IL-1 and related cytokines enhance thrombin-stimulated PGI2 production in cultured endothelial cells without affecting thrombin-stimulated von Willebrand factor secretion or platelet-activating factor biosynthesis

We examined the effects of various cytokines on alpha-thrombin-stimulated prostaglandin (PG) I2 production, von Willebrand factor (vWF) secretion, and platelet-activating factor (PAF) synthesis in cultured human umbilical vein endothelial cells (HUVEC). A 24-h pretreatment with IL-1 beta doubled the low level of constitutive PGI2 production. In contrast, alpha-thrombin increased PGI2 production fivefold in untreated HUVEC. The most striking increase in PGI2 production was observed in IL-1 beta-treated HUVEC that were subsequently stimulated with thrombin. PGI2 production was two to three times greater than in untreated, thrombin-stimulated HUVEC and nearly eightfold greater than in IL-1 beta-treated but unstimulated HUVEC. Enhanced thrombin-stimulated PGI2 production was also observed in HUVEC pretreated with the related cytokines IL-1 alpha, TNF, or lymphotoxin. This cytokine effect was selective for PGI2 production because none of these cytokines altered either constitutive or thrombin-stimulated vWF secretion or PAF biosynthesis. IL-1 beta enhancement of thrombin-stimulated PGI2 production was concentration and time dependent and required protein synthesis. IL-1 beta pretreatment also enhanced PGI2 production in response to another agonist, histamine, and to exogenously added substrates, arachidonic acid or PGH2. Our results indicate that activation by IL-1 and related cytokines selectively primes endothelial cells for enhanced PGI2 production, but not vWF secretion or PAF synthesis, in response to thrombin and histamine. The evidence suggests that this effect is mediated through specific induction of biosynthetic enzymes for PGI2.     

Il-10 is a central regulator of cyclooxygenase-2 expression and prostaglandin production

IL-10 is a potent anti-inflammatory and immune regulatory cytokine. IL-10(-/-) mice produce exaggerated amounts of inflammatory cytokines when stimulated with LPS, indicating that endogenous IL-10 is a central regulator of inflammatory cytokine production in vivo. PGs are lipid mediators that are also produced in large amounts during the inflammatory response. To study the role of IL-10 in the regulation of PG production during the acute inflammatory response, we evaluated LPS-induced cyclooxygenase (COX) expression and PG production in wild-type (wt) and IL-10(-/-) mice. LPS-induced PGE(2) production from IL-10(-/-) spleen cells was 5.6-fold greater than that from wt spleen cells. LPS stimulation resulted in the induction of COX-2 mRNA and protein in both wt and IL-10(-/-) spleen cells; however, the magnitude of increase in COX-2 mRNA was 5.5-fold greater in IL-10(-/-) mice as compared with wt mice. COX-1 protein levels were not affected by LPS stimulation in either wt or IL-10(-/-) mice. Neutralization of IFN-gamma, TNF-alpha, or IL-12 markedly decreased the induction of COX-2 in IL-10(-/-) spleen cells, suggesting that increased inflammatory cytokine production mediates much of the COX-2 induction in IL-10(-/-) mice. Treatment of IL-10(-/-) mice with low doses of LPS resulted in a marked induction of COX-2 mRNA in the spleen, whereas wt mice had minimal expression of COX-2 mRNA. These findings indicate that, in addition to IL-10's central role in the regulation of inflammatory cytokines, endogenous IL-10 is an important regulator of PG production in the response to LPS.     

Synergistic increases in IL-1 synthesis by the human monocytic cell line THP-1 treated with PAF and endotoxin

The capacity to stimulate cytokine release may be important to the long-term effects of platelet-activating factor (PAF), which has a very short half-life. Previous studies have shown that PAF stimulates interleukin 1 (IL-1) release by human monocytes. IL-1 and other cytokines produced in response to PAF may be important to the long-term effects of this short-lived lipid. The THP-1 human monocytic leukemia cell line, was used to study the mechanism by which PAF stimulates IL-1 release. PAF stimulates the release of IL-1 beta activity into THP-1 cell supernatants with a multiphasic dose-response curve very similar to that for monocytes. When THP-1 cells are treated with PAF and LPS in combination, these two stimuli interact synergistically to greatly increase the release of IL-1 activity. To assess the effect of PAF on IL-1 beta synthesis, THP-1 cell pellet proteins were separated by SDS-PAGE, blotted, and immunostained to detect IL-1 beta. Immunostaining revealed that PAF increases intracellular IL-1 beta precursor and that the combination of PAF and LPS increases IL-1 beta precursor synergistically. PAF increases IL-1 beta release mainly by increasing IL-1 beta synthesis.     

Augmentation of ultraviolet B radiation-induced tumor necrosis factor production by the epidermal platelet-activating factor receptor.

Ultraviolet B radiation (UVB) has been shown to damage human keratinocytes in part by inducing oxidative stress and cytokine production. Indeed, UVB-induced production of the pro-inflammatory and cytotoxic cytokine tumor necrosis factor alpha (TNF-alpha) has been implicated in the epidermal damage seen in response to acute solar radiation. Though the lipid mediator platelet-activating factor (PAF) is synthesized in response to oxidative stress, and keratinocytes express PAF receptors linked to cytokine biosynthesis, it is not known whether PAF is involved in UVB-induced epidermal cell cytokine production. These studies examined the role of the PAF system in UVB-induced epidermal cell TNF-alpha biosynthesis using a novel model system created by retroviral-mediated transduction of the PAF receptor-negative human epidermal cell line KB with the human PAF receptor (PAF-R). Treatment of PAF-R-expressing KB cells with the metabolically stable PAF-R agonist carbamoyl-PAF resulted in increased TNF-alpha mRNA and protein, indicating that activation of the epidermal PAF-R was linked to TNF-alpha production. UVB irradiation of PAF-R-expressing KB cells resulted in significant increases in both TNF-alpha mRNA and protein in comparison to UVB-treated control KB cells. However, UVB treatment up-regulated cyclooxygenase-2 mRNA levels to the same extent in both PAF-R-expressing and control KB cells. Pretreatment with the antioxidant vitamin E or the PAF-R antagonists WEB 2086 and A-85783 inhibited UVB-induced TNF-alpha production in the PAF-R-positive but not control KB cells. These studies suggest that the epidermal PAF-R may be a pharmacological target for UVB in skin.     

Biphasic platelet-activating factor synthesis by human monocytes stimulated with IL-1-beta, tumor necrosis factor, or IFN-gamma

The capacity of IL-1-beta, TNF, and IFN-gamma to stimulate platelet-activating factor (PAF) synthesis by human monocytes is examined in our report. All three cytokines induced PAF synthesis in a novel biphasic pattern with peaks of PAF synthesis 1 to 2 and 6 to 8 h after stimulation of the monocytes. In contrast, calcium ionophore A23187 elicited a single peak of early PAF synthesis. PAF in the early peak was largely retained intracellularly whereas PAF in the late peak was largely released into culture fluids. Combinations of cytokines were subadditive or antagonistic in inducing PAF synthesis. Cycloheximide inhibited the late peak of PAF synthesis indicating that protein synthesis is required for synthesis of the phospholipid PAF. Specific antibodies to TNF or IL-1-beta inhibited the late peak of PAF synthesis induced by IFN-gamma indicating that late PAF synthesis is dependent on cytokine synthesis. The quantities of PAF produced by cytokine-activated monocytes are sufficient to activate human monocytes. Thus, these studies suggest that PAF may mediate in part monocyte activation by cytokines.     

A serine proteinase inhibitor isolated from Tamarindus indica seeds and its effects on the release of human neutrophil elastase

Proteinaceous inhibitors with high inhibitory activities against human neutrophil elastase (HNE) were found in seeds of the Tamarind tree (Tamarindus indica). A serine proteinase inhibitor denoted PG50 was purified using ammonium sulphate and acetone precipitation followed by Sephacryl S-300 and Sephadex G-50 gel filtration chromatographies. Inhibitor PG50 showed a Mr of 14.9 K on Sephadex G-50 calibrated column and a Mr of 11.6 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. PG50 had selective activity while cysteine proteinases (papain and bromelain) and serine proteinases (porcine pancreatic elastase and bovine chymotrypsin) were not inhibited, it was strongly effective against serine proteinases such as bovine trypsin and isolated human neutrophil elastase. The IC50 value was determined to be 55.96 microg.mL-1. PG50 showed neither cytotoxic nor haemolytic activity on human blood cells. After pre-incubation of PG50 with cytochalasin B, the exocytosis of elastase was initiated using PAF and fMLP. PG50 exhibited different inhibition on elastase release by PAF, at 44.6% and on release by fMLP, at 28.4%. These results showed that PG50 preferentially affected elastase release by PAF stimuli and this may indicate selective inhibition on PAF receptors.     

Increased production of the ether-lipid platelet-activating factor in intestinal epithelial cells infected by Salmonella enteritidis

When exposed to enteric pathogens intestinal epithelial cells produce several cytokines and other proinflammatory mediators. To date there is no evidence that the ether-lipid platelet-activating factor (PAF) is one of these mediators. Our results revealed a significant increase in PAF production by human colonic tissue 4 h after infection by enterohemorrhagic Escherichia coli (EHEC) or Salmonella enteritidis. PAF is produced in the gut by cells of the immune system in response to bacterial infection. To determine whether the epithelial cells of colonic mucosa might also modulate PAF levels, we carried out PAF quantification and analysis of the enzymes involved in PAF synthesis in 5-day-old (undifferentiated) or 28-day-old (differentiated) Caco-2 cell cultures. Infection of undifferentiated Caco-2 cells with either bacterium had no effect on PAF levels, whereas in differentiated cells, infection by S. enteritidis increased PAF levels. Following infection by S. enteritidis, there were no changes in the activity of dithiothreitol-insensitive choline phosphotransferase. However, the enzymes of the remodeling pathway cytosolic phospholipase A(2), which catalyzes the formation of the PAF precursor lysoPAF, and lysoPAF acetyltransferase, are activated in the infected epithelial cells. This response is Ca(2+)-dependent.     

Synthesis of platelet-activating factor (PAF) in transformed cell lines of a different origin

Interest in the possible involvement of the platelet-activating factor (PAF) in tumor growth and invasiveness has been stimulated by the recognition that PAF influences various biological responses relevant to metastatic diffusion, such as angiogenesis, adhesiveness to endothelia and cellular motility. In the present study, we investigated the extent to which PAF is synthesized by a series of human and murine transformed cell lines of a different histotype. Synthesis of PAF was studied by combining the 14C-acetate incorporation into PAF with the quantitative analysis of PAF performed by a procedure based on gas chromatography-mass spectrometry with a negative ion chemical ionization. In the presence of the Ca2+ ionophore A23187, cultures of human melanoma (Hs294T), fibrosarcoma (HT1080) and colon carcinoma (LS180) cell lines synthesized conspicuous amounts of PAF, comparable to those produced by resident peritoneal macrophages. Substantial quantities of PAF were also synthesized by the murine melanoma (F10-M3 cells). PAF synthesis was rather limited in RSV-transformed Balb/c3T3 (B77-3T3) cells and in one of their high metastatic variants (B77-AA6 cells), although it was more abundant in the latter. We also investigated whether certain cytokines, such as TNFalpha and IFNgamma might induce PAF synthesis in our systems of cell lines which we found to express mRNAs encoding receptors for these cytokines. We observed that PAF synthesis was enhanced in human melanoma and colon carcinoma cell lines and in the murine B77-AA6 cells to levels comparable to those obtained with the Ca2+ ionophore. Synthesis of PAF was not inducible by TNFalpha in murine F10-M3 melanoma cells. IFNgamma also stimulated PAF synthesis in human and murine melanoma lines, and in human LS180 colon carcinoma line, but not in the B77-AA6 cells. PAF synthesis was also inducible by exogenous PAF in the human and murine melanoma lines, and in the human LS180 colon carcinoma line, all of which expressed cell surface PAF receptors. PAF synthesis was not inducible by exogenous PAF in the B77-AA6 cells, which do not express PAF receptors.     

In vitro prostaglandin release from and platelet-activating factor accumulation in isolated endometrial cells from pregnant and pseudopregnant rabbits.

Prostaglandin (PG) release from and platelet-activating factor (PAF) accumulation by enzymatically isolated endometrial epithelial and stromal cells from Day 6 pregnant and Day 6 pseudopregnant rabbits were studied in vitro, using RIA for PG measurement and a platelet aggregation assay for PAF measurement. On the first day of culture in serum-free media, PGF release into the medium was significantly higher from epithelial cells from Day 6 of pregnancy than from stromal cells from Day 6 of pregnancy or pseudopregnancy. PGE release did not differ significantly among these cell types. The addition of indomethacin (10(-5) M) to similar cultures inhibited release of both PGs from both cell types, but to a much greater extent from stromal than from epithelial cells. Significant stimulation of PG release by A23187 was achieved under all conditions on the fifth day of culture; PGE release was significantly greater than PGF release from stromal cells from Day 6 of pregnancy and pseudopregnancy, and release of both PGs from stromal cells was significantly greater from Day 6 of pregnancy than from Day 6 of pseudopregnancy. PG release from similar cells, cultured in medium containing 10% calf serum, was highest on the first or second day of culture and then, especially for PGF, declined with continued culture. PGE release was significantly higher than PGF release from stromal cells on the third and fourth days of culture. The ratios of PGF/PGE release from epithelial cells were significantly higher than those from stromal cells over the 5-day culture period for both reproductive stages. These ratios indicate the differential release of PGE and PGF from rabbit endometrial cell subpopulations and indicate a preferential release of PGE from stromal and of PGF from epithelial cells. Under basal conditions, PAF was not detected in epithelial or stromal cells cultured for 2 or 4 days, or in the associated culture media. If PAF had been released into the medium, it would have rapidly metabolized. Short exposure to calcium ionophore A23187 (10(-5) M) was able to stimulate PAF accumulation in epithelial and stroma cells in serum-free media, probably via the remodeling pathway. PAF was not detected in the medium. Intracellular PAF accumulation after exposure to A23187 (10(-5) M) for 5 min was significantly greater on the second day of culture than on the fourth day in epithelial and stromal cells from Day 6 of pregnancy.(ABSTRACT TRUNCATED AT 400 WORDS)     

Release of proinflammatory cytokines related to luteolysis and the periparturient acute phase response in prostaglandin-induced parturition in cows

An acute phase response was previously found in cows at parturition, which might be associated with uterine cytokine release. Five late pregnant cows were implanted with vascular catheters in both the maternal aorta and uterine vein. Blood samples were taken to study temporal relationships between changing plasma levels of proinflammatory cytokines and the periparturient acute phase response following prostaglandin (PG)-induced luteolysis at Day 275 of gestation. The plasma levels of three proinflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) and interleukin-6 (IL-6), as well as progesterone (P4), PGFM and serum amyloid A (SAA) were measured every 4 h between PG induction and expulsion of the calf. In the arterial plasma, progesterone levels dropped to baseline levels within 10 h following PG treatment, indicative of complete luteolysis. Contrary to expectations, the uterine vein samples showed lower proinflammatory cytokine levels compared with the maternal aorta values. A classical acute phase response, as assessed by SAA, was observed during the expulsive stage, but not during luteolysis.     

Platelet-activating factor induces mediator release by human basophils primed with IL-3, granulocyte-macrophage colony-stimulating factor, or IL-5.

The phospholipid platelet-activating factor (PAF) is a potent cell-derived bioactive molecule thought to be involved in diverse inflammatory processes. It has been shown that PAF can activate different leukocyte types and platelets, particularly in synergy with other agonists. In this study we examined the effect of PAF upon the release of histamine and leukotriene (LT) C4 by basophils when added alone and in combination with different agonists and cytokines. PAF by itself did neither induce histamine release nor the generation of LTC4 by basophils. However, basophils primed by the hematopoietic growth factors (hGF) IL-3, granulocyte-macrophage (GM)-CSF, or IL-5 (10 ng/ml) released preformed and de novo synthesized mediators in response to PAF at 10 to 100 nM concentrations. The extent of mediator release by hGF primed basophils in response to PAF was similar to that induced by an optimal concentration of monoclonal anti-IgE. Thus, similar to NAP-1/IL-8 and C3a, PAF efficiently stimulates mediator release in hGF-primed basophils only. However, PAF was clearly a more potent trigger of LTC4 formation in IL-3-primed cells than NAP-1/IL-8 or C3a. When PAF was used as a second trigger, the priming effect of IL-5 was less than that of IL-3 or GM-CSF, whereas the response for other IgE-independent agonists (i.e., C5a or FMLP) was augmented equally by all three hGF. IL-1 beta-pretreated basophils released minimal amounts of histamine in response to PAF. Neither TNF-alpha nor PAF, nor the combination thereof, was able to induce basophil mediator release. The efficiency of the different cytokines to prime for PAF responsiveness was strikingly similar to their capacity to enhance anti-IgE-induced mediator release. Similar to other IgE-independent agonists, the kinetic of mediator release in response to PAF was very rapid. PAF pretreatment of basophils did not enhance mediator release in response to diverse agonists, such as C5a and FMLP, in contrast to the capacity of PAF to augment the response of other leukocyte types to appropriate stimuli. Thus, depending on the presence of IL-3, GM-CSF, or IL-5, PAF is a potent basophil agonist capable of inducing histamine release as well as de novo synthesis of LTC4.     

Cytokine regulation of adult human osteoblast-like cell prostaglandin biosynthesis

Prostaglandin (PG) biosynthesis by cytokine stimulated normal adult human osteoblast-like (hOB) cells was evaluated by thin layer chromatography, high performance liquid chromatography, and specific immunoassays. PGE₂ was the predominant PG formed under all incubation conditions tested. Control samples produced measurable amounts of PGE₂, and the measured level of this metabolite increased by 22-fold (from 7 to 152 ng/ml) following a 20 h treatment with the combination of TGFβ and tumor necrosis factor-α(TNF). The production of 6-keto-PGF_1α (the stable metabolite of prostacyclin) and of PGF_2α were each increased by about five-fold (from about 0.5 to 2.5 ng/ml) in samples treated with the cytokines. Thus, TGFβ and TNF exerted a regulation of hOB cell PG biosynthesis that was principally directed towards an increased PGE₂ biosynthesis, with lesser effects on the production of other PG metabolites. COX-2 mRNA levels were increased within 2 h of cytokine stimulation, reached a maximum at 6–12 h, and levels had appreciably diminished by 24 h after treatment. Both TGFβ and TNF could independently increase COX-2 mRNA levels and PG biosynthesis. However, the increased production of PGE₂ resulting from TNF stimulation was blocked by the addition of an interleukin-1β (IL-1β) neutralizing antibody, suggesting that TNF regulation of hOB cell PG synthesis was secondary to its capacity to increase hOB cell IL-1β production. TGFβ regulation of PG production was not affected by the addition of the neutralizing antibody. These studies support the proposition that PGs can be important autocrine/paracrine mediators of bone biology, whose production by hOB cells is responsively regulated by osteotropic cytokines. J. Cell. Biochem. 64:618–631. © 1997 Wiley-Liss, Inc.     

Platelet-activating factor stimulates production of prostaglandin E2 in murine osteoblast-like cell line MC3T3-E1.

We found that platelet-activating factor (PAF) stimulated the production of prostaglandin (PG) E2 in MC3T3-E1 cells in a time- and dose-dependent manner. 1.0 microM PAF gave a maximal stimulation of PGE2 production by MC3T3-E1 cells after a 4 hr PAF-treatment. Furthermore, the PAF-induced PGE2 production was abolished by the pre-treatment of the cells with a PAF receptor antagonist, 1-O-hexadecyl-2-acetyl-sn-glycero-3-phospho(N,N,N-trimethyl)hexanolamine, which occupied the same receptor site as PAF. These results suggest that PAF stimulates the PGE2 synthesis through a PAF receptor mediated pathway. Possibly PAF modulates bone metabolism by stimulating PGE2 synthesis.     

The effects of platelet-activating factor on the output of prostaglandins from the guinea-pig uterus

Platelet-activating factor (PAF) significantly increased the output of prostaglandin (PG) F2 alpha from the guinea-pig uterus during the mid-cycle phase (Days 6-10), but only had a small, non-significant stimulatory effect on the outputs of PGE2 and 6-keto-PGF1 alpha. PAF significantly increased the outputs of PGF2 alpha, PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus during the later phase of the cycle (Days 15-17). Lack of extracellular calcium did not affect the stimulatory effect of PAF on uterine PG output. However, TMB-8 (an intracellular calcium antagonist) prevented the increases in uterine PG output produced by PAF at both phases of the cycle. These results suggest that the stimulatory effect of PAF on uterine PG output in the guinea-pig is dependent upon the mobilization of intracellular calcium but is not dependent upon the uptake of extracellular calcium. Also, the weak stimulatory effect of PAF on PGE2 output from the uterus during the mid-cycle phase indicates that, if PAF is involved in implantation in guinea-pigs, it probably does not act via PGE2. Also, the lack of an inhibitory effect of PAF on uterine PGF2 alpha synthesis and release suggests that PAF is not the anti-luteolytic factor produced by the guinea-pig conceptus during early pregnancy.     

Platelet-activating factor (PAF) is the effector of IFN gamma-stimulated invasiveness and motility in a B16 melanoma line

In this study, we investigated whether PAF synthesized by F10-M3 cells (a clone of B16-F10 melanoma line) mediates the increased capacity of these cells to penetrate into Matrigel upon stimulation with IFN gamma. The determination of PAF synthesized by IFN gamma-stimulated tumor cells revealed that 70% of newly synthesized PAF was released into growth media, while the remaining 30% was associated with the cell bodies. An experimental protocol based on the use of WEB 2086, a PAF receptorial antagonist, was designed to explore which of the two fractions of PAF synthesized by IFN gamma-stimulated F10-M3 cells (released into the growth medium or associated with the cell bodies) is essential to their capacity to migrate through Matrigel. We found that the PAF secreted into growth medium is the fraction responsible for the enhanced invasiveness of melanoma cells stimulated with IFN gamma. We also investigated whether motility of melanoma cells is stimulated by IFN gamma, and, if so, whether PAF is involved in this effect. We found that WEB 2086 prevented the remodeling of stress fibers, examined as an index of cell motility, that we observed in F10-M3 cells stimulated with IFN gamma. Furthermore, the observation that PAF receptor is expressed in IFN gamma-stimulated melanoma cells suggests that the invasive phenotype (e.g. migration through a reconstituted basement membrane and motility) promoted by PAF is based on an autocrine mechanism. On the whole, these results might indicate that PAF contributes to the expression of properties typical of an invasive phenotype in tumor cells stimulated with cytokines.     

Adhesion-independent synergy of monocytes and endothelial cells in cytokine production: regulation of IL-6 and GM-CSF production by PAF

Co-Cultures of monocytes (MO) and endothelial cells (EC) were studied for their capacity to synergize in the production of interleukin-6 (IL-6) and granulocyte-macrophage colony-stimulating factor (GM-CSF), two cytokines potentially important in vascular physiopathology. Resting monocytes produced detectable amounts of IL-6 but no GM-CSF, whereas confluent EC produced significant quantities of GM-CSF, but minimal IL-6. In co-cultures without stimuli, additive synthesis of both cytokines was observed. When EC were pretreated, however, with either PAF, TNF or both stimuli, before addition of MO, synergistic production of IL-6 was observed. In contrast, GM-CSF production was not enhanced by coculture of monocytes with activated EC. When either cell population was fixed with paraformaldehyde or killed by freeze-thawing before addition to the co-culture, cytokine levels reverted to those produced by the unaffected population alone. On the other hand, separating the two cell populations by a cell-impermeable membrane in transwell cultures did not affect the synergistic production of the cytokines. Taken together, our data suggest that EC and MO can synergize in response to stimuli by producing IL-6 and that this synergy is dependent on the integrity of both cell populations, but independent of cell-cell contact.     

Platelet-activating factor and cardiac diseases: therapeutic potential for PAF inhibitors

Platelet-activating factor (PAF) is a potent phospholipid mediator released from inflammatory cells in response to diverse immunologic and non-immunologic stimuli. Animal studies have implicated PAF as a major mediator involved in coronary artery constriction, modulation of myocardial contractility and the generation of arrhythmias which may bear on cardiac disorders such as ischemia, infarction and sudden cardiac death. PAF effects are induced by direct actions of PAF on cardiac tissue to modify chronotropic and inotropic activity, or indirectly via the release of eicosanoids such as thromboxane A₂ (TXA,), leukotrienes (LT) or cytokines (TNFx). The development of selective, high affinity PAF receptor antagonists has permitted investigations on the role of PAF in experimental animal models of cardiac injury. In vivo and in vitro studies strongly suggest that PAF receptor antagonists might convey therapeutic benefits in ischemic conditions and certain arrhythmias. In addition, PAF antagonists might have a cardiac allograft-preservation effect. Although clinical studies with PAF receptor antagonists in patients with cardiac diseases have not yet been reported, the experimental results to date suggest that PAF receptor antagonist might be useful in some specific cardiac disorders in humans.