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Background: The transcription factor E2F-1 promotes S-phase entry and death in transformed cells and primary cardiomyocytes. We tested the hypothesis that overexpression of E2F-1 forces growth-arrested human coronary vascular smooth muscle cells (VSMCs) to enter the S phase, undergo apoptosis, and thereby regulate VSMC growth., Methods and Results: Early-passage (8 times., Conclusions: Overexpression of the transcription factor E2F-1 regulates growth of human coronary VSMCs by forcing the cells to enter the S phase and then to die. Cell death appears to involve caspase 3-like activity, which, in the VSMCs, is markedly increased by overexpression of E2F-1.

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a potent phospholipid mediator of numerous inflammatory and thrombotic responses. The purpose of this study was to determine if PAF synthesis is elevated in damaged coronary arteries after a sustained period of cyclic flow variation (CFV), a phenomenon caused by alternating periods of thrombosis and reperfusion at sites of endothelial injury. Cyclic flow was established and maintained in the left anterior descending coronary arteries (LADs) of 10 dogs. After 8 hours of CFV, the section of damaged LAD containing the thrombus and control sections of the circumflex artery, carotid artery, and saphenous vein was excised, and the total lipids were extracted. The PAF was then purified by silica column chromatography and high-performance liquid chromatography and assayed by both a rabbit platelet bioassay and a PAF radioimmunoassay. With the platelet bioassay, PAF levels of 8.9 +/- 4.0 (range, 4.8 to 15.5) pg/mg wet wt were found in the damaged LADs from the 10 dogs. This PAF bioactivity was completely inhibited by a PAF receptor antagonist. When the radioimmunoassay was used, slightly higher PAF levels of 16.3 +/- 12.9 (range, 4.5 to 41.8) pg/mg wet wt were observed in the LADs. Overall, these PAF levels were 3- to 64-fold higher than in the control vessels when either assay method was used. Although increases in PAF were observed in the damaged LADs, measurements of PAF in blood samples taken from the LAD and the aorta (control) failed to demonstrate any site-specific increase of PAF in the blood. In related experiments, PAF was also measured in 23 endarterectomy samples taken from the coronary arteries of 16 patients with severe atherosclerosis. The PAF levels in these samples were highly variable (2.9 +/- 2.2 [range, 0.3 to 8.5] pg/mg wet wt) and showed no correlation with tissue mass, suggesting that PAF is affected by factors other than the simple presence of atherosclerotic tissue in the vessel. These findings provide direct evidence that PAF is synthesized locally at the site of endothelial injury during thrombosis and that PAF accumulates in the atherosclerotic plaque of some patients with advanced coronary artery disease.

Background: Platelets play an important role in the pathophysiology of acute coronary syndromes. The interaction between the platelet glycoprotein Ib receptor and von Willebrand factor is a critical event allowing platelet adhesion and aggregation and subsequent thrombus formation in vessels with high shear rates and damaged endothelium. Therefore, we tested the hypotheses that VCL, an antagonist of von Willebrand-glycoprotein Ib binding domain, (1) attenuates/abolishes cyclic flow variations in stenosed, endothelium-injured coronary arteries in nonhuman primates and (2) reduces botrocetin-induced platelet aggregation in vitro after intravenous in vivo administration., Methods and Results: Cyclic flow variations were established in anesthetized, open-chest baboons (n = 18). The baboons were divided into three groups. One group (n = 8) received a bolus of VCL (4 mg/kg IV) followed by an infusion (6 mg.kg-1.h-1) for 90 minutes (schedule A). Another group (n = 6) received a 2-mg/kg bolus followed by an infusion of 3 mg.kg-1.h-1 for 90 minutes (schedule B). The third group received a placebo infusion of normal saline. Under dosing schedule A, cyclic flow variations were abolished in 7 of 8 baboons after 33 +/- 18 minutes and markedly attenuated in 1. The frequency of cyclic flow variations fell from 18 +/- 9.4 per hour during the control period to 1 +/- 2.5 per hour after VCL infusion, P < .002. After cessation of infusion, cyclic flow variations remained abolished in 5 of 7 animals for > 3 hours and returned in 2 of 7 after 2 to 2.5 hours. Under schedule B, cyclic flow variations were abolished in 3 of 6 baboons and markedly reduced in the remainder. The number of cyclic flow variations fell from 17 +/- 4.8 per hour during the control period to 5 +/- 4.9 per hour after the VCL infusion, P < .001. The cyclic flow variations returned spontaneously at 38 +/- 40 minutes under this dosing schedule. Placebo infusion of saline had no effect on cyclic flow frequency or severity. VCL administration was associated with slight prolongation in bleeding time and a reduction in botrocetin-induced platelet aggregation. The bleeding time increased from a control time of 88 +/- 32 to 276 +/- 204 seconds, P < .03, and from 142 +/- 28 to 176 +/- 36 seconds, P = .056, for schedules A and B, respectively. VCL decreased platelet aggregation in response to botrocetin (20 micrograms/mL), from a control value of 66 +/- 30.3 to 33 +/- 31.3 omega, P < .05, and from 64 +/- 23.5 to 46 +/- 15.8 omega, P = .006, for dosing schedules A and B, respectively., Conclusions: Therefore, administration of a peptide fragment corresponding to von Willebrand-glycoprotein Ib binding domain (1) is effective in abolishing cyclic flow variations in stenosed, endothelium-injured coronary arteries and (2) reduces platelet aggregation in vivo in response to botrocetin in nonhuman primates.

Background: Prostaglandin E1 is a potent vasodilator with anti-inflammatory and antiplatelet effects. We tested the hypothesis that prostaglandin E1 attenuates or prevents platelet aggregation-associated cyclic flow variations (CFVs) in severely stenosed and endothelium-injured coronary arteries., Methods and Results: We induced CFVs in 21 dogs by placing an external constrictor around the left anterior descending coronary artery at the site where the endothelium had been mechanically injured. The blood flow velocity in the artery was monitored by a pulsed Doppler flow probe. Sixty minutes after CFVs were established, liposome-bound prostaglandin E1, a stable formulation, was administered intravenously to 12 dogs at incremental doses of 0.25, 0.5, 1, and 2 micrograms/kg body wt; it abolished CFVs in 8 of the 12 dogs (67%). After CFVs were eliminated, epinephrine was infused intravenously, and at a dose of 6.6 +/- 1.6 micrograms/min, it restored CFVs in 7 of 7 dogs. Control dogs (n = 9) were treated with free prostaglandin E1, which did not abolish CFVs in any dog., Conclusions: Liposome-bound but not free prostaglandin E1 effectively diminishes CFVs in severely stenosed and endothelium-injured canine coronary arteries.

Background: The efficacy of thrombolytic therapy in treating patients with acute myocardial infarction is limited by failure to achieve reperfusion in some patients, by the prolonged time required to achieve reperfusion, and by reocclusion of some coronary arteries. We designed this study to examine the effect of combined inhibition of thrombin and thromboxane synthesis and blockade of thromboxane A2 receptors in addition to tissue-type plasminogen activator (t-PA) on thrombolysis and reocclusion in an experimental canine model with coronary thrombosis., Methods and Results: Blood flow velocity in the left anterior descending coronary artery (LAD) of 32 anesthetized mongrel dogs was monitored by a pulsed Doppler flow probe. Coronary thrombosis was induced by applying electrical stimulation to the LAD at the site where an external constrictor was used to narrow the artery. Three hours after the formation of occlusive thrombus, animals were randomly assigned to receive one of the following: 1) t-PA (80 micrograms/kg + 8 micrograms.kg-1.min-1 i.v.) and saline; 2) t-PA and hirulog, a hirudin-based synthetic peptide and specific thrombin inhibitor (2 mg/kg + 2 mg.kg-1.hr-1 i.v.); 3) t-PA and ridogrel, a combined thromboxane A2 synthetase inhibitor and receptor antagonist (5 mg/kg + 2.5 mg.kg-1.hr-1 i.v.); or 4) t-PA, hirulog, and ridogrel. Reperfusion developed in 14% (one of seven) of dogs treated with t-PA alone at an average of 86 +/- 4 minutes after treatment, in 78% (seven of nine) of dogs treated with t-PA plus hirulog at 53 +/- 11 minutes, in 13% (one of eight) of dogs treated with t-PA plus ridogrel at 85 +/- 5 minutes, and in 88% (seven of eight) of dogs treated with t-PA, hirulog, and ridogrel at 37 +/- 10 minutes (comparison of the frequency of and the time to reperfusion, both p < 0.01). Among the dogs with reestablished coronary blood flow, reocclusion developed in the one treated with t-PA alone at 36 minutes after reperfusion, in seven of the seven treated with t-PA plus hirulog at 66 +/- 15 minutes, and in two of the seven treated with t-PA, hirulog, and ridogrel at 151 +/- 21 minutes (comparison of the frequency of and time to reocclusion, both p < 0.05). Reocclusion was not detected in the one dog treated with t-PA and ridogrel or in the other five dogs treated with t-PA, hirulog, and ridogrel within 180 minutes after reperfusion. Hirulog prolonged and maintained activated clotting times at a level twice that of baseline values. Hirulog inhibited ex vivo platelet aggregation induced by thrombin, and ridogrel inhibited platelet aggregation induced by U46619, a thromboxane mimetic., Conclusions: Inhibition of thrombin in addition to treatment with t-PA enhances thrombolysis. A combination of inhibition of thrombin and thromboxane synthetase and blockade of thromboxane A2 receptor enhances thrombolysis and delays or may prevent reocclusion of the recanalized coronary arteries.

The role of recurrent platelet aggregation in the development of neointimal proliferation of coronary arteries was explored in this study, and the hypothesis was evaluated that recurrent platelet aggregation and the consequent frequency and severity of cyclic coronary blood flow variations are important pathophysiologic factors in the subsequent development of neointimal proliferation. In 24 chronically instrumented dogs, variable degrees of coronary artery neointimal proliferation were observed 3 weeks after mechanical injury of the arterial endothelium and the placement of an external coronary artery constrictor. The severity of neointimal proliferation at 21 days was closely related to the frequency and severity of cyclic coronary blood flow variations during the initial 7 days after instrumentation of the animals, itself a manifestation of recurrent platelet aggregation and dislodgement. Pharmacological therapy with a dual thromboxane A2 synthetase inhibitor and receptor antagonist and with a serotonin S2 receptor antagonist frequently was successful in abolishing cyclic blood flow variations and in retarding neointimal proliferation.

Platelet-mediated obstruction of stenotic and endothelium-injured coronary arteries may be important in the abrupt progression from chronic stable to unstable coronary heart disease syndromes in patients. Transcardiac accumulation of thromboxane A2 and serotonin has been demonstrated in patients as chronic stable angina is converted to unstable angina. In this study in anesthetized open chest dogs with coronary artery stenosis and endothelial injury, thromboxane A2 and serotonin were shown to be important mediators of intermittent coronary obstruction caused by platelet aggregation and dynamic vasoconstriction. Furthermore, thromboxane A2 synthesis inhibitors and receptor antagonists and serotonin receptor antagonists, singly and together, provided substantial protection against repetitive platelet aggregation and dislodgment in canine models with coronary artery stenosis and endothelial injury even when systemic catecholamine concentrations were markedly elevated. These same observations apply in chronically instrumented, awake, unsedated dogs with coronary artery stenosis and endothelial injury in which recurrent platelet attachment and dislodgment cause cyclic flow alterations that may be prevented by thromboxane A2 synthesis inhibitors and receptor antagonists and serotonin receptor antagonists. Chronically instrumented dogs with coronary stenosis and endothelial injury in which recurrent platelet attachment and dislodgment occurred also developed neointimal proliferation of varying severity within 10 days to 3 weeks; the morphologic appearance of the neointimal proliferation was identical to that found in patients who develop restenosis after coronary angioplasty.

Background: Studies in animals have shown that serotonin constricts coronary arteries if the endothelium is damaged, but in vitro studies have revealed a vasodilating effect on isolated coronary segments with an intact endothelium. To investigate the effect of serotonin in humans, we studied coronary-artery cross-sectional area and blood flow before and after the infusion of serotonin in seven patients with angiographically normal coronary arteries and in seven with coronary artery disease., Methods: We measured the cross-sectional area of the coronary artery by quantitative angiography and coronary blood flow with an intracoronary Doppler catheter. Measurements were obtained at base line and during intracoronary infusions of serotonin (0.1, 1, and 10 micrograms per kilogram of body weight per minute, for two minutes). We repeated the measurements after an infusion of ketanserin, an antagonist of serotonin receptors that is thought to block the effect of serotonin on receptors in the arterial wall but not in the endothelium., Results: In patients with normal coronary arteries, the highest dose of serotonin increased cross-sectional area by 52 percent (P less than 0.001) and blood flow by 58 percent (P less than 0.01). The effect was significantly potentiated by administration of ketanserin. In patients with coronary-artery atherosclerosis, serotonin reduced cross-sectional area by 64 percent (P less than 0.001) and blood flow by 59 percent (P less than 0.001). Ketanserin prevented this effect., Conclusions: Serotonin has a vasodilating effect on normal human coronary arteries; when the endothelium is damaged, as in coronary artery disease, serotonin has a direct, unopposed vasoconstricting effect. When considered with other evidence, these data suggest that platelet-derived factors such as serotonin may have a role in certain acute coronary ischemic syndromes.

This study was designed to test the efficacy of nitroglycerin and diltiazem in inhibiting in vivo platelet aggregation and reducing platelet-mediated vasoconstriction in a canine model of coronary artery stenosis and endothelial injury. Coronary artery diameter was measured in vivo by means of ultrasonic crystals sutured on the left anterior descending coronary artery (LAD) immediately distal to an external constrictor (LAD1), 1 cm below (LAD2), and on the left circumflex coronary artery. Coronary diameter was continuously measured before, during cyclic flow variations (progressive declines in blood flow followed by sudden restorations of flow due to recurrent intracoronary platelet aggregation), during cyclic flow variations and intravenous infusion of nitroglycerin (5 micrograms/kg per min) or diltiazem (15 micrograms/kg per min), and after cyclic flow variations were abolished by administration of LY53857, a serotonin receptor antagonist (n = 7), or SQ29548, a thromboxane A2 receptor antagonist (n = 7). During control cyclic flow variations, at the nadir of coronary flow (6% to 11% of the nonstenosed values), LAD1 cross-sectional area decreased by 43 +/- 8% and 44 +/- 3% in the two groups of dogs subsequently treated with LY53857 and SQ29548, respectively. Neither nitroglycerin nor diltiazem caused changes in cyclic flow variation frequency or severity. Furthermore, neither drug significantly reduced the vasoconstriction associated with cyclic flow variations, whereas they significantly increased circumflex artery cross-sectional area. In contrast, LY53857 and SQ29548 were very effective in abolishing cyclic flow variations and the coronary vasoconstriction related to them. Five additional dogs received an intracoronary infusion of nitroglycerin (21 +/- 5 micrograms/kg per min) and later diltiazem (15 micrograms/kg per min).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary vascular injury promotes blood cell-vessel wall interactions that influence arachidonic acid metabolism and coronary blood flow patterns. Since lipoxygenase and cytochrome P-450 epoxygenase metabolites of arachidonic acid are synthesized by vascular and inflammatory cells and have a variety of important biological actions, we investigated the metabolism of arachidonic acid by these pathways in normal and stenosed, endothelially injured canine coronary arteries. We found and confirmed by gas chromatography/mass spectrometry that primarily 12- and 15-hydroxyeicosatetraenoic acids (HETEs) are synthesized by both coronary artery segments. Lesser amounts of 11-, 9-, 8-, and 5-HETEs are also produced. 15-Ketoeicosatetraenoic acid is also synthesized. The synthesis of 14C-HETEs is fivefold to 10-fold greater by the stenosed than the normal coronary artery. Specific radioimmunoassays indicated that the stenosed coronary artery synthesized 93 +/- 14 and 1,102 +/- 154 ng/g of tissue of 15- and 12-HETE, respectively, while the normal coronary artery produced 17 +/- 3 and 162 +/- 68 ng/g of tissue of 15- and 12-HETE, respectively. Products comigrating with 14,15-; 11,12-; 8,9-; and 5,6-epoxyeicosatrienoic acids (EETs) and the corresponding dihydroxyeicosatrienoic acids (DHETs) were detected predominantly in stenosed coronary arteries by high-pressure liquid chromatography. The structures of the EETs were confirmed by GC/MS. The EETs and prostaglandin I2 produced endothelium-independent, concentration-related relaxations of dog coronary artery rings. These data indicate that normal and stenotic coronary arteries metabolize arachidonic acid to HETEs, DHETs, and EETs along with prostaglandins; however, the synthesis of these metabolites is greater in the stenosed, endothelially injured vessel. The EETs may be synthesized during the development of cyclic flow variations and counteract the vasoconstrictor effects of thromboxane A2.

The goal of the present study was to demonstrate that intracoronary platelet deposition may trigger intense vasoconstriction of large epicardial coronary arteries in vivo and that this is largely mediated by thromboxane A2 and serotonin released by activated platelets. Cyclic flow variations (progressive declines in blood flow followed by sudden restorations of flow) due to recurrent intracoronary platelet activation and thrombus formation were induced by damaging the endothelium and placing a cylindrical constrictor on the left anterior descending coronary artery (LAD) in open-chest, anesthetized dogs. Coronary diameters were measured in vivo by means of ultrasonic crystals sutured on the LAD immediately distal to the constrictor (LAD1) and 1 cm below (LAD2) and on the circumflex coronary artery (Cx). Coronary artery diastolic diameters were measured continuously before and during cyclic flow variations and after they were abolished by administration of LY53857, a serotonin-receptor antagonist (group 1, n = 7), or SQ29548, a thromboxane-receptor antagonist (group 2, n = 7). During cyclic flow variations, at the nadir of coronary flow, LAD1 (a site of maximal platelet accumulation) cross-sectional area decreased by 52 +/- 10% and 38 +/- 6% in group 1 and 2 animals, respectively (p less than 0.001 compared with values recorded during a brief LAD occlusion obtained by a suture snare), whereas LAD2 (a site of minimal or no platelet accumulation) cross-sectional area did not differ from that recorded during the brief LAD occlusion. SQ29548 abolished cyclic flow variations in seven of seven dogs and LY53857 in six of seven, but they affected the increased coronary vasoconstriction differently: LAD1 cross-sectional area increased by 32 +/- 6% of the control value in SQ29548-treated animals, whereas it returned to baseline dimension values in the LY53857-treated group as these interventions also abolished the cyclic flow variations. We conclude that a marked coronary vasoconstriction may be triggered by local platelet deposition and that thromboxane A2 and serotonin are mediators of this vasoconstriction.

We have reported previously that thromboxane A2 (TXA2) and serotonin (5-HT, 5-hydroxytryptamine) are important mediators of cyclic flow variations (CFVs) in a canine model of coronary artery stenosis and endothelial injury. The present study tested the hypothesis that a TXA2 receptor antagonist is more effective in reducing intracoronary platelet deposition at sites of endothelial injury and severe stenosis than a 5-HT2 receptor antagonist. CFVs developed after placing a plastic constrictor around the left anterior descending coronary artery (LAD) in 51 of 56 dogs. Autologous platelets labeled with 111In were injected in 48 animals. Ten control dogs (group 1A) were killed after CFVs were observed for 1 hour at the nadir of coronary blood flow. Five dogs (group 1B) did not develop CFVs after placement of the constrictor. CFVs were abolished with SQ 28668 (2.75 +/- 0.36 mg/kg, group 2) and SQ 29548 (0.45 +/- 0.1 mg/kg, group 3), two different TXA2 and PGH2 receptor antagonists, in eight of 10 and six of seven dogs, respectively. In eight of 10 dogs (group 4), CFVs were abolished with ketanserin (0.66 +/- 0.12 mg/kg), a 5-HT2 receptor antagonist. In group 2, 3, and 4 dogs, the respective drugs were given so that the minimal dose required to abolished CFVs was administered. In six of six dogs (group 5), a higher dose of ketanserin (i.e., 1.5 mg/kg) was used to abolish CFVs. At death, intracoronary platelet deposition was evaluated by calculating the LAD platelet accumulation ratio (111In activity in the LAD/111In activity in the circumflex coronary artery) in 43 dogs and, in 22 dogs, by microscopic examination of the LAD. A marked LAD platelet accumulation ratio was found in group 1A dogs at the stenotic site and in segments immediately distal to it. The LAD platelet accumulation ratio was significantly reduced by both the low and the high doses of ketanserin compared with group 1A dogs (p less than 0.001). However, the two TXA2 receptor antagonists further reduced the LAD platelet accumulation ratio compared with ketanserin-treated animals (p less than 0.01). Microscopic examination confirmed these findings. We conclude that SQ 28668 and SQ 29548, two different TXA2 receptor antagonists, reduce residual intracoronary platelet deposition associated with CFVs in this canine model more effectively than ketanserin, a 5-HT2 receptor antagonist.

This light microscopic autoradiographic study was performed to test the hypotheses that (a) the density of beta adrenergic receptors (BAR) may differ in various components of the heart and (b) BAR in certain components of the heart may exhibit a selective response to pharmacologic and pathological stimuli. Blocks of canine left ventricle were frozen and tissue sections cut and incubated in (-)[3H]dihydroalprenolol (DHA) to label the BAR. For total and nonspecific binding, serial sections were incubated with and without 10(-5) M (+/-)propranolol. Scintillation spectrometry of sections demonstrated rapid binding, saturability, stereospecificity, a dissociation constant (KD) of 3.2 +/- 0.5 nM (SD) (n = 3), and a maximal binding of 31.3 +/- 3.1 fmol/mg of tissue protein. Isoproterenol was 12.5 times more effective than norepinephrine in displacing DHA. Sections incubated with 10(-5) - 10(-8) M metoprolol, a beta one selective antagonist, demonstrated a KD of 0.7 X 10(-6) M. For autoradiography, emulsion-coated coverslips were attached to the slides. After exposure, the slides were developed and stained, and grain density quantified. Specific BAR binding (n = 4 dogs) was 1,047 +/- 131 (SEM) grains/10(-2) mm2 for myocardial arterioles, 219 +/- 30 for myocardial arteries, 31 +/- 12 for the proximal left anterior descending coronary artery (LAD), and 231 +/- 34 for cardiac myocytes. Specific binding in the presence of 10(-5) M metoprolol was reduced approximately 75% for both arterioles and myocytes. However, at 10(-6) M metoprolol, the percent reduction in specific DHA binding was greater for myocytes (50%) than for arterioles (0%), and at 10(-7) M metoprolol, the percent reduction in specific DHA binding was 17% for myocytes with no reduction over arterioles. After 1 h of LAD occlusion, a selective increase (18%) in BAR density occurred over cardiac myocytes, but not over blood vessels in the ischemic myocardium. Thus, (a) specific BAR binding was five times greater in arterioles than in small arteries and myocardium and 34 times greater than in the proximal LAD; (b) BAR of myocytes were more sensitive than those of arterioles to displacement by the beta one selective antagonist, metoprolol; and (c) a selective increase in BAR occurs in cardiac myocytes but not in blood vessels after 1 h of ischemia in this experimental model.

The effect of hypertonic mannitol on pressor responses to vasoactive agents was studied in isolated canine coronary arteries perfused with physiologic salt solution at a constant flow. When perfusion pressure was increased with 60 mM KCl, mannitol (50 mosM) consistently caused a decrease in perfusion pressure that lasted for at least 1 h. Withdrawal of mannitol from the perfusion media was associated with a vasoconstrictor response that was not prevented by alpha- or beta-adrenoceptor blockade or by the presence of either nitroglycerin or norepinephrine. Hypertonic mannitol also reduced the responsiveness of the isolated smooth muscle preparations to several different mechanistically unrelated vasodilator agents. The mechanism(s) responsible for the paradoxical ability of hypertonic mannitol to reduce vascular responsiveness to both vasoconstrictor and vasodilator interventions in isolated canine coronary arteries is not known, but future studies should be directed at elucidating it as well as determining whether similar phenomena occur in vivo.

Thromboxane A2 exerts powerful effects on vascular smooth muscle tone and platelet aggregability. Previous studies have demonstrated increases in transcardiac thromboxane B2 (a stable thromboxane A2 metabolite) in patients with unstable angina and recent chest pain. To determine whether these increases in transcardiac thromboxane B2 are unique to the unstable anginal syndrome or are merely a consequence of ongoing myocardial ischemia, simultaneous ascending aortic and coronary sinus blood samples were obtained for quantitation of thromboxane B2 in 52 patients with a history of chest pain. Provocation was performed with (1) rapid cardiac pacing in 23 patients, (2) cold pressor stress in 19 patients, and (3) sustained isometric exertion in 10 patients. Of the 52 patients, only 5 had a substantial (greater than 3-fold) increase in coronary sinus thromboxane B2 in response to provocation: 1 had unstable angina and chest pain during the previous 48 hours and 4 had a myocardial infarction within the previous 6 weeks. Similarly, only 7 had a greater than 3-fold increase in the coronary sinus/aortic thromboxane B2 ratio in response to provocation: 1 had unstable angina and recent chest pain, 5 had a recent myocardial infarction, and 1 had both of these. There were no other clinical features unique to these patients. The remaining patients with similar diagnoses did not develop a marked increase in coronary sinus thromboxane B2 or the coronary sinus/aortic thromboxane B2 ratio with provocation. None of the 35 patients with stable ischemic heart disease or nonischemic chest pain syndromes had a substantial increase in coronary sinus thromboxane B2 or the coronary sinus/aortic thromboxane B2 ratio (p less than 0.001 for both coronary sinus thromboxane B2 and the coronary sinus/aortic thromboxane B2 ratio in comparison with the 17 patients with recent unstable angina or myocardial infarction). Thus, generous amounts of thromboxane B2 are released into the coronary circulation after provocation in some patients with unstable angina or recent myocardial infarction but not in those with stable ischemic heart disease or nonischemic chest pain syndromes.

Whereas numerous studies have investigated the role of prostacyclin and thromboxane A2 in the maintenance of coronary blood flow, most of these have focused on normal vessels. In the present investigation, we examined the prostaglandin- and thromboxane-synthesizing capacity of isolated coronary artery segments obtained from the site of a critical coronary artery stenosis. Cyclic flow variations were produced by placing a hard cylindrical constrictor on the proximal left anterior descending coronary artery in open-chest, anesthetized dogs. Cyclic flow variations are characterized by progressive declines in coronary blood flow, interrupted by sudden spontaneous restorations of flow. After cyclic flow variations had been induced, the hearts were removed, and the left anterior descending and circumflex coronary arteries were dissected. The vessels were cut into segments and incubated in the presence of increasing concentrations of arachidonic acid (10(-4)-10(-6) M). The synthesis of prostaglandin E2, thromboxane B2, and 6-keto prostaglandin F1 alpha by the coronary segments was measured by radioimmunoassay. When incubated in the presence of 10(-5) M arachidonic acid, coronary artery segments obtained from the left anterior descending coronary artery undergoing cyclic flow variations produced substantially more thromboxane B2 (142 +/- 27 vs. 29 +/- 3 pg/mg P less than 0.01) and less 6-keto prostaglandin F1alpha (125 +/- 12 vs. 350 +/- 30 pg/mg, P less than 0.01) than control circumflex coronary artery segments. Circumflex coronary vessels in which the endothelium was removed ex vivo produced 6-keto prostaglandin F1alpha levels comparable to those found in the left anterior descending coronary artery (147 +/- 17 pg/mg), but did not synthesize thromboxane B2 (23 +/- 2.6 pg/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Heparin has been labeled with [99mTc] pertechnetate and its ability to image damaged coronary vessels and myocardium during and following myocardial ischemia has been studied in experimental animals. The data obtained indicate that Tc-99m heparin localizes in damaged myocardium and coronary vessels in canine models of temporary myocardial ischemia and reperfusion and in damaged myocardium during fixed coronary occlusion. Scintigraphic detection of damaged myocardium was possible in both models, but the highest levels of Tc-99m heparin in damaged myocardial tissue were found in those dogs with temporary coronary occlusion and reflow. The data suggest that Tc-99m heparin may be of value as a positive imaging agent when coronary arteries or myocardium are injured and either reperfusion is allowed and/or significant blood flow persists in the damaged area.

Cyclic variations in coronary blood flow (CFVs) in dogs with experimental coronary artery stenosis and endothelial injury appear to result primarily from the aggregation of platelets at the site of stenosis followed by dislodgement and distal embolization. Using this canine model, we tested the hypotheses: (a) that thrombin is an important mediator of CFVs in dogs with coronary stenoses and endothelial injury; (b) that inhibition of thrombin with heparin, or MCI-9038, a selective thrombin inhibitor, abolishes CFVs in this model; and (c) that abolition of CFVs by thrombin inhibition is time dependent. CFVs, produced in open-chest dogs by placing a flow-reducing plastic constrictor around the left anterior coronary artery, were monitored for either 30 min (group I) or 3 h (group II) before treatment with either heparin or 4-methyl-1-(N2-[(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl (MCI-9038). In group I, cyclic flow variations were abolished by heparin in 12 of 18 dogs and by MCI-9038 in 5 of 7 dogs. In group II, cyclic flow variations were not abolished by heparin in any of seven dogs and were abolished by MCI-9038 in only one of seven dogs. Thus, (a) thrombin appears to be an important mediator of cyclic flow variations in dogs with coronary artery stenosis and endothelial injury and (b) inhibition of thrombin abolishes CFVs after short but not prolonged periods of CFVs.

To determine the safety and benefit of n-3 fatty acid therapy in the prevention of early restenosis after coronary angioplasty, we conducted a randomized, unblinded study comparing a conventional antiplatelet regimen (325 mg of aspirin and 225 mg of dipyridamole per day; control group) with a similar regimen supplemented with 3.2 g of eicosapentaenoic acid per day (treatment group). Treatment began seven days before angioplasty and continued for six months afterward. All angiographic analyses were blinded and performed by a method that was validated by comparison with quantitative coronary angiography. In 82 male patients, 103 coronary lesions were dilated. Both groups had similar base-line clinical and angiographic characteristics. The incidence of early vessel restenosis, as determined on a second angiogram three to four months after angioplasty, was 36 percent in the control group and 16 percent in the treatment group (P = 0.026). The incidence of restenosis per patient was also significantly lower in the treatment group (46 vs. 19 percent). Both multiple logistic regression and Mantel-Haenszel statistical analyses demonstrated a significant independent benefit of treatment with n-3 fatty acids. No important bleeding complications developed in the treated patients. These results, in a male population at relatively high risk for restenosis, suggest that a dietary supplement of n-3 fatty acids, administered for one week before and for six months after coronary angioplasty, is safe and reduces the occurrence of early restenosis after that procedure. Whether this beneficial effect also applies to other populations is unknown.

The coronary vasoconstrictor properties of digitals were evaluated in 61 anesthetized, openchest dogs after coronary sinus cannulation and under conditions of a constant heart rate (atrioventricular pacing) and near-constant blood pressure. The contribution of alpha adrenergic receptor stimulation to the digitalis-induced increase in coronary vascular resistance (CVR) was examined. With Na pentobarbital anesthesia (16 dogs), intravenous acetylstrophanthidin (0.5 mg) caused a significant (P<0.05) rise in CVR from 1 through 9 min after injection. The peak increase was +11+/-2% SE of the control of 1.8+/-0.2 mm Hg/cm(3)/min. The mean time to peak effect was 3 min, and to recovery was 21 min. Prior alpha adrenergic receptor blockade with phenoxybenzamine in 11 animals reduced (P<0.05) the acetylstrophanthidin-induced peak of CVR and substantially decreased (P<0.05) the time to recovery (5 min). Intravenous digoxin (1.0 mg) with Na pentobarbital anesthesia (five dogs) had no significant effect on CVR. However, with chloralose and urethane anesthesia (nine dogs) the same dose of digoxin produced a significant rise in CVR from 3 through 30 min. The peak increase was +20+/-3% of control (1.4+/-0.1 mm Hg/cm(3)/min). One-third the dose of intravenous digoxin (0.35 mg) produced a 9.5+/-1.0% increase in CVR (five additional dogs). Myocardial oxygen consumption did not change significantly in nine dogs after intravenous digoxin. In 10 additional dogs pretreated with phenoxy-benzamine and in 7 dogs pretreated with mecamylamine, the increase in CVR did not occur after 1.0 mg of intravenous digoxin. Thus there is a coronary vasoconstrictor effect of intravenous acetylstrophanthidin and digoxin, of rapid onset, which is mediated through alpha adrenergic receptor stimulation.