[Experimental study of the effect of pentaerythritol tetranitrate in acute myocardial infarct]

Pentaerithrityltetranitrate (PETN) is an organic nitrate ester with high selectivity to venous vessels and little development of tolerance. Here we report experimental results concerning the hemodynamic and antiischemic effects of intravenously administered PETN. The experiments were performed with anesthetized, open-chest minipigs (25 to 35 kg body weight [bw]). PETN (0.125, 0.25, 0.5 mg/kg bw, i.v.) dose-dependently decreased left ventricular systolic pressure without change in peripheral vascular resistance. A reflex increase in heart rate returned to normal within 20 minutes (0.125 and 0.25 mg/kg). PETN (0.5 mg/kg) also transiently (10 minutes) decreased left ventricular contractility. In additional experiments, myocardial infarction was induced by LAD occlusion (1 hour), followed by reperfusion (3 hours). PETN (0.6 mg/h, i.v.) was administered starting 20 minutes before ischemia until the end of reperfusion. While PETN did not cause hemodynamic changes, infarct size was significantly decreased compared with vehicle (56 +/- 6% vs 83 +/- 3% of area at risk, p < 0.05). Regional contractile function (ultrasound crystals) was completely abolished during ischemia and did not recover during 3 hours reperfusion in control hearts. However, PETN-treated pigs showed partial functional recovery (19 +/- 5%, p < 0.05 vs vehicle) during the first hour of reperfusion. Histologic evaluation revealed a decreased number of granulocytes accumulated in the ischemic myocardium of PETN-treated animals. Accordingly, in-vitro experiments showed a reduction by PETN of the adherence of HL-60 cells differentiated to granulocytes to vascular smooth muscle cells. Therefore, PETN reduced infarct size and improved myocardial function after LAD occlusion and reperfusion. It is concluded that the intravenous administration of PETN might be of advantage in the treatment of acute myocardial ischemia.

Influence of mycophenolic acid and FK-506 on human platelet activation in vitro

BACKGROUND/AIM

FK-506 (FK) and mycophenolic acid (MPA) are immunosuppressive agents used in kidney transplant recipients. Their effect on posttransplant thromboembolic complications is either controversial (FK) or has not been described (MPA). Thromboembolic events are among the consequences of platelet hyperaggregability which can be identified by measuring platelet aggregation. The aim of this study was to evaluate the in vitro effects of MPA and FK upon platelet activation in healthy subjects.

METHODS

Platelet-rich plasma from healthy volunteers (n = 18) was incubated with FK (70 ng/ml), FK vehicle, and MPA (30 microg/ml) before platelet aggregation was induced by the platelet agonists adenosine diphosphate (2 and 5 microM) and collagen 0.5 and 1.0 microg/ml). Aggregation was measured by recording the optical density.

RESULTS

MPA resulted in a significant decrease in the platelet response to collagen (1.0 microg/ml) in platelet-rich plasma, whereas FK significantly increased platelet aggregation in response to collagen (0.5 microg/ml). The vehicle of FK had no influence on platelet aggregation with either agonist.

CONCLUSIONS

The decreased platelet-activating response following preincubation with MPA may favor its use in kidney transplant recipients to reduce thromboembolic events. The FK-induced enhancement of platelet aggregation shown in vitro may lead to thromboembolic complications in transplant recipients.

Habitual smoking causes an abnormality in platelet thromboxane A2 metabolism and results in an altered susceptibility to aspirin effects

The present study investigates the effects of aspirin (100 mg every second day for 14 days) on platelet function in nine healthy non-smokers and in nine healthy habitual smokers. There was a significantly (P < 0.05) stronger inhibition of collagen (0.6 microgram/ml)- and ADP (2 microM)-induced platelet aggregation by aspirin in smokers as compared to non-smokers. This difference occurred in the presence of an almost complete (> 95%) inhibition of thromboxane A2 (TXA2) synthesis in both groups. The platelet capacity to generate TXA2 in vitro was significantly reduced in smokers, urinary excretion of TXA2, however, was significantly increased. Thus, the better susceptibility of smokers to anti-aggregatory effects of aspirin is very likely to be related to a chronic smoking-induced alteration of platelet TXA2 system. Cessation of smoking should, therefore, be encouraged.

Improvement of epidermal adhesion by surface modification of craniofacial abutments

Craniofacial implants may present peri-implant inflammation because there is no close adhesion of the epithelium to abutments and because of bacteria infiltrating the subcutaneous tissue through the gap. Therefore an attempt was made to improve adhesion of epithelium to abutments. In an in vitro model, adhesion of epithelial cells (HaCat cells) to nonmodified and 3 modified Brånemark System abutment surfaces was quantified. It was found that more cells were adherent in sequence at silicone-coated surfaces, sandblasted surfaces, and collagen-coated (Types I and IV) surfaces than on nonmodified abutments. It was concluded that it is possible to improve epidermal adhesion to abutments through modification of abutment surfaces.

Reduction of infarct size by selective stimulation of prostaglandin EP(3)receptors in the reperfused ischemic pig heart

We have previously identified prostaglandin EP(3)receptors in left ventricular myocardium. To assess the potential contribution of this receptor subtype to the anti-ischemic properties of E-type prostaglandins (i.e. PGE(1)), two groups of anesthetized open-chest minipigs were subjected to LAD occlusion (1 h) and reperfusion (3 h). In one group, the selective EP(3)receptor agonist M&B 28.767 (2 pmol/kgxmin) was infused into the LAD from 20 min before ischemia until the end of reperfusion. The other group received vehicle. M&B 28.767 did not alter the systemic hemodynamics, but significantly reduced infarct size (tetrazolium staining) and creatine kinase release by 53% and 48%, respectively. Ischemia-induced ventricular arrhythmias were mostly reduced. Further experiments analysed the effects of EP(3)receptor stimulation on normoxic myocardium. PGE(1), an unselective agonist to all EP receptor subtypes, as well as M&B 28.767 (2 pmol/kgxmin of each into the LAD) reduced the action potential duration (epicardial monophasic electrodes) and almost prevented the inotropic response to intravenous isoprenaline. This dual response is consistent with the EP(3)receptor coupling to an inhibitory G protein. This was confirmed in separate experiments with stable Chinese hamster ovary cell transfectants expressing the porcine EP(3)receptor, where M&B 28.767 inhibited the forskolin-induced increase in cAMP in a concentration-dependent manner. It is concluded that the protection of reperfused ischemic myocardium by E-type prostaglandins is mediated by EP(3)receptors, which seems to involve a combined activation of repolarizing membrane currents and an inhibition of deleterious effects caused by ischemia-induced catecholamine release.

Analysis of a porcine EP3-receptor: cloning, expression and signal transduction

A cDNA clone, encoding a complete porcine EP3 receptor, was isolated from a porcine heart cDNA library. The deduced amino acid sequence revealed a protein of 387 amino acid residues with an estimated molecular weight of 43 kD and strongest homology to the human EP3-II receptor (84% identity on protein level). Ligand binding studies with transfected COS-7 cells, expressing the porcine receptor, showed displacement of [3H]PGE1 with the EP3-specific agonist M&B 28.767, the EP1/EP3-agonist sulprostone but not with the EP2-specific agonist butaprost. Stimulation of transfected CHO cells with M&B 28.767 resulted in inhibition of forskolin-induced cAMP formation, suggesting coupling to an inhibitory G protein. Agonist-induced translocation of the transcription factor NFkappaB into the nucleus of transfected CHO cells was demonstrated by Western blot analysis, indicating that these EP3 receptors modulate NFkappaB-dependent cellular signal transduction. Analysis of the genomic organization identified the major transcription initiation site at about 160 bp upstream of the ATG start codon. The 800-bp 5' flanking region contains a variety of putative cis-acting regulatory elements, including binding sites for AP2, SP1 and MyoD (E-box). The present data will now allow further studies on EP3 receptor-mediated signal transduction and its regulation.

Azetylsalizylsäure und Thromboxaninhibitoren

Azetylsalizylsäure (ASA) ist seit über 100 Jahren Standardtherapeutikum zur Behandlung von Schmerzen und Entzündungen und seit etwa 40 Jahren Standardsubstanz als Plättchenfunktionshemmer. Grundlage dieser vielfältigen Wirkungen von ASA ist die Hemmung der Fettsäure-Cyclooxygenase (COX). Diese beruht auf einer irreversiblen Acetylierung des Serin 530 im Cyclooxygenasemolekül und nachfolgender sterischer Hinderung des Zutritts des Substrates Arachidonsäure zum katalytischen Zentrum des Enzyms. Die Antiplättchenwirkung von ASA beinhaltet ausschließlich eine Hemmung der thrombozytären Thromboxansynthese nach Inhibition der COX-1. Andere Mechanismen der Plättchenaktivierung werden nicht beeinflußt. Nebenwirkungen von ASA, z. B. Magen-Darm-Blutungen, werden ebenfalls entscheidend durch die Hemmung der Prostaglandinsynthese bestimmt. Daher wurde versucht, eine selektive Hemmung der Thromboxansynthese, Blockade von Thromboxanrezeptoren oder beides zu erreichen. Dazoxiben, Picotamide und Terbogrel sind Referenzsubstanzen für diese Entwicklungen. Die vorliegenden klinischen Daten für Dazoxiben sind weniger überzeugend, für Picotamid wurde bei Patienten mit peripherer Verschlußkrankheit eine nur tendenzielle Senkung der Reverschlußrate gezeigt. Eine größere klinische Studie mit dem kombinierten Inhibitor Terbogrel ist derzeit in Vorbereitung. Insgesamt wird ASA seinen Stellenwert als Basistherapeutikum zur Verhinderung thromboembolischer Gefäßverschlüsse sicher behalten, wobei neuere Antiplättchensubstanzen wie Abciximab bei schweren akuten Koronarsyndromen oder eine Kombination mit Thienopyridinen bei akuten Koronarinterventionen die Wirkung verstärkt. Der therapeutische Stellenwert von selektiven Thromboxaninhibitoren in der antithrombotischen Therapie ist noch zu definieren.

Acetylsalicylic acid enhances arrhythmogeneity in a model of local ischemia of isolated rabbit hearts

Acetylsalicylic acid often is used in the treatment and prophylaxis of regional myocardial ischemia and infarction. However, only little is known about its electrophysiological effects and on possible proarrhythmic effects of the drug. Thus, the aim of this study was to evaluate the electrophysiological effects of acetylsalicylic acid in normal isolated saline perfused rabbit hearts and in hearts submitted to regional ischemia. Isolated saline perfused rabbit hearts were treated with increasing concentrations of acetylsalicylic acid (0.05, 0.1, 0.5 and 1 microM). The epicardial activation and repolarisation process were analysed using an epicardial mapping (256 unipolar leads). Activation and repolarisation time were determined for each electrode from which data the 'breakthrough-points' of epicardial activation were determined. At each electrode an activation vector was calculated giving the direction and velocity of the local excitation wave. The similarity of selected heart beats compared to the control was evaluated by determination of the percentage of identical breakthrough-points and of similar vectors (deviation < or = 5 degrees). At each electrode the local epicardial action potential duration was assessed as the activation recovery interval and the standard deviation of the epicardial action potential duration (of 256 leads, = dispersion) was determined. In a second series of experiments 30 min regional ischemia was induced by occlusion of the left descendent coronary artery followed by 30 min reperfusion in the absence or presence of 0.5 microM acetylsalicylic acid or 1 micro/M indomethacin. The degree of ischemia was assessed by the reduction in coronary flow, by the degree of ST-elevation and by the area in which ST-elevation was registered. Under non-ischemic conditions acetylsalicylic acid led to an increase in the epicardial action potential duration (7%), a decrease in the breakthrough-point similarity (by 10%) and vectorfield similarity (by 15%). In control hearts submitted to regional ischemia the similarity of the vectorfields and of the breakthrough-points, as well as the duration of the epicardial action potentials were markedly reduced while the dispersion was greatly increased. In the ischemic region there was a significant ST-deviation from the isoelectrical line. These changes of ST-segments were significantly enhanced by 0.5 microM acetylsalicylic acid, so that in all (7/7) acetylsalicylic acid treated hearts sustained ventricular fibrillation occurred after 20 min ischemia, whereas in the absence of acetylsalicylic acid fibrillation was found in only 2/7 hearts during reperfusion and not during ischemia. 1 microM indomethacin did not cause these changes. In all ischemia/reperfusion series of experiments the reduction in coronary flow and left ventricular pressure by ischemia was of the same degree and we did not observe significant differences in the size of ischemic area. Using 14C-acetylsalicylic acid, an accumulation of acetylsalicylic acid in the ischemic region could be observed. From these results we conclude, that acetylsalicylic acid can induce ventricular fibrillation. Thus, in acute myocardial ischemia, acetylsalicylic acid may have (besides the well known and desired antiaggregatory effects) electrophysiologic side effects which seem to be proarrhythmic in regional ischemia at least in this model.

Expression, function, and regulation of E-type prostaglandin receptors (EP3) in the nonischemic and ischemic pig heart

The action of prostacyclin, prostaglandin E1 (PGE1), and their mimetics on myocardial function includes changes in contractility, electrophysiological properties, and protection from injury caused by transient myocardial ischemia. This study was undertaken to investigate the basic properties of myocardial E-type prostaglandin (EP) receptors. Ligand binding studies using an enriched preparation of sarcolemmal membranes prepared from pig hearts revealed a single class of binding sites for [3H]PGE1, with a Kd of 3.7 nmol/L and a Bmax of 92 fmol/mg protein. Competition experiments indicated highest affinity for EPs, suggesting an EP receptor. In addition, the EP receptor subtype-selective agonists sulprostone (EP1 and EP3) and M&B 28.767 (EP3) were active, suggesting the presence of an EP3 receptor subtype. PGE1 stimulated sarcolemmal GTPase and inhibited sarcolemmal adenylyl cyclase activity, indicating EP3 receptor coupling to an inhibitory G protein (Gi). Additional in vivo experiments showed that intracoronary infusion of PGE1 (1 nmol/min) decreased isoprenaline-stimulated left ventricular contractile activity without altering systemic vascular resistance. This inhibition of beta-adrenergic effects is compatible with the known myocardial anti-ischemic action of prostaglandins. Further experiments examined EP3 receptor density and G-protein coupling in sarcolemma from ischemic and reperfused ischemic myocardium. In anesthetized open-chest minipigs, occlusion of the left anterior descending coronary artery for 60 minutes increased EP3 receptor density by 50%, whereas receptor affinity was unchanged. This upregulation was prevented by pretreatment with colchicine (2 mg/kg i.v.), indicating microtubule-dependent receptor externalization. Northern hybridization showed comparable EP3 receptor mRNA expression in control and ischemic myocardium. The increase of receptor protein was reversed during 60 minutes of reperfusion. G-protein coupling proved to be intact in ischemic and reperfused ischemic myocardial tissue, as shown by preserved GTP-gamma-S-induced decrease of [3H]PGE1 binding. These data demonstrate for the first time that myocardial receptors for PGE1 belong to the EP3 subtype. The properties of this receptor include inhibition of adenylyl cyclase and upregulation during regional myocardial ischemia, suggesting an involvement in the anti-ischemic activity of E- and I-type prostaglandins.

Platelet PGI2 receptor affinity is reduced in pre-eclampsia

Prostacyclin (PGI2) receptors were studied in platelet membrane preparations from women with normal pregnancy, pregnancy-induced hypertension (PIH) or pre-eclampsia. Patient groups showed no differences in gestational week at delivery. A markedly lower birth weight, however, was found in pre-eclampsia. No differences between groups could be detected in platelet PGI2 receptor number. In contrast, the binding affinity to the PGI2 mimetic iloprost was considerably reduced in pre-eclampsia, whereas receptor affinity between PIH and normal pregnancy did not differ significantly.

[Thrombocyte prostacyclin receptors in gestational hypertension and pre-eclampsia]

OBJECTIVE

To determine prostacyclin (PGI2) receptor characteristics in pregnancies complicated by hypertension and to assess any relation to the clinical outcome.

METHODS

Radioligand binding studies with [3H]-Iloprost were performed to measure receptor capacity (Bmax) and affinity (Kd-1) using platelet membranes from patients with preeclampsia, gestational hypertension or normal pregnancy.

RESULTS

PGI2 receptor capacity did not differ between the patient groups. In contrast, PGI2 receptor affinity was diminished in gestational hypertension and considerably reduced in preeclampsia compared to normal pregnancy. A similar pattern was found in fetal growth (normal pregnancy > gestational hypertension > preeclampsia). Furthermore, the rate of low Apgar scores and acidosis was increased in preeclampsia.

CONCLUSIONS

In preeclampsia reduced platelet PGI2 receptor affinity was found as well as poor pregnancy outcome in comparison with normal pregnancy, whereas these differences were less pronounced in gestational hypertension. This suggests a role of PGI2 and its receptor in gestational hypertension and in particular in preeclampsia.

The contribution of tumour necrosis factor-alpha and endothelin-1 to the increase of coronary resistance in hearts from rats treated with endotoxin

1. Inflammatory disease states predispose to myocardial infarction. Here we have investigated the effects of a systemic inflammatory response syndrome, i.e. lipopolysaccharide (LPS)-induced circulatory shock in rats, on coronary vascular tone. 2. Anaesthetized rats were given LPS (10 mg kg-1, i.v.) and the hearts excised 180 min later for isolated perfusion at constant flow by the Langendorff technique. Once the ex vivo perfusion was started, the perfusion pressure strongly increased in these hearts compared to hearts from control rats (130 +/- 3 vs. 49 +/- 3 mmHg after 10 min). This increase in coronary resistance was not associated with a reduction in endothelial cell function, for the vasodilator responses to bradykinin were unchanged. 3. When hearts were removed 30 min after the injection of LPS, the LPS-induced rise in perfusion pressure was delayed. No changes in perfusion pressure were seen when the hearts were removed 15 min after the injection of LPS. Pre-treatment with cycloheximide or an anti-tumour necrosis factor-alpha (TNF-alpha) antibody or continuous infusion in vivo and in vitro of the endothelin ETA receptor selective antagonist FR 139317, greatly decreased the increase in coronary vascular resistance induced by LPS. 4. These data suggest that TNF-alpha may induce the release of endothelin-1 (ET-1) and that this mediates at least part of the coronary vasoconstriction. This hypothesis is supported by the demonstration that LPS administration increased the circulating levels of both TNF-alpha and ET-1. 5. We conclude, therefore, that in inflammatory disease states, such as LPS-induced septic shock, there is the sequential release of TNF-alpha and endothelin-1 which leads to an increase in coronary vascular tone and so a predisposition to myocardial ischaemia. Inactivation of TNF-alpha by an antibody as well as ETA receptor blockade by a selective antagonist may effectively interfere with this pathway.

Antiatherosclerotic effects of oral naftidrofuryl in cholesterol-fed rabbits involve inhibition of neutrophil function

We investigated the action of oral naftidrofuryl, a serotonin (5-HT2)antagonist, on atheromatous plaque formation, endothelial function, and neutrophil activity in cholesterol-fed (1% for 12 weeks) rabbits. Cholesterol feeding caused almost complete (84 +/- 4%) coverage of the aortic surface with atheromas and a marked intimal thickening. The endothelium-dependent relaxation to acetylcholine (ACh 1 nM-10 microM) and substance P (30 nM) was considerably reduced, whereas the relaxing effect to the endothelium-independent nitric oxide donor linsidomine (SIN-1) (100 microM) was unchanged. Treatment of hypercholesterolemic rabbits with naftidrofuryl (50 mg/kg body weight) resulted in a marked (54 +/- 6%, p < 0.05) reduction in aortic plaque formation. Endothelium-dependent relaxation to ACh was significantly improved in rings of both thoracic aorta: 33 +/- 5 versus 14 +/- 5% (p < 0.05) and abdominal aorta 68 +/- 9 versus 37 +/- 10% (p < 0.05). Similar results were obtained with substance P, but the responses to SIN-1 were unchanged. Zymosan-induced, luminol-enhanced chemiluminescence of polymorphonuclear leukocytes (PMN) was markedly stimulated in cholesterol-fed rabbits. Naftidrofuryl reduced this hyperreactivity to that of control rabbits. There was no change by naftidrofuryl in any of these parameters in control rabbits, precluding a direct action of the compound in nonhypercholesterolemic conditions. These data demonstrate significant endothelium-protective actions of long-term oral naftidrofuryl in cholesterol-fed rabbits that involve inhibition of cholesterol-induced neutrophil activation.

Endothelin 1 mediates ex vivo coronary vasoconstriction caused by exogenous and endogenous cytokines

Treatment of rats with cytokines has been associated with an increase in the circulating levels of endothelin 1 (ET-1). Here we show that administration of tumor necrosis factor alpha (TNF-alpha; 4 micrograms.kg-1) to anesthetized rats caused within 15 min a strong elevation in the circulating levels of ET-1. This was associated with a striking coronary vasoconstriction in hearts from these animals when they were removed and perfused in vitro by the Langendorff technique. This vasoconstriction was largely overcome by treatment with either the endothelin type A (ETA) receptor antagonist FR 139317 or antibody against ET-1. Furthermore, it was mimicked by in vivo exposure to exogenous ET-1. Endogenously produced TNF-alpha may also cause such a coronary vasoconstriction, for treatment with interleukin 2 (600 micrograms.kg-1) produced an increase in coronary perfusion pressure that correlated with the increases in circulating TNF-alpha. This coronary vasoconstriction was substantially reversed by treatment either with antibody against TNF-alpha or with FR 139317. We suggest, therefore, that cytokine-driven changes in the production of ET-1 are key events in the development of vascular pathologies.

Regulation of prostaglandin receptors in myocardial ischemia

Sarcolemmal membranes from pig hearts express a homogenous class of binding sites for [3H]PGE1. Competition binding studies with EP receptor suptype selective ligands suggest an EP3 receptor subtype. The GTP analogue GTP gamma S reduced affinity without changing binding capacity, indicating a G protein coupled EP3 receptor. Regional myocardial ischemia (60 min) in anesthetized, open-chest pigs caused a 50% increase of the number of binding sites while GTP gamma S still decreased [3H]PGE1 binding, suggesting intact G protein coupling. Myocardial ischemia may, therefore, modify myocardial actions of prostaglandins.

Protection of reperfused ischemic pig myocardium by nexopamil, a new combined Ca2+ and serotonin antagonist

We investigated the ability of a newly developed calcium and serotonin (5-HT2) antagonist, nexopamil, to protect the heart from ischemia- and reperfusion-induced myocardial injury. Anesthetized open-chest minipigs were subjected to 1 h left anterior descending coronary artery (LAD) occlusion and 3-h reperfusion. Thirty minutes before occlusion, one group of pigs (n = 7) received nexopamil (0.1 mg/kg intravenously, i.v.) and another group (n = 9) received vehicle. Nexopamil reduced infarct size (IS: tetrazolium stain) from 47 +/- 4% (vehicle) to 21 +/- 7% of the ischemic area (p < 0.05). In nexopamil-treated pigs, this was paralleled by reduced release of creatine kinase (CK) into coronary venous blood. In addition, nexopamil prevented reperfusion-associated myocardial contracture. Nexopamil decreased left ventricular peak pressure (LVPP) and pressure rate index (PRI) immediately before coronary occlusion by 11 and 18%, respectively. Coadministration of methoxamine (2 mg/kg, n = 6) with nexopamil increased LVPP and PRI to values of vehicle-treated pigs but did not prevent reduction in infarct size or CK activity in plasma. During reperfusion, neutrophil granulocytes showed increased formation of reactive oxygen metabolites (chemiluminescence) after stimulation with zymosan. Neutrophil counts in coronary venous blood were significantly reduced at 3 h reperfusion. Both changes were attenuated in nexopamil-treated pigs. Coronary occlusion resulted in increased platelet reactivity in coronary venous blood (collagen-induced aggregation) that was prevented by nexopamil. Nexopamil significantly increased the transcardiac (coronary venous-arterial) concentration gradients of 6-oxo-prostaglandin F1 alpha (PGF1 alpha) without changing thromboxane (B2 (TBX2) concentrations, indicating a selective increase in cardiocoronary PGI2 formation. Nexopamil reduces myocardial injury in reperfused ischemic myocardium. Besides calcium channel blocking activity, inhibition of ischemia-induced neutrophil activation and enhanced endogenous PGI2 formation may be factors contributing to the beneficial effects of nexopamil.

Antiplatelet effects of ticlopidine are reduced in experimental hypercholesterolemia

This study determines the antiplatelet effects of oral ticlopidine (100 mg/kg x day) in experimental hypercholesterolemia. Rabbits were fed either a standard diet or a cholesterol-enriched diet (0.5% for 3 months, 1% for 1 month). In normocholesterolemic controls ADP-, but not collagen-induced platelet aggregation was inhibited by ticlopidine treatment. This was accompanied by a significantly enhanced inhibition of ADP-induced platelet aggregation and stimulation of cyclic AMP accumulation by iloprost. Hypercholesterolemia considerably attenuated the inhibition of ADP-induced aggregation by ticlopidine but did not change its effect on the iloprost-induced inhibition of platelet function and cyclic AMP formation. ADP-induced platelet-derived thromboxane formation was considerably greater in hypercholesterolemic rabbits and not reduced by ticlopidine. Ticlopidine did also not significantly influence the extent and severity of atherosclerotic plaque formation although a tendency for improvement was observed in a subgroup of animals. The data suggest that hypercholesterolemia attenuates the inhibitory effect of ticlopidine on ADP-induced platelet aggregation. This might be related to the stimulation of thromboxane formation by ADP in hypercholesterolemia. The maintained protection from ADP-induced inhibition of cAMP accumulation suggests a minor role of this mechanism in the progression of hypercholesterolemia-induced vessel disease in this model.

The actions of lovastatin on platelet function and platelet eicosanoid receptors in type II hypercholesterolaemia. A double-blind, placebo-controlled, prospective study

We have studied the effects of 12 weeks of lovastatin (20 mg per day) on platelet function and thromboxane formation in 18 patients with type II hypercholesterolaemia in a double-blind, placebo-controlled, prospective study. Lovastatin significantly reduced total serum and LDL-cholesterol by 20% and 25% respectively. Washed platelets of lovastatin-treated patients had significantly reduced collagen-induced aggregation and thromboxane formation ex vivo. There was no change in ADP-induced platelet aggregation, but a significant increase in prostacyclin (iloprost)-stimulated platelet cyclic AMP concentrations in lovastatin-treated patients. This was associated with a significant increase in the number of prostacyclin receptors in platelet membranes prepared from lovastatin-treated patients. There was also an increase in platelet thromboxane receptors. There were no such changes in the placebo group. These data confirm our original observation of normalization of platelet function in hypercholesterolaemia by HMGCoA reductase inhibitors and suggest changes in platelet membrane composition at the megakaryocyte level as a possible site of action.

Antiatherosclerotic effects of oral cicaprost in experimental hypercholesterolemia in rabbits

The efficacy of the oral prostacyclin mimetic cicaprost in preventing atheromatous plaque formation was studied in an in vivo model of experimental hypercholesterolemia. New Zealand white rabbits were fed either standard chow or a cholesterol-enriched (1%) diet for 12 weeks. Cicaprost was added to the drinking water in a non-hypotensive dose (5 micrograms/kg/day) and withdrawn 3 days prior to studying platelet, leukocyte and endothelial function. In cholesterol-fed rabbits, oral cicaprost reduced the aortic intimal surface covered by atheromatous lesions from 84 to 63% (P < 0.05). There was no major difference in serum lipid composition between cicaprost- and vehicle-treated animals. In hyper-cholesterolemic rabbits there was a significant impairment of endothelium-dependent relaxations. Cicaprost treatment considerably improved this endothelial function but had no effect in rabbits receiving standard diet. In addition, platelet and leukocyte hyperreactivity, as seen in hypercholesterolemic rabbits, were largely reduced by cicaprost treatment. These data are the first to demonstrate marked antiatherosclerotic effects of long-term oral prostacyclin treatment. The mechanism may be related to improved endothelial function and subsequent prevention of secondary platelet and neutrophil hyperreactivity.

Oral naftidrofuryl prevents platelet hyperreactivity ex vivo and inhibits functional desensitization to prostacyclin in hypercholesterolemic rabbits

Among other mediators, platelet-derived serotonin (5-HT) may contribute to thromboembolic complications of atherosclerosis. We determined whether long-term oral treatment with the 5-HT2 antagonist naftidrofuryl (NAF, 50 mg/kg daily for 12 weeks) alters platelet function in cholesterol-fed (1%) rabbits. Hypercholesterolemia resulted in marked platelet hyperreactivity to collagen and ADP. This included increased aggregation, ATP secretion, and thromboxane formation; e.g., collagen-induced (1.2 micrograms/ml) platelet aggregation was stimulated to 210 +/- 10 mm/30 s in cholesterol-fed rabbits as compared with 108 +/- 9 mm/30 s in rabbits fed a standard diet (p < 0.05). Inhibition of ADP-stimulated platelet activation by the prostacyclin mimetic iloprost was significantly reduced. NAF did not reduce plasma cholesterol in hypercholesterolemia, but prevented enhanced platelet aggregation, thromboxane formation, and ATP secretion. NAF treatment significantly reduced collagen-induced (1.2 micrograms/ml) aggregation to 81 +/- 20 mm/30 s in these animals (p < 0.05). NAF also inhibited functional desensitization of platelets to iloprost, but did not alter the impaired binding of [3H]iloprost to platelet membranes in hypercholesterolemic animals. NAF also did not change any of these parameters in normocholesterolemic rabbits. These data suggest beneficial effects of NAF on platelet hyperreactivity in experimental hypercholesterolemia which may also be relevant for its clinical use.