Debris suspension from normal aorta induced maximal aggregation of 35 +/- 12%, but the debris from atheromatous aorta surprisingly had no effect on platelet aggregation. The debris particle count was in the range of 10(10) to 10(12) per liter. Aspirin, 0.2 and 2.0 mmol/L, only weakly inhibited the debris-induced aggregation, and heparin up to 10 U/ml was ineffective. However, iloprost reduced aggregation to 40 +/- 11% of control at 0.3 ng/ml, and totally abolished it at 3 ng/ml. Soluble and particulate laser-generated debris from vascular tissue and thrombus may cause platelet aggregation in vitro. This may have implications for laser coronary angioplasty.

Clinical efficacy of a stable prostacyclin analog, iloprost, in diabetic neuropathy

Iloprost, a stable prostacyclin analog, was evaluated clinically for its ability to ameliorate the symptoms of peripheral neuropathy associated with diabetes. In an open, nonrandomized trial, 13 diabetic patients with neuropathy but without proliferative retinopathy received an intravenous infusion of Iloprost at a dose of 10 micrograms, at a rate of 0.1 micrograms/kg/h, twice daily for two weeks. The administration of Iloprost relieved the majority of such subjective symptoms as pain, numbness or sensation of cold and to a lesser extent, such autonomic symptoms as dizziness. In contrast, there was little evidence of objective improvement, e.g., in motor nerve conduction velocity. Iloprost treatment significantly inhibited the platelet aggregation rate stimulated by collagen in vitro. In the one patient tested, thermography revealed an increase in skin temperature by more than 2 degrees C. Side effects associated with Iloprost included headache (3 patients) or aggravation of pain in the extremities (2 patients) and could be ameliorated by slowing the infusion rate or by discontinuing the drug (one patient). Iloprost appears to be safe and effective for relieving the symptoms of diabetic neuropathy. Our results provide the rationale for a double-blind, clinical trial in larger populations of diabetics with peripheral neuropathy.

Hemodynamic, platelet and clinical responses to prostacyclin in unstable angina pectoris

The hemodynamic and platelet effects of prostacyclin (PGI2) were investigated in 27 patients with unstable angina (14 treated patients; 13 control subjects) given a 72-hour infusion (5 ng/kg/min) or placebo. This randomized study was double-blind and conducted as a substudy of a multicenter trial testing the clinical efficacy of PGI2. The clinical and angiographic features were identical in the 2 groups. Blood pressure and heart rate were not modified significantly by PGI2. A recurrence of angina during infusion occurred in 8 treated patients (57.1%) and in 8 control subjects (61.5%). Two patients receiving PGI2 and none in the control group developed a myocardial infarction. Levels of 6-keto-prostaglandin F1 alpha, a stable metabolite of PGI2, increased from baseline values (less than 20 pg/ml) to 605 +/- 41 pg/ml during infusion. Levels of fibrinopeptide A, beta-thromboglobulin, platelet factor 4, thromboxane B2 and the platelet aggregates ratio in blood were similar between the 2 groups before, during and after PGI2 infusion. Prostacyclin reduced ex vivo platelet aggregation to adenosine diphosphate and thromboxane B2 generation by approximately 50% during the infusion period with return of aggregation to baseline and platelet thromboxane B2 production to above baseline after the discontinuation of PGI2. Thus, despite favorable effects of PGI2 upon platelet aggregation and systemic hemodynamics, the prostanoid failed to improve the clinical evolution of unstable angina.

Beneficial effects of iloprost in the stunned canine myocardium

The effect of the prostacyclin-mimetic, iloprost, on the reversibly damaged ("stunned") myocardium was studied in barbital-anesthetized, open-chest dogs subjected to 15 minutes of coronary artery occlusion and 3 hours of reperfusion. Regional myocardial segment shortening (%SS) was measured in the subendocardium of nonischemic and ischemic-reperfused areas by sonomicrometry. Iloprost was infused for 30 minutes beginning 15 minutes prior to occlusion (0.05 microgram/kg/min, ILO-LOW, or 0.1 microgram/kg/min, ILO-HIGH) or immediately prior to reperfusion (0.1 microgram/kg/min, ILO-REP). %SS in the ischemic-reperfused region recovered to 3% of pretreatment values in the control (saline-treated) group by 3 hours of reperfusion. In contrast, %SS in the iloprost-treated groups was significantly enhanced versus the control group at all times of reperfusion. At 3 hours of reperfusion, %SS recovered to 43% (ILO-LOW), 58% (ILO-HIGH), and 35% (ILO-REP) of pretreatment values. The beneficial effect on functional recovery was significantly greater when iloprost was administered before occlusion versus immediately prior to reperfusion. Thus, part of the salutory effects of iloprost appear to occur prior to and/or during ischemia. Iloprost did not improve collateral blood flow to the ischemic region or myocardial high energy phosphate content at 3 hours of reperfusion. While iloprost significantly decreased mean arterial pressure during ischemia and early reperfusion, the hypotensive action did not appear to play a role in the amelioration of postischemic dysfunction, as preocclusion treatment with an equihypotensive dose of sodium nitroprusside produced no significant effect on postischemic recovery beyond 5 minutes of reperfusion. Results of in vitro experiments indicated that iloprost had no effect on the xanthine oxidase free-radical generating system including lipid peroxidation. However, iloprost decreased the neutrophil-derived superoxide burst after chemotactic stimulation. This beneficial action may, in part, explain the efficacy of iloprost in enhancing postischemic function of the stunned myocardium.

Platelets and antiplatelet therapy in ischemic heart disease

Blood platelets have been shown to play an important role not only in thrombosis, but also in the pathogenesis of coronary artery disease and its complications. Drugs that affect platelets have been shown to reduce mortality in survivors of acute myocardial infarction, to reduce the risk of myocardial infarction in patients with unstable angina, and to preserve the potency of saphenous venous grafts used to bypass obstructed coronary arteries. The drugs may also play a role in the primary prevention of arteriosclerosis and in preventing thrombotic complications following coronary angioplasty.

Effects of iloprost (ZK 36374), a prostacyclin derivative, on platelet function after ischaemic exercise in patients with stable angina pectoris

The effect of a chemically stable prostacyclin analogue (Iloprost) on platelet function was investigated in a controlled study in patients with angiographically confirmed stable angina pectoris after ischaemic exercise. In placebo experiments, ADP platelet aggregation was increased after exercise only when measured in whole blood and not in PRP. While plasma thromboxane B2 levels were unchanged, those of 6-keto PGF1 alpha were significantly although transiently increased after exercise. Iloprost displayed a potent antiaggregating activity in PRP and also reversed platelet hyperaggregation occurring in whole blood determinations after exercise. Plasma thromboxane B2 levels were significantly reduced but occasionally a rebound increase occurred 30 min. after end of the infusion. In contrast plasma level of 6-keto PGF1 alpha did not change after Iloprost and its recorded post-exercise increase was counteracted, thus suggesting a negative feed-back mechanism between Iloprost and natural prostacyclin. The data also suggest that degradation of the analogue is probably accomplished through pathways different from those of PGI2.

Eicosanoids and myocardial ischaemia

The available data clearly suggest large alterations in myocardial eicosanoid generation during myocardial ischaemia and demonstrate important actions of eicosanoids on myocardial function during ischaemic conditions. These actions include direct effects on the injured myocardium as well as influences on other target cells, such as platelets and leukocytes. Selective modifications of eicosanoid generation, for example by providing exogenous PGI2 or by inhibiting oxygen toxicity are most challenging approaches for the design of new and potentially valuable cardioprotective agents. Antagonism of thromboxane formation and/or action might be of some value in ischaemia but appears to be less important for reperfusion injury. Leukotrienes and other noncyclic fatty acid peroxidation products are another group of potentially deleterious agents and there is a definite need for more selective inhibitors of leukotriene formation and/or action to establish their role in ischaemia.