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The coronary artery often reoccludes soon after the flow has been restored with recombinant tissue-type plasminogen activator (TPA) in dogs with electrically-induced thrombosis. The coronary artery reocclusion relates to intense in situ platelet activation and thrombin generation in the reperfused coronary artery. To determine the effect of a potent platelet inhibitor, the prostacyclin analog iloprost, in the prevention of coronary artery reocclusion, an occlusive thrombus was created in the left anterior descending coronary artery in 23 dogs. Coronary artery reflow occurred in 17 dogs after TPA (1 mg/kg over 20 minutes intravenously) administration. After the reflow was established, 10 dogs were given saline and 7 dogs were given iloprost (4 micrograms/kg over 40 minutes). In the saline-treated group, the coronary artery reoccluded in 8 of 10 dogs over 90 minutes (reocclusion rate 80%). In the iloprost-treated group, the coronary artery reoccluded in five of seven dogs (reocclusion rate 71%; p = NS vs TPA alone). The magnitude of peak coronary blood flow and duration of flow were similar in dogs given saline or iloprost after TPA-induced thrombolysis. Scanning electron microscopy showed residual thrombus and the appearance of coronary arterial narrowing distal to the thrombus in all dogs examined. Thus residual thrombus formation and coronary artery narrowing continue to occur after TPA-induced thrombolysis in dogs whether the animals are treated with saline or iloprost. Administration of iloprost after reflow does not modulate the frequency of coronary artery reocclusion.

Total coronary artery occlusion followed by reperfusion leads to neutrophil accumulation in the reperfused myocardium and a reduction in endothelium-dependent coronary artery relaxation. Attenuated coronary artery relaxation in the affected regions is thought to be related to breakdown of endothelium-derived relaxing factor (EDRF) by free oxygen radicals released during reperfusion. To determine if temporary subtotal coronary artery narrowing leads to similar alteration in vascular reactivity, eight open-chest dogs were subjected to 1 h of left anterior descending (LAD) coronary artery narrowing (70% reduction in basal flow) and pacing-induced increase in heart rate (30% above baseline) followed by reperfusion for 1 h. Thereafter reactivity of ischemic-reperfused LAD and nonischemic circumflex (Cx) coronary artery rings to the thromboxane A2 analog U46,619 and EDRF-dependent vasorelaxants acetylcholine (ACh), thrombin, and adenosine diphosphate (ADP), as well as to EDRF-independent vasorelaxant nitroglycerin (NTG), was examined. Unlike in the setting of total coronary artery occlusion, reperfused myocardium or LAD did not reveal neutrophil infiltration. However, contraction in response to U46,619 was markedly (P < .001) increased in the LAD rings compared to that in the Cx rings. ACh-induced relaxation was only modestly decreased (P < .05) in the LAD coronary artery rings, but the relaxation in response to both thrombin and ADP was markedly diminished (P < .01) as compared to that in the Cx rings. Coronary artery ring relaxation in response to NTG was preserved in the LAD rings. Pretreatment of coronary artery rings with indomethacin did not alter the enhanced contraction or diminished endothelium-dependent relaxation of LAD coronary artery rings.(ABSTRACT TRUNCATED AT 250 WORDS)

The coronary artery produces large amounts of prostacyclin (PGI2) and a small amount of thromboxane A2 (TXA2); this high PGI2/TXA2 ratio contributes to the antithrombotic properties of the coronary artery. This study was designed to determine whether this ratio changes after coronary artery thrombosis and thrombolysis and accounts for coronary artery reocclusion. Anesthetized dogs (N = 12) were subjected to electrically induced coronary artery thrombosis and tissue plasminogen activator-induced thrombolysis. Thrombolysis was achieved in 11 dogs, and the coronary artery reoccluded in five of these dogs after the initial reperfusion. Spontaneous and ionophore A23,187-stimulated PGI2 and TXA2 synthesis in normal circumflex and ischemic-reperfused left anterior descending coronary artery segments was measured by radioimmunoassay of thromboxane B2 and 6-keto-prostaglandin F1 alpha, respectively. Production of TXA2 was 413% to 656% greater in left anterior descending segments (from the region of thrombosis and sites proximal and distal to the thrombus) compared with normal circumflex segments (p < 0.001). Production of PGI2 was also increased but only by 46% to 80% in the left anterior descending segments compared with normal circumflex segments (p < 0.05). TXA2 production was greater in coronary artery segments that reocculded compared with segments that stayed open (p < 0.02). Scanning electron microscopy revealed platelet deposition in thrombosed left anterior descending segments but not in segments proximal or distal to the thrombus site, indicating that the vascular wall per se may be a source of increased production of TXA2.(ABSTRACT TRUNCATED AT 250 WORDS)

A three-arm prospective randomized trial was designed to compare the effectiveness of single drug therapy with imipenemcilastatin (IC), two-drug therapy with ceftazidime-vancomycin (CV), and three-drug therapy with ticarcillin-vancomycin-amikacin (TVA) for the empirical antimicrobial treatment of febrile neutropenia events. The objectives of the study were to determine whether IC monotherapy was as effective as combination drug therapy (CV or TVA) and to assess the value of adding vancomycin at initiation of treatment. One hundred eighty-three febrile neutropenia events were randomized and 125 were evaluable. Success rates were 73% with IC, 67% with CV, and 72% with TVA. There were no statistically significant differences between the three treatment groups, regardless of the duration and severity of neutropenia. Fifty-four bacterial isolates were recovered from 43 patients. Among recovered bacterial strains, 55% were Gram-negative and 45% were Gram-positive. Rates of bacteriologically documented failures (14/33) and superinfections (3/33) were similar in the three groups. Adverse events were rare but two patients given CV and three given TVA developed severe skin toxicity requiring modification of the antimicrobial regimen. IC alone showed similar effectiveness and less toxicity, as compared with CV or TVA. Vancomycin given initially increased toxicity but failed to improve the success rate. Vancomycin may be appropriate only in patients at high risk for infection with methicillin-resistant staphylococci.

Numerous attempts have been made to prevent restenosis after successful transluminal dilation of an atherosclerotic vessel using a variety of pharmacologic and mechanical approaches. This article reviews the pathobiology of the restenosis process, offers a hypothesis as to its cause, reviews attempts to modify the process, and outlines therapeutic approaches to future treatment.

Aim: To study the determinants (or mechanisms) of isolated systolic hypertension in the elderly., Methods: Pulsatile blood pressure and flow (multisensor catheter) were measured in the ascending aorta and impedance spectra were calculated in 18 subjects undergoing cardiac catheterization. Nine subjects (mean +/- SEM age 58 +/- 1.4 years) had increased aortic systolic (166 +/- 2.3 mmHg, P < 0.001), mean (116 +/- 2.1 mmHg, P < 0.02) and pulse blood pressure (83 +/- 2.1 mmHg, P < 0.001) and normal diastolic blood pressure (84 +/- 2.0 mmHg, NS) and constituted the isolated systolic hypertension group. The other nine age-matched (58 +/- 1.1 years) subjects had normal aortic systolic and diastolic blood pressure and constituted the normotensive control group., Results: Both static (peripheral vascular resistance) and dynamic (characteristic impedance and wave reflection) components of left ventricular external load (aortic input impedance) were elevated in the isolated systolic hypertensives compared to the normotensive subjects; peripheral vascular resistance was 44% higher (P < 0.001), characteristic impedance (index of aortic stiffness) was 107% higher (P < 0.001), the first harmonic of impedance moduli (index of wave reflection) was 57% higher (P < 0.004) and the first impedance moduli minimum was shifted to a higher frequency (from 3.4 +/- 0.2 Hz to 4.2 +/- 0.13 Hz, P < 0.008) in the group with isolated systolic hypertension., Conclusions: The changes in impedance spectra in the isolated systolic hypertensives indicate that the cross-sectional area of the peripheral vascular bed was reduced and that the aorta and large arteries were stiffer, producing an increased pulse wave velocity and an early return of pulse wave reflection in systole. The marked increase in arterial stiffness in isolated systolic hypertension offset the increase in diastolic blood pressure that would have been expected from an increase in peripheral vascular resistance alone, and early return of the reflected pressure wave augmented aortic pressure throughout systole and accounted for the large increase observed in systolic and pulse pressure in the aorta.

Objective: Previous studies have shown variable effects of human and canine polymorphonuclear leucocytes (neutrophils) on vascular tone. The aim of this study was to identify whether these variations in neutrophil function are due to species differences., Methods: Canine and human arterial rings (with and without endothelium) were contracted with the thromboxane A2 analogue U46619, and then exposed to isolated neutrophils., Results: Human neutrophils caused a significant relaxation of the human mammary arterial rings, and the relaxation was unaffected by the cyclo-oxygenase inhibitor indomethacin, enhanced by superoxide dismutase (SOD), and inhibited by oxyhaemoglobin. The relaxant effect of human neutrophils was also diminished upon pretreatment with NG-monomethyl-l-arginine (L-NMMA), indicating that the vasorelaxant material released by the neutrophils was nitric oxide (NO). Human neutrophils also relaxed canine femoral arterial rings, and the relaxant effect was potentiated by SOD and inhibited by pretreatment with oxyhaemoglobin or L-NMMA, confirming that the vasorelaxation was via release of NO. Canine neutrophils, on the other hand, caused an endothelium dependent contraction of autologous femoral arterial rings. This vasoconstriction was not affected by indomethacin, SOD, oxyhaemoglobin, or L-NMMA. However, treatment of canine neutrophils with the 5-lipoxygenase inhibitor piriprost attenuated (p < 0.02) their contractile effect on vascular rings, suggesting that neutrophil generated 5-lipoxygenase products were probably responsible for smooth muscle contraction. Presence of the leukotriene C4 and D4 receptor antagonist FPL 55,712 totally blocked the contractile effects of canine neutrophils, indicating that femoral arterial ring contraction was mediated by peptido-leukotrienes., Conclusions: The endothelium dependent nature of the canine neutrophil induced contraction suggests that the 5-lipoxygenase product leukotriene A4 is taken up by endothelial cells for conversion to peptido-leukotrienes. Since SOD had no effect and FPL 55,712 totally blocked the vasoconstrictor effects of canine neutrophils, it appears that the vasoconstrictor effects of the latter are mediated primarily through peptido-leukotrienes. In contrast, the vasorelaxation by human neutrophils is mediated through release of NO.

Rethrombosis of the infarct-related artery after pharmacologic thrombolysis is a major limitation of the thrombolytic therapy. Platelet and fibrin deposition in the coronary artery after recombinant tissue-type plasminogen activator (rTPA) may play a leading role in reformation of thrombus. Therefore we examined the effect of low molecular weight heparin (LMWH) as adjunctive treatment with rTPA in a dog model of electrically induced intracoronary thrombus. Fourteen dogs, in which a stable coronary thrombus was induced with delivery of 100 microA of anodal direct current, were randomly given an intravenous bolus of LMWH, 75 IU/kg (n = 6), or saline (n = 8), followed by intravenous rTPA, 1 mg/kg over 20 minutes. LMWH (75 IU/kg) or saline was continuously infused over 90 minutes after rTPA-induced thrombolysis. Reperfusion occurred at 29 +/- 7 minutes in six of eight dogs receiving rTPA plus saline (reperfusion rate 75%), while reperfusion occurred at 18 +/- 3 minutes in all six dogs receiving rTPA plus LMWH (both p = NS versus rTPA plus saline group). Coronary reocclusion occurred in 83% of dogs given rTPA plus saline, but only in one dog (17%) given rTPA plus LMWH (p less than 0.05). Magnitude of reflow at 60 minutes of reperfusion was higher in the rTPA plus LMWH group than in the rTPA plus saline group (51 +/- 14 ml/min versus 10 +/- 9 ml/min; p less than 0.05). As expected, partial thromboplastin time was greater in rTPA plus LMWH than in rTPA plus saline-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary artery reocclusion after thrombolysis with human recombinant tissue-type plasminogen activator (rt-PA) is related to the short half-life of this agent in plasma. K2P, a mutant of rt-PA lacking the fibronectin fingerlike, epidermal growth factor-like and first kringle domains (amino acids 6 to 173) and having the glycosylation site Asn184 mutagenized to Gln, has been produced in Chinese hamster ovary cells. In this study we compared the thrombolytic effect of K2P and rt-PA in dogs with electrically induced coronary artery thrombosis. Both agents were given intravenously in equimolar amounts over 20 min after the occlusive thrombus was stable for 30 min; dogs were monitored for 1 h after reperfusion if flow occurred. Coronary blood flow was restored by rt-PA in 6 (60%) of 10 dogs. The restored flow lasted for 49 +/- 12 min and mean flow at 60 min from the start of reperfusion was 7 +/- 3 ml/min. The reocclusion rate was 50% (three of six dogs). Flow was restored in five (100%) of five dogs by K2P. The restored blood flow lasted during the entire 1-h observation period in all but one dog and mean flow at 60 min was 49 +/- 16 ml/min (p less than 0.02 vs. flow in rt-PA-treated dogs). Restored coronary blood flow showed marked cyclic flow variations in rt-PA-treated but not in K2P-treated dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

It is generally recognized that formation of a platelet-fibrin-rich thrombus in an atherosclerotic coronary artery is the basis of unstable angina and acute myocardial infarction. Platelet hyperactivity has been identified in coronary risk factors such as hyperlipidemia and diabetes mellitus. Persistent activation of these cells results in release of growth factors that may contribute to the progression of atherosclerosis. Several recent studies show that endothelium, by generating or metabolizing a host of vasoactive substances, plays a critical role in the modulation of vascular tone. Important among these substances are prostacyclin (PGI2) and endothelium-derived relaxing factor (EDRF). The endothelium-dependent modulation of coronary artery tone correlates with the severity of atherosclerosis and the number of coronary risk factors. Procedures such as angioplasty and coronary bypass surgery injure the endothelium. The loss of endothelial smooth muscle relaxant function may contribute to the vasoconstriction and thrombosis often observed soon after these procedures. Thrombolysis (and subsequent reperfusion of the coronary artery) is also associated with severe endothelial dysfunction, with a resulting vasoconstrictor influence on the coronary vascular bed. Activation of leukocytes and their presence in the reperfused myocardium contribute to progression of myocardial injury by release of oxygen free radicals and proteolytic enzymes. Thus, it seems that a perturbation in this delicate equilibrium in cellular interactions relates to genesis and progression of myocardial ischemia.

Leukocyte-derived elastase is released following coronary artery occlusion and reperfusion and may contribute to reperfusion-related myocardial injury. Leukocyte infiltration into the reperfused myocardium may also contribute to ischemic injury following reflow. In the present study, we examined the effects of tissue-plasminogen activator (t-PA, 1 mg/kg over 20 minutes) given intravenously with either saline or a leukocyte elastase inhibitor (ICI 200,880, 5 mg/kg) in dogs with electrically-induced coronary artery thrombosis. ICI 200,880 administration increased elastase inhibitory activity without affecting t-PA and plasminogen activator inhibitor (PAI-1) activities. Time to reflow, magnitude of peak coronary blood flow, and duration of reflow were not different in dogs given t-PA with saline or with the elastase inhibitor. However, administration of the elastase inhibitor decreased the histologically-determined leukocyte infiltration and severity of myocardial injury in dogs subjected to coronary artery thrombosis and subsequent thrombolysis. These early observations suggest that elastase release during reperfusion may be an important mediator of anoxia-reoxygenation-mediated tissue injury.

Thrombolytic effects of tissue-type plasminogen activator (t-PA) are limited by in vivo platelet activation and dynamic coronary vasoconstriction. To examine if the concurrent administration of a fibrin(ogen)-degradation product, pentapeptide 6A (Ala-Arg-Pro-Ala-Lys) with t-PA would improve the thrombolytic effects of t-PA, dogs with electrically induced coronary thrombus were given t-PA alone or with peptide 6A. In dogs given t-PA alone (0.75 mg/kg over 20 min), coronary blood flow was restored in 69% of animals (9 of 13 dogs), with a mean time to reflow of 21 +/- 10 min and duration of reflow of 35 +/- 18 min. Reocclusion occurred in 77% of dogs (7 of 9 dogs). With concurrent administration of peptide 6A (200 mumol), coronary venous 6-keto-PGF1 alpha concentrations increased from 221 +/- 71 to 422 +/- 161 pg/ml (p less than 0.05), but not with t-PA given alone. Coronary blood flow was restored in 7 of 11 dogs (reperfusion rate 64%), with mean time to reflow of 17 +/- 7 min and duration of reflow of 35 +/- 15 min. The coronary reocclusion rate was 86%. All these indices of thrombolysis were similar to those in dogs given t-PA alone. In ex vivo experiments, we also demonstrated release of endothelium-derived relaxing factor from canine coronary artery rings in response to peptide 6A. To further examine the role of prostacyclin (PGI2) in thrombolytic response to t-PA, eight other dogs were given t-PA with a PGI2 analog iloprost (100 ng/kg/min for 40 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Unstimulated polymorphonuclear leukocytes (PMNLs) release nitric oxide or a like material that relaxes vascular tissues. To determine the effects of activated PMNLs on vascular tone, precontracted rat aortic rings were exposed to ionophore A23187-treated PMNLs. Whereas "unstimulated" PMNLs caused 29 +/- 4% relaxation, "stimulated" PMNLs caused initial contraction followed by 90 +/- 7% relaxation of aortic rings. Indomethacin or the 5-lipoxygenase blocker piriprost had no effect on PMNL-induced initial contraction or subsequent relaxation. However, initial contraction was abolished and the subsequent vasorelaxation attenuated (22 +/- 5%) by the superoxide radical scavenger superoxide dismutase (SOD), suggesting that release of superoxide radicals may have induced vascular contraction and caused endothelial damage that would permit unopposed vasorelaxant effect of PMNLs. To examine this hypothesis, aortic rings were exposed to superoxide radicals (generated by xanthine plus xanthine oxidase, X + XO) or manually deendothelialized. These rings revealed marked relaxation (78 +/- 6 and 85 +/- 6%, respectively) in response to unstimulated PMNLs. These observations suggest that stimulated PMNLs exert an initial vasoconstrictor effect and a subsequent vasorelaxant effect in response to release of superoxide radicals and nitric oxide, respectively. Arachidonate metabolites or 5-lipoxygenase products do not appear to be important in the actions of PMNLs on vascular smooth muscle.

Study Objective: The aim was to examine the effect of glyceryl trinitrate, a potent coronary vasodilator, on the thrombolytic effects of tissue type plasminogen inhibitor (t-PA) in dogs with coronary thrombosis., Design: The thrombus was formed by delivery of anodal direct current into the left anterior descending coronary artery. Fourteen dogs were randomly given t-PA alone (0.75 mg.kg-1 over 20 min) or t-PA with glyceryl trinitrate (125 micrograms.min-1 for 40 min). In four other dogs, glyceryl trinitrate was given after t-PA induced thrombolysis. Its effect on t-PA induced thrombolysis, in terms of reperfusion rate, time to thrombolysis, peak coronary blood flow, and reocclusion rate, was quantitated. Peripheral blood platelet counts and whole blood platelet aggregation were measured in all dogs. The thrombosed left anterior descending artery and normal circumflex coronary artery segments were examined by scanning electron microscopy at the end of the experiment., Measurements and Main Results: The reperfusion rate in the t-PA plus glyceryl trinitrate (t-PA + GTN) group was 57% (4/7 dogs) and with t-PA alone, 71% (5/7 dogs). The time to thrombolysis in the t-PA + GTN group was greater than with t-PA alone, at 30(SD 10) v 18(7) min, p less than 0.02, and the duration of reperfusion much shorter, at 11(17) v 48(15) min, p less than 0.02. Peak coronary blood flow in the t-PA + GTN group following reperfusion was less compared with t-PA alone, at 36(52) v 53(18) ml.min-1, p less than 0.02. Reocclusion rates in the two groups were similar. Peripheral blood platelet counts decreased during thrombus formation in all dogs; this decrease stabilised when t-PA was given alone but not when it was given with glyceryl trinitrate [mean platelet count at the end of t-PA infusion 7.23(1.68) and 4.78(3.00) X 10(8).ml-1 respectively, p less than 0.02], suggesting continued sequestration of platelets in the intracoronary thrombus in the latter group. Whole blood platelet aggregation decreased significantly with t-PA alone, but less so with t-PA + GTN [magnitude of platelet aggregation 0.23(0.57) and 5.67(6.23) ohms, respectively, p less than 0.02], suggesting lower plasma concentrations of t-PA when given with glyceryl trinitrate. Glyceryl trinitrate given after thrombolysis induced by t-PA failed to sustain reperfusion. Scanning electron microscopy of occluded left anterior descending artery showed extensive endothelial injury and a thrombus composed of platelet--red blood cells--fibrin mesh. The reperfused left anterior descending artery showed extensive endothelial injury and residual thrombus consisting mostly of fibrin and red blood cells with some platelets., Conclusion: Glyceryl trinitrate given concurrently with t-PA or after t-PA induced thrombolysis does not modify the thrombolytic potential of t-PA. The potentially "detrimental" effects of glyceryl trinitrate may be due to increase in hepatic blood flow and subsequent enhanced catabolism of t-PA. Lack of any significant effect of therapeutic dosage of glyceryl trinitrate on platelet--fibrin rich thrombus may explain the absence of a salutary action of this agent. Dynamic coronary vasoconstriction does not play an important role in coronary reocclusion after initial thrombolysis.

Dynamic coronary vasoconstriction may play a role in coronary artery reocclusion after successful thrombolysis. The effect of nitroglycerin on the thrombolytic effects of recombinant tissue-type plasminogen activator (rt-PA) was examined in dogs with an electrically induced occlusive coronary artery thrombus. Eleven dogs were randomly given rt-PA alone and seven rt-PA with nitroglycerin. The dose of rt-PA was 0.75 mg/kg body weight given over 20 min and the dose of nitroglycerin was 125 micrograms/min for 40 min. The reperfusion rate in the dogs given rt-PA alone was 73% (8 of 11 dogs) and that in the rt-PA plus nitroglycerin group was 57% (four of seven dogs) (p = NS). The time to thrombolysis (or reperfusion) in dogs receiving rt-PA plus nitroglycerin was 70% greater than in those receiving rt-PA alone (means +/- SD/29.8 +/- 9.9 versus 17.6 +/- 5.9 min, p less than 0.02), and the duration of reperfusion much shorter (11 +/- 17 versus 42 +/- 16 min, p less than 0.02). Peak coronary blood flow after reperfusion in dogs receiving rt-PA plus nitroglycerin was also less than in those receiving rt-PA alone (36 +/- 52 versus 63 +/- 20 ml/min, p less than 0.02). Reocclusion occurred in all dogs given rt-PA with nitroglycerin and in six of eight given rt-PA alone (p = NS). Plasma concentrations of rt-PA were lower when nitroglycerin was given with rt-PA alone (427 +/- 279 versus 1,471 +/- 600 ng/ml, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

The amino acid L-arginine is a precursor of endothelium derived relaxing factor (EDRF). The pentapeptide 6A (Ala-Arg-Pro-Ala-Lys) released by plasmin degradation of fibrinogen also contains arginine and relaxes vascular smooth muscle by releasing EDRF (nitric oxide). To determine and compare the effects of L-arginine, peptide 6A and a combination of L-arginine and peptide 6A on femoral artery blood flow and vascular resistance, anesthetized mongrel dog were administered saline, L-arginine, D-arginine, peptide 6A and L-arginine + peptide 6A in a random order. L-arginine and peptide 6A both induced an immediate dose-dependent short-lasting increase in femoral blood flow and a decrease in vascular resistance. Peptide 6A exerted a much greater (P less than 0.01) vasodilatory effect than did L-arginine at the same molar concentration suggesting that properties besides the arginine content are important in the effect of the pentapeptide. D-arginine had much less effect than L-arginine, indicating that the effect of L-arginine may be related to its utilization for synthesis of EDRF. When the peptide 6A was given soon after L-arginine, its effect on blood flow was not greater than that of L-arginine alone suggesting that L-arginine in a large amount makes guanylate cyclase less available for the more active peptide.

Platelet aggregation in platelet-rich plasma (PRP) is more sensitive to agonists and more resistant to antagonists than that in whole blood. In this study, we show that the presence of neutrophils in whole blood accounts at least in part for diminished platelet aggregation in whole blood. The platelet-inhibitory effect of neutrophils relates to the release of nitric oxide and not to elastase or adenosine. Furthermore, two unrelated platelet inhibitors, iloprost and tissue-type plasminogen inhibitor, decrease platelet aggregation to a greater extent in whole blood than in PRP. However, these agents exert cumulative or synergistic inhibitory effects with neutrophils on platelet aggregation in PRP. Thus, the inhibition of platelet aggregation in vivo may relate to the interaction between neutrophils and platelet-inhibitory agents.

To determine the effect of cholesterol incorporation on the ability of neutrophils to generate superoxide radicals and nitric oxide-like vasorelaxant material, isolated human neutrophils were incubated with cholesterol-rich liposomes, which increased total cholesterol content by 141% and esterified cholesterol content by 523%. Cholesterol loading resulted in 5 to 7 fold increase in cytosolic calcium in resting as well as in PMA or f-MLP-stimulated cells, but a marked (P less than 0.01) reduction in both PMA- and f-MLP-stimulated superoxide radical generation by these cells. Nitric oxide-like activity measured as relaxation of rat aortic rings was more pronounced (P less than 0.02) in cholesterol-rich than in cholesterol-poor cells. The greater relaxation of aortic rings in response to cholesterol-rich neutrophils was observed in rings with or without intact endothelium, and was potentiated by superoxide dismutase and inhibited by oxyhemoglobin as well as L-NMMA, thus suggesting that the vasorelaxant material was nitric oxide. The greater generation of nitric oxide by cholesterol-rich neutrophils occurs perhaps in response to increased cytosolic calcium.

Previous studies have indicated a possible role for polymorphonuclear leukocytes (PMNLs) in the maintenance of hemostasis and vascular tone. We now demonstrate that unstimulated isolated PMNLs maintained at 37 degrees inhibited human platelet aggregation in a concentration- and time-dependent fashion. In addition, PMNLs increased platelet cyclic GMP concentrations. The platelet aggregation inhibitory effect of PMNLs was potentiated by superoxide dismutase and attenuated by hemoglobin and methylene blue. This inhibitory effect of PMNLs was not observed in 48-hr-old killed cells and was not modulated by aspirin treatment or by adenosine deaminase. These observations suggest that human PMNLs maintained at 37 degrees produce a substance with biological characteristics similar to those of the endothelium-derived relaxing factor.

The superoxide radical scavenging effects of the SH group in the captopril molecule has been proposed to be the basis of the "cadioprotective" effect of this angiotensin converting enzyme (ACE) inhibitor in animal models of myocardial injury. We determined the effects of captopril, another ACE inhibitor with an SH group (SQ 26,703), its stereoisomer without ACE inhibitory effect but with an SH group (SQ 14,534), another ACE inhibitor without a SH group (enalaprilat), and N-acetylcysteine on superoxide radical generation by human neutrophils and by the purine-xanthine oxidase reaction. None of the compounds examined decreased superoxide radicals in therapeutic concentrations; however, SH-containing agents directly reduced spectrophotometric absorbance of ferricytochrome C. Thus, SH-containing agents with or without ACE inhibitory effects do not scavenge superoxide radicals.

The effects of isolated leukocytes (polymorphonuclear leukocytes [PMNLs] or neutrophils and lymphocytes) on platelet aggregation in platelet-rich plasma (PRP) were examined. Both PMNLs and lymphocytes decreased platelet aggregation in a concentration-dependent fashion. PMNL-induced, but not lymphocyte-induced, inhibition of platelet aggregation was more pronounced as the incubation time of PRP with PMNLs was prolonged. The platelet-inhibitory effect of PMNLs was enhanced by superoxide dismutase (SOD) and was attenuated by oxyhemoglobin and methylene blue. These agents, in contrast, had no effect on lymphocyte-mediated inhibition of platelet aggregation. Adenosine deaminase did not modulate the platelet inhibitory effects of either PMNLs or lymphocytes. The incubation of PMNLs with PRP was associated with an increase in cyclic guanine 5' monophosphate (cGMP) levels in PRP. Incubation of lymphocytes, however, did not result in an increase in cGMP levels in PRP. Neither PMNLs nor lymphocytes in PRP caused a reduction in thromboxane B2 (TXB2) or an increase in 6-keto-PGF1 alpha. Thus this study shows potent inhibitory effects of isolated PMNLs mediated by a substance with biologic characteristics of nitric oxide. However, the mechanism of lymphocyte-induced inhibition of platelets appears to be independent of prostaglandins, nitric oxide, or adenosine.

Release of superoxide radicals during the early phase of coronary reperfusion may result in degradation of endothelium-derived relaxing factor (EDRF), extension of myocardial injury, precipitation of arrhythmias, and stimulation of platelet aggregation. These factors may relate to the occurrence of ventricular fibrillation during reperfusion and coronary reocclusion following initial thrombolysis. This study was designed to examine the effects of concomitant administration of superoxide radical scavenger superoxide dismutase (SOD) with tissue plasminogen activator (tPA) compared to tPA alone (without SOD) in acute coronary thrombosis in anesthetized dogs. Dogs with a stable electrically induced coronary thrombus were randomly given intravenously tPA (0.75 mg/kg) alone or SOD bolus (2 mg/kg) followed by SOD (4 mg/kg) + tPA (0.75 mg/kg) over 20 min. tPA alone restored coronary blood flow in six of nine dogs (reperfusion rate of 67%) with time to reflow of 18.5 +/- 6.7 (mean +/- SD) min. Coronary reocclusion occurred spontaneously in four of six dogs with initial reperfusion (reocclusion rate of 67%). In contrast, SOD + tPA restored coronary blood flow in 9 of 12 dogs (reperfusion rate of 75%, not significant vs. tPA alone) with time to reflow of 11.3 +/- 4.8 min and coronary reocclusion occurred in only 3 of 9 dogs with reperfusion (reocclusion rate of 33%, not significant vs. tPA alone). Reperfusion arrhythmias were more frequent in dogs who received tPA alone compared to those who received SOD in addition to tPA (mean Holter-monitored PVC count of 730 vs. 12 beats/h, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Platelets play an important role in the formation of a coronary thrombus and reocclusion after thrombolysis. Therefore, we examined the thrombolytic potential of concomitant intravenous administration of potent platelet inhibitor iloprost, a prostacyclin analogue, with tissue-type plasminogen activator (t-PA; n = 8) and t-PA alone (n = 9) in dogs with an electrically induced occlusive coronary artery thrombus. t-PA (0.75 mg/kg) was given over 20 minutes, and iloprost (4 micrograms/kg) was given over 40 minutes. Reperfusion rate was 63% (five of eight dogs) in the t-PA plus iloprost group and 67% (six of nine dogs) in the t-PA alone group (p = NS). The time to thrombolysis (or reperfusion) in the t-PA plus iloprost group was almost twice as great as in the t-PA alone group (33.0 +/- 13.3 vs. 18.5 +/- 6.7 minutes, mean +/- SD, p less than 0.02), and the duration of reperfusion was much shorter (3.4 +/- 1.8 vs. 39.3 +/- 17.4 minutes, p less than 0.005). Peak coronary artery blood flow after reperfusion in the t-PA plus iloprost group was also less (20 +/- 17 ml/min) than in the t-PA alone group (58 +/- 21 ml/min, p less than 0.005). Reocclusion occurred in all dogs given t-PA with iloprost despite potent synergistic platelet inhibitory effects of t-PA and iloprost, whereas four of six dogs given t-PA alone reoccluded. Neither regimen exerted a significant beneficial effect on regional myocardial shortening during coronary reperfusion. Plasma levels of t-PA were lower when iloprost was given with t-PA (1,022 +/- 360 vs. 1,459 +/- 270 ng/ml in t-PA alone group, p less than 0.05). The detrimental effects of iloprost identified in this study may relate to the reduction in plasma t-PA concentrations by its degradation in the liver caused by the prostacyclin analogue iloprost.

Constriction of atherosclerotic coronary segments during exercise may further reduce coronary flow reserve in patients with coronary artery disease. This could influence the linear regression analysis of the heart rate-related changes in ST-segment depression (ST/HR slope) thereby limiting the accuracy of this method in identifying the severity of the disease. To test this hypothesis, the exercise related ST/HR slopes on placebo were compared with those obtained during coronary vasodilation induced by a prostacyclin analogue (iloprost 6 ng kg-1 min-1) in 42 anginal patients with documented coronary artery disease. In seven of these, the same protocol was repeated during right heart catheterization. The overall diagnostic accuracy of the ST/HR slope on iloprost was better than on placebo in patients with advanced coronary artery disease. This was due mainly to a consistent rightward shift of the ST/HR slope in patients with one- and two-vessel, but not three-vessel disease or left main stem disease. The reason for the greater effects of iloprost on ST/HR slopes in patients with a lesser degree of atherosclerosis remains unclear. However, coronary blood flow was higher during drug infusion, which suggests that iloprost may prevent the occurrence of dynamic coronary events able to reduce the maximum coronary flow reserve during exertion. This mechanism may be predominant in patients with minor coronary artery disease.