In vivo complement activation by polyanion--polycation complexes: evidence that C5a is generated intravascularly during heparin--protamine interaction

Prostacyclin, cardiopulmonary bypass and the alveolar capillary membrane

In a double blind controlled study of 24 patients undergoing coronary artery bypass grafting, 12 received an infusion of prostacyclin at 20 ng/kg/min during cardiopulmonary bypass in an attempt to reduce the previously reported increased alveolar capillary membrane permeability that occurs postoperatively. Prostacyclin significantly reduced platelet activation but had no effect in reducing complement activation or transpulmonary neutrophil sequestration. Alveolar epithelial permeability as assessed by measuring the clearance of inhaled 99mTc-DTPA from lung to blood did not change postoperatively in either group.

In order to fully evaluate pulmonary damage following cardiopulmonary bypass a marker for pulmonary endothelial damage may need to be used.

Enhancement of the leukocyte-endothelial cell interaction in collecting venules of skeletal muscle by protamine

OBJECTIVE

A transient but severe systemic leukopenia regularly occurs after the antagonization of heparin by protamine in patients and in animals. The aim of the present study was to investigate the site and mechanisms of white blood cell retention during this transient leukopenia by studying the leukocyte-endothelial cell interaction in skeletal muscle venules.

METHODS

Syrian golden hamsters were equipped with a dorsal skinfold chamber for intravital fluorescence microscopy and arterial and venous catheters for drug infusion, blood pressure measurement, and blood sampling. Microhemodynamic parameters and leukocyte-endothelial cell interactions were observed in one single collecting venule per animal after intravenous infusion of saline solution (control, n = 10), of protamine (n = 9), and after infusion of heparin followed by either intravenous protamine (n = 9) or intraarterial protamine (n = 9).

RESULTS

All parameters remained unchanged in the control group. Whereas venular diameters remained unchanged, protamine transiently increased arterial blood pressure and venular erythrocyte velocity in all groups. Systemic leukocyte counts and the venular leukocyte discharge concentration decreased concurrently after protamine administration by about 60% to 70% at 2 minutes while the fraction of rolling leukocytes and the number of adherent leukocytes remained unchanged. Two and one-half minutes later, systemic leukocyte counts and venular discharge concentrations normalized while the fraction of leukocytes rolling slowly along or adhering firmly to the venular endothelial wall increased considerably and similarly in all groups receiving protamine. Myeloperoxidase (an indicator of polymorphonuclear leukocytes) determination in 20 separate hamsters 2 minutes after protamine infusion revealed increased myeloperoxidase activity exclusively in the lungs.

CONCLUSION

The response of leukocytes to protamine infusion with or without prior heparinization is biphasic: initial retention of leukocytes in the lungs is followed by enhanced leukocyte-endothelial cell interaction in the systemic circulation.

Effective and less toxic reversal of low-molecular weight heparin anticoagulation by a designer variant of protamine

PURPOSE

This investigation assessed protamine reversal of heparin anticoagulation by formation of a protamine-heparin alpha-helix by use of a new designer-variant protamine [+18BE] that was made from an existing protamine variant [+18B] whose non-alpha-helix-forming amino acid proline (P) was replaced by an alpha-helix-forming glutamic acid (E). The rate of administration of the new [+18BE] variant protamine on efficacy and toxicity in comparison to that of [+21] standard protamine and [+18B] was also studied.

METHODS

Acetyl-EAA(K2A2K2A)4K2-Amide [+18BE] was administered intravenously in a 1:1 dose to low-molecular-weight heparin (LMWH)-anticoagulated (intravenous 150 IU antifactor Xa/kg) dogs over 10 seconds or 3 minutes (n = 7, each group). Reversal efficacy was documented by measuring activated clotting time, thrombin clotting time, antifactor Xa, and antifactor IIa. Toxicity was defined by measuring systemic blood pressure, heart rate, cardiac output, pulmonary artery pressure, and oxygen consumption. Measurements were made at baseline, after administration of LMWH, before its reversal, and for 30 minutes thereafter. Results were compared with those after LMWH reversal with [+21] standard protamine and the [+18B] variant. A total toxicity score (TTS) was calculated for each compound from maximal declines in blood pressure, heart rate, cardiac output, and oxygen consumption.

RESULTS

LMWH anticoagulation reversal was significantly (p < 0.01) less toxic over 10 seconds and 3 minutes with the [+18BE] designer variant (TTS -2.3, -2.2) compared with the [+21] standard protamine (TTS -6.4, -7.2). Percent LMWH reversal at 3 minutes revealed [+18BE] to have antifactor Xa activity as high as 91%, compared with 68% for protamine [+21], when given over 3 minutes (p < 0.05).

CONCLUSIONS

This investigation documents that a new designer variant of protamine [+18BE] has superior efficacy compared with [+21] standard protamine for reversal of LMWH anticoagulation and that this occurs with a highly favorable toxicity profile.

Heparin and protamine use in peripheral vascular surgery: a comparison between surgeons of the Society for Vascular Surgery and the European Society for Vascular Surgery

It was the intent of this study to document, in general, the patterns and complications of heparin and protamine usage during carotid endarterectomy, aortic and femoral-popliteal-tibial reconstructions for occlusive disease, elective and emergent abdominal aortic aneurysmectomy, thromboembolectomy, and dialysis arteriovenous (AV) fistula placement by surgeons from North America and Europe. All vascular surgeons from the Society for Vascular Surgery (SVS) and the European Society for Vascular Surgery (ESVS) were surveyed by a voluntary, self-reported questionnaire. Six hundred and forty-six completed questionnaires (284 from SVS and 362 from ESVS), representing a 62% response rate, were returned for evaluation. Systemic and regional administration of heparin was common during vascular procedures performed by both SVS and ESVS surgeons. Use of protamine to reverse heparin anticoagulation varied among SVS and ESVS surgeons, respectively, during: carotid endarterectomy (54% vs. 26%, p < 0.01), elective aortic reconstruction for occlusive disease (58% vs. 23%, p < 0.001), elective aortic reconstruction for abdominal aortic aneurysm (63% vs. 27%, p < 0.001), and femoral-popliteal-tibial reconstruction (44% vs. 15%, p < 0.001). Adverse reactions to protamine among the 25,219 and 12,902 cases reported from SVS and ESVS surgeons, respectively, included: hypotension (1209 and 495 cases), pulmonary artery hypertension (65 and eight cases), anaphylaxis (52 and 10 cases), and death (seven and two cases). These adverse responses accounted for 5.3% and 4.0% of the SVS and ESVS cases, respectively. Although this study is subject to the known limitations of a retrospective survey, it is clear that heparin use is common. Protamine reversal of heparin anticoagulation is more common in North America.(ABSTRACT TRUNCATED AT 250 WORDS)

Inflammatory response to cardiopulmonary bypass

Cardiac operations with cardiopulmonary bypass cause a systemic inflammatory response, which can lead to organ injury and postoperative morbidity. Causative factors include surgical trauma, contact of blood with the extracorporeal circuit, and lung reperfusion injury on discontinuing bypass. Advances in immunological techniques have allowed measurement of both plasma and intracellular components of this multifaceted perioperative response. This includes activation of the complement, coagulation, fibrinolytic, and kallikrein cascades, activation of neutrophils with degranulation and protease enzyme release, oxygen radical production, and the synthesis of various cytokines from mononuclear cells (including tumor necrosis factor, interleukin-1, and interleukin-6). Advances in our understanding of the interactions between these markers of cellular and humoral responses to cardiopulmonary bypass will enable more effective intervention to reduce the deleterious effects and improve the outlook for patients undergoing cardiac operations beyond the 1990s.

Absence of complement-mediated events after protamine reversal of heparin anticoagulation

Protamine reversal of heparin anticoagulation is associated with adverse hemodynamic effects that may be attenuated with protamine pretreatment (PP). This study assesses the role of complement activation during these phenomena in adult cardiac surgery patients. Sixteen individuals undergoing cardiopulmonary bypass were given intravenous normal saline or protamine (2 mg/kg) as a randomized pretreatment prior to undergoing heparin anticoagulation (400 IU/kg), coronary artery revascularization, and subsequent reversal of the anticoagulated state with protamine (4 mg/kg). Blood pressure, pulmonary artery diastolic pressure (PAD), heart rate, and cardiac output (CO) were measured during and after pretreatment, prior to heparin reversal by protamine, and for 10 min after reversal. Total hemolytic complement (CH50), C3 conversion to C3b, C3a/C5a, platelet count, and white blood cell count (WBC) were also measured at the same time periods. No significant correlation existed between complement activation and hemodynamic events, as might have been evident by decreased CH50, increased C3 conversion to C3b, or elevations in C3a/C5a levels. PP significantly prevented the CO decrease occurring at 1 and 3 min following heparin reversal by protamine (-0.8 and -1.4 liters/min vs 0.1 and -0.2 liters/min, P less than 0.05 and P less than 0.01, respectively). Reversal hypotension was less with PP, although PAD fell equally in both groups. WBC decreases after heparin reversal were less after PP (-25% vs -7%, P = 0.06). These data support the conclusion that, contrary to earlier reports, adverse hemodynamic and hematologic responses accompanying protamine reversal of heparin anticoagulation do not appear to be correlated with activation of complement. In fact, those patients having the greatest C3a generation exhibited the least hemodynamic changes.

Diagnostic significance of hypocomplementemia

Hypocomplementemia is an important marker for the presence of IC-mediated disease and can be used to assess disease activity. However, in interpreting the clinical significance of hypocomplementemia, the following must be kept in mind: 1) There are numerous non-immunologic conditions that also can cause hypocomplementemia. Furthermore, some of these conditions can cause a multisystem disease that, along with the hypocomplementemia, can closely resemble an IC-mediated systemic vasculitis. Furthermore, these nonimmunologic conditions that lower serum complement levels can complicate the course of patients with inactive IC-mediated disease, spuriously indicating that the disease is active. The most relevant of these differential diagnostic problems are listed in Table 2. 2) There are a few conditions (for example, pregnancy) that can raise serum complement levels, thereby possibly obscuring the presence of a disorder (such as, active SLE) that is lowering complement levels. 3) There are some conditions that might be expected to lower serum complement levels, because of their effect on protein metabolism, but do not. Nephrotic syndrome, and moderately poor nutrition are examples. All of these factors should be considered when interpreting results of serum complement levels in a given patient.

Neutralization of low molecular weight heparin by polybrene prevents thromboxane release and severe pulmonary hypertension in awake sheep

Protamine reversal of heparin anticoagulation in patients is occasionally associated with life-threatening acute pulmonary hypertension. In a sheep model, we evaluated the effect on this adverse cardiopulmonary reaction of modifying the type of heparin (low molecular weight heparin compared with unfractionated heparin) and the type of heparin antagonist (polybrene compared with protamine). Protamine reversal of low molecular weight heparin (LMWH) and polybrene reversal of unfractionated heparin induced more than a 10-fold increase of plasma thromboxane B2 levels, a threefold increase of pulmonary vascular resistance and pulmonary artery pressure, and a 25% decrease of PaO2. A similar adverse reaction followed protamine reversal of conventional unfractionated heparin. However, with polybrene (1 mg/kg) reversal of LMWH (1 mg/kg), we measured neither pulmonary hypertension (pulmonary artery pressure was 22.6 +/- 3.6 mm Hg at 1 minute after polybrene reversal of LMWH compared with 47.9 +/- 4.2 mm Hg after protamine reversal of unfractionated heparin, p less than 0.005 groups differ), hypoxemia (PaO2 was unchanged 2 minutes after polybrene compared with a decrease of 26 mm Hg 2 minutes after protamine, p less than 0.05), nor acute release of thromboxane into arterial plasma (thromboxane B2 was 0.2 +/- 0.1 at 1 minute after polybrene compared with 3.7 +/- 1.7 ng/ml at 1 minute after protamine, p less than 0.005). The hemodynamic effects and mediator release were also benign after neutralization of larger doses of LMWH (3 mg/kg) by polybrene (3 mg/kg). The increases of activated clotting time and activated partial thromboplastin time due to both types of heparin were completely reversed with polybrene. Anti-Xa activity increased to more than 3 IU/ml 4 minutes after LMWH anticoagulation (p less than 0.01) but was only partially neutralized by polybrene. Various polyanion-polycation complexes that are formed when heparin anticoagulation is reversed induce thromboxane release and acute pulmonary vasoconstriction in awake sheep. Reversal of LMWH anticoagulation with polybrene does not elicit this adverse reaction.

Thromboxane receptor blockade prevents pulmonary hypertension induced by heparin-protamine reactions in awake sheep

We used competitive thromboxane A2-prostaglandin endoperoxide receptor blockade (SQ 30,741) as a probe to evaluate the role of thromboxane in ovine pulmonary vasoconstriction associated with protamine reversal of heparin anticoagulation. Control heparin-protamine reactions induced rapid release of thromboxane into arterial plasma (more than 1 ng/ml plasma), a 2.5-fold increase of pulmonary artery pressure, a 20% decrease of PaO2, and a 30% reduction in arterial white blood cell concentration. After giving SQ 30,741 despite similar thromboxane release into arterial plasma after heparin-protamine challenge, acute pulmonary hypertension was significantly reduced when 94% of pulmonary vascular smooth muscle thromboxane receptors were occupied with SQ 30,741 (p less than 0.01 at 1 minute after protamine versus control heparin-protamine reaction) and was completely abolished by a 10 mg/kg i.v. bolus (p less than 0.0001 at 1 minute after protamine versus control). Peripheral leukopenia was not affected by SQ 30,741 prophylaxis, but hypoxemia was prevented. We conclude that thromboxane causes pulmonary vasoconstriction in ovine heparin-protamine-induced pulmonary hypertension. Pulmonary vasoconstriction and hypoxemia can be completely prevented by thromboxane receptor blockade.

Pathophysiology of cardiopulmonary bypass: current issues

Much of the research related to cardiopulmonary bypass in recent years has been directed toward defining the changes in plasma and blood cells during bypass. In this review, recent information is reexamined for six areas of current interest. These areas are complement activation, immune response, anaphylactic reactions, coagulation, and cerebral dysfunction. Complement may be activated by either the classical or alternate pathway during cardiopulmonary bypass and protamine administration. Membrane oxygenators appear to diminish the degree of complement activation. Complement is a major factor in the whole body inflammatory response; which often accompanies cardiopulmonary bypass. A product of complement activation, C5a- desArg, causes activation and aggregation of granulocytes. Other products of complement activation lead to lysis of blood cells including granulocytes and red cells. Bubble oxygenators appear to have a distinct disadvantage compared to membrane oxygenators regarding infection. Airborne microorganisms are more likely to be entrained into circulating blood with bubble oxygenators than with membrane oxygenators. Bubble oxygenators cause a greater decrease in leukocyte number and function than membrane oxygenators. Anaphylactic reactions have been associated with use of antibiotics, blood products, protamine, and volume expanders during cardiopulmonary bypass. Protamine reactions may be on an immunological basis or due to direct toxicity of the drug. Free radicals including superoxide, hydrogen peroxide, and the hydroxyl radical may be generated during cardiopulmonary bypass and reperfusion. Free radical scavengers including; vitamin E, coenzyme Q, vitamin C, mannitol, and glutathione have been studied. The avoidance of blood transfusion because of risk of transmitted infection including AIDS has become a major goal in cardiac surgery. Factors that correlate with increased transfusion requirement include low hematocrit, female gender, increased age, small body size, low ejection fraction, reoperation, and emergency operation. Heparin resistance due to antithrombin III deficiency is being recognized more commonly. Antithrombin III deficiency may be corrected with fresh frozen plasma. Patients with heparin induced thrombocytopenia may be difficult to manage. Several management protocols are suggested. The most straightforward appears to be the use of aspirin preoperatively and platelet transfusions postoperatively. The incidence of cerebral dysfunction after cardiopulmonary bypass depends on the sensitivity of the test or indicator used. Perioperative stroke is associated with intrinsic cerebrovascular disease and atherosclerosis of the ascending aorta. Retinal angiograms during cardiopulmonary bypass show that microemboli are very common. Cerebroplegia has been shown to extend the period of safe circulatory arrest in animals. Much of the new knowledge concerning cardiopulmonary bypass is the result of close collaboration between cardiac surgeons and nonsurgical scientists.

A prospective study of the risk of an immediate adverse reaction to protamine sulfate during cardiopulmonary bypass surgery

Protamine sulfate administration may cause life-threatening reactions. We prospectively examined the incidence of immediate adverse reaction after protamine in 243 patients who underwent cardiopulmonary bypass surgery. Twenty-six patients (10.7%) had reactions, and 1.6% had a precipitous drop in blood pressure immediately after protamine administration. Risk factors were previous exposure to protamine, diabetes, history of receiving protamine-containing insulin, and possibly vasectomy. However, neither a positive skin test nor a positive IgE ELISA for antiprotamine antibody predicted that a patient would have a reaction. C4a levels were increased in patients who had reactions as compared with age-, sex-, and cardiac disease-matched patients who did not have reactions, suggesting a role for complement in some reactions. Immediate adverse reactions to protamine are very common, and alternative therapies are urgently needed to eliminate the use of protamine.

Cardiac anaphylaxis. Complement activation as an amplification system

Complement is activated, and C3a and C5a anaphylatoxins are generated during hypersensitivity reactions clinically associated with cardiopulmonary collapse. The administration of C3a or C5a to nonsensitized isolated guinea pig hearts mimics the events caused by antigen challenge of sensitized hearts (i.e., cardiac anaphylaxis) in the absence of complement. Thus, complement-derived anaphylatoxins may participate in immediate hypersensitivity reactions in which the heart is a target organ. To assess the contribution of complement activation and anaphylatoxin generation to cardiac dysfunction, we have elicited anaphylaxis in isolated guinea pig hearts in the presence of complement and found that the ensuing dysfunction is markedly enhanced. This amplification is most likely attributable to anaphylatoxin formation because 1) inactivation of C3 or selective C3 depletion, i.e., the loss of the component responsible for the formation of the anaphylatoxins C3a and C5a, prevents complement-induced exacerbation of cardiac anaphylaxis, whereas reconstitution with C3 and C5, or even only C3, restores it; in fact, the greater the C3 content at the time of antigen challenge, the more intense the anaphylactic crisis; and 2) the severity of cardiac anaphylaxis is markedly reduced by preexposure to C3a, and this reduction is directly related to the dose of C3a injected and to the amount of endogenous cardiac histamine depleted by C3a before antigen challenge. Complement-derived anaphylatoxins appear to promote the same mediator release that has been initiated by the antigen-antibody reaction; thus, complement activation functions as an amplification system in cardiac anaphylaxis.

Lack of cross-reactivity between IgE to salmon and protamine sulfate

Immediate type-generalized reactions to protamine sulfate are uncommon but may be fatal. The mechanisms of severe or fatal reactions are unknown in most cases. One theory is that contaminating fish (salmon) proteins present in protamine solutions induce anaphylaxis in salmon-sensitive subjects. A second hypothesis is that protamine interacts with anti-salmon IgE to cause anaphylaxis. We assessed these hypotheses by establishing an indirect amplified enzyme-linked immunosorbent assay (ELISA) for IgE to salmon. Sera obtained from two subjects anaphylactically sensitive to salmon demonstrated high binding to salmon that was not inhibited by preincubation of sera with 500 or 1000 micrograms of protamine or Aspergillus fumigatus. Serum from a patient who experienced anaphylactic shock from protamine was indistinguishable from control sera in the ELISA for IgE to salmon. Anti-protamine IgE could not be demonstrated in separate experiments. The assays prove that 1) serum IgE to salmon is not inhibited by protamine and 2) serum from a patient experiencing a severe reaction to protamine did not contain IgE to salmon or protamine. The experiments do not support the notion that there is cross-reactivity between IgE to salmon and protamine sulfate in the cases evaluated.

Complement activation from protamine sulfate administration after coronary angiography

The cause of hypotension after reversal of heparin by protamine has not been well defined. In this study we evaluated complement activation (C3a and C4a) by the heparin-protamine complex in 46 consecutive patients (40 received protamine sulfate to reverse heparin, and six did not) during and after coronary angiography. In patients receiving protamine sulfate, there was a significant increase in C3a over the value before protamine sulfate administration (P less than .001) or in patients who did not receive protamine sulfate (P less than .05): 807 +/- 100 ng/ml vs. 274 +/- 75 ng/ml. There were no significant changes in C4a after protamine sulfate administration. These results indicate that the alternate complement pathway is activated when protamine sulfate is administered after coronary angiography. This may induce hypotension as well as platelet aggregation and thrombus formation and may contribute to coronary instability. Therefore, in unstable patients, heparin reversal by protamine should not be done routinely.

Complement depletion and persistent hemodynamic-hematologic responses in protamine-heparin reactions

Hypotension, bradycardia, pulmonary artery hypertension, neutropenia, and thrombocytopenia have been suspected to be due to complement activation following protamine reversal of heparin. This investigation examined these phenomena in complement-depleted animals. Eight dogs received intraperitoneal naja n. naja cobra venom factor (CVF), 20 U/kg, 48 and 24 hr prior to anticoagulation with sodium heparin, 150 IU/kg, and reversal 30 min later with protamine sulfate, 1.5 mg/kg. Decomplementation was confirmed in all dogs. Systemic blood pressure (BP), pulse (HR), pulmonary artery systolic and diastolic pressures, (PAS, PAD), cardiac output (CO), platelet count (PTC), and white blood count (WBC) with differential were monitored. The maximal mean changes for the entire group were BP, -43 mm Hg; HR, -16; PAS, +6 mm Hg; PAD, +3 mm Hg; CO, -27%; PTC, -49%; and WBC, -48%. These hemodynamic and hematologic responses, occurring in the face of CVF-induced decomplementation, support the conclusion that complement components C3 and C5-C9 are not influential factors contributing to these protamine-heparin-induced events.

The myocardial contractile responses to protamine sulfate and heparin

The administration of protamine sulfate for the reversal of heparin anticoagulation has been associated with adverse hemodynamic changes including hypotension and decreased cardiac output. The possible direct toxic effect of protamine on human right atrial trabeculae contracting isometrically in vitro was studied. Muscles were stimulated to contract at 1 Hz in Tyrode's solution (maintained at 34 degrees C, pH 7.4) into which protamine was continuously added. Following a polynomial regression analysis, a parabolic dose-response curve resulted. The equation was: y = 95.13 + 38.76x - 278.71x2 where y = relative developed force and x = concentration of protamine (milligrams per milliliters) (r = 0.82). The estimated concentration of protamine resulting in 50% developed force was 0.48 mg/ml. In a second series of experiments, protamine was added to the bath along with a neutralizing amount of heparin. This resulted in a limited reduction in the fall of relative developed force. Thus, protamine in high concentrations alone or in complex with heparin has a direct toxic effect on human myocardial muscle mechanics, and care is warranted in its clinical use.

Haemodynamic and haematologic alterations with protamine reversal of anticoagulation: comparison of standard heparin and a low molecular weight heparin fragment

Reversal of anticoagulation with protamine sulfate causes many adverse haemodynamic and haematologic effects which could be due to differences in the mechanism of action of standard and low molecular weight heparin. Three groups of dogs were investigated: one group received normal saline pretreatment followed by heparinisation with standard heparin 150 IU/kg followed by protamine sulfate reversal 1.5 mg/kg after aortic interposition grafting: the second group were given normal saline pretreatment followed by heparinisation with low molecular weight heparin 150 U antiXa/kg and after grafting protamine sulfate reversal 1.5 mg/kg. The third group were given protamine sulfate pretreatment 2.25 mg/kg followed by low molecular weight heparin 150 U antiXa/kg and later protamine sulfate reversal 1.5 mg/kg after grafting. The same haemodynamic changes were seen regardless of the type of heparin or pretreatment with protamine given along with low molecular weight heparin. There was a suggestion that regular heparin cause a more pronounced increase in pulmonary artery pressure and a decrease in heart rate. On the other hand the systemic hypotension and reduction of cardiac output seemed more pronounced in the low molecular weight heparin group. Platelet count decreased less in the low molecular weight heparin group, but white blood cell count was equally reduced. Pretreatment with protamine did not abolish the adverse effects of protamine when reversing anticoagulation achieved with low molecular weight heparin, a finding not shared with standard heparin-protamine interactions.

Cardiac dysfunction caused by purified human C3a anaphylatoxin

The purpose of this investigation was to define the cardiac effects of complement-derived C3a anaphylatoxin, in view of the possibility that cardiac dysfunction may occur as a result of complement activation. Purified human C3a was administered by intracoronary bolus injections into isolated guinea pig hearts. As a function of dose, C3a caused tachycardia, impairment of atrioventricular conduction, left ventricular contractile failure, coronary vasoconstriction, and histamine release. These effects were abolished by cleavage of the COOH-terminal arginine by carboxypeptidase B. The magnitude of C3a-induced tachycardia correlated with the amount of endogenous cardiac histamine released into the coronary effluent. Whereas the tachycardia was markedly reduced by the histamine H2 antagonist cimetidine, the contractile failure and the coronary vasoconstriction caused by C3a were antagonized by the leukotriene antagonist FPL 55712 and by the cyclooxygenase inhibitor indomethacin, respectively. This suggests that histamine, leukotrienes, and vasoactive prostanoates may mediate the various cardiac effects of C3a. Our findings indicate that C3a anaphylatoxin has marked cardiac effects at concentrations that are likely to be attained with a degree of C3 activation commonly seen in various disease states. Thus, our data are compatible with the hypothesis that generation of anaphylatoxins may induce cardiac dysfunction in clinical conditions.