Experimental Cardiac Transplantation Research Articles

Tacrolimus Regulates MicroRNAs in Recipient Immune Cells after Experimental Cardiac Transplantation

Tacrolimus Regulates MicroRNAs in Recipient Immune Cells after Experimental Cardiac Transplantation

Clinical Heart Transplantation With Extended Preservation Time (>5 Hours): Experience With University of Wisconsin Solution

Use of University of Wisconsin solution has been suggested for extended organ preservation >4 hours in experimental cardiac transplantation, but few data have been reported from clinical use. This study investigated the impact of preservation with UW solution after prolonged ischemic times on myocardial damage and outcomes after heart transplantation. Between 1994 and 2006, 34 orthotopic heart transplantations were performed at our institution with cold ischemic times of >or=300 minutes (mean, 325.1 +/- 21.3). Donor organs were perfused with and stored in 1000 mL of University of Wisconsin solution. No significant differences were observed with regard to age, gender, diagnosis, donor inotropic support, and donor-recipient weight ratio when compared with recipients undergoing an ischemic time <300 minutes. After a mean follow-up of 47.6 months (range, 1 day to 147.1 months), Kaplan-Meier survival analysis revealed survivals of 91.0% at 3 months, and 82.9% for the entire observation period. The time required to wean from bypass (mean, 78.1 minutes) was equal when compared with that of recipients experiencing grafts undergoing an ischemic time of <300 minutes, but there was a significantly greater average need for inotropic support over the first 48 posttransplant hours. Neither hospital stay in the ICU (mean, 13.0 days; range, 1-55 days) nor the incidence of acute graft failure or survival was different. We conclude that heart preservation with UW limited ischemic damage from prolonged storage and improved myocardial function in the early posttransplant period, thus allowing transplantation of organs with ischemic times >300 minutes.

Age-dependent Chronic Rejection After Experimental Heart Transplantation

The progressive decline of allograft function is predominantly a consequence of chronic rejection, but the etiology of this process is not fully understood. To evaluate the influence of age we performed heart transplantation in an experimental model of chronic rejection using inbred rats of different age. Lewis rats served as donors and F344 rats were used as recipients. Young rats were 4 weeks of age, whereas adult rats were 4 months of age. Transplanted animals were grouped as follows: Group I, old to old; Group II, old to young; Group III, young to old; and Group IV, young to young. Intra-abdominal heterotopic heart transplantation was performed. Thereafter, functional evaluation was performed by daily palpation and surface electrocardiogram (ECG) to calculate the functional heart rejection index (fHRI). One month after transplantation the hearts were explanted and examined pathohistologically. Functional deterioration was noted in all groups, but all hearts were still beating when explanted. Young recipients and young donors showed significantly better results. Transplantation of young recipients led to a better fHRI (p < 0.001) and to a less critical chronic graft vasculopathy, especially when there was a young heart transplanted (p = 0.03). Furthermore, whenever a young donor heart was used, there was a better graft performance and less severe chronic rejection (p = 0.02). Experimental cardiac transplantation of young hearts leads to a better graft performance as well as to a lower incidence of a severe chronic graft disease. Thus, older donor age may adversely influence long-term performance of cardiac allografts.

Transplante experimental cardíaco heterotópico e cutâneo em camundongos

Objective: This is an experimental study which aims at developing and evaluating the feasibility of experimental techniques of vascularized and cutaneous abdominal heterotopic heart transplant in mice, creating an instrument of investigation for the effectiveness of prservation solutions, Experimental heterotopic cardiac and cutaneous transplantation in mice

The immunosuppressant FK778 shows favourable drug interactions with tacrolimus and mycophenolate mofetil in experimental cardiac transplantation

Objectives: The goal of the study was to investigate combination regimens of FK778 with tacrolimus (Tac) and mycophenolate mofetil (MMF) in a high-responder rat cardiac transplantation model.

Combination regimens of FK778 with tacrolimus and mycophenolate mofetil in experimental cardiac transplantation

were primary immunized with influenza vaccine 7-9 weeks prior to transplant in absence of immunosupression. A secondary boost immunization was administered during therapy with either IDEC-131 monotherapy (n 4), or CyA (controls, n 2). at day 14 post transplant. The antibody responses was measured against two influenza epitopes (H1N1, H3N2). Results: 5 out of 6 animals responded to the primary flu challenge by the production of IgM (5) and IgG (4). Despite intact primary responses, CyA completely abrogated the secondary Ab response in both animals. In contrast, all anti-CD154-treated animals (4/4) mounted a secondary IgM Ab response. The secondary IgG response was modulated by anti-CD154 blockade: absent in 2 animals, weak in 1, and robust in 1. Conclusion: As opposed to CyA, which completely inhibits the secondary response to influenza, CD154 blockade did not impair the ability of the graft recipient to mount a secondary response against influenza. If confirmed in a larger series and in the setting of chronic illness, this finding suggests that CD154 blockade spares important facets the recipients adaptive immunity against opportunistic infections, potentially conferring a clinically significant advantage over conventional immunosuppression with respect to common pathogens.

CD26/DPP IV in experimental and clinical organ transplantation.

The T-cell activation-Ag CD26 possesses dipeptidyl peptidase IV (DPP IV) enzymatic activity. Costimulatory efficacy and immunocompetence are associated with the enzymatic activity. In models of experimental cardiac allograft transplantation (HTx), we analyzed the role of CD26/DPP IV during organ rejection. Also, we investigated CD26 enzymatic and cellular expression in human recipients of kidney transplants (Tx). Heterotopic HTx in rats, models of acute and accelerated rejection. Monitoring of DPP IV serum levels and humoral immunity. Propro-diphenyl phosphonate was employed to inhibit DPP IV activity during rejection. In a prospective study, surface expression of CD26, 3, 4, 8, 45, 122 and ADA on PBL and DPP IV serum activity were measured in kidney recipients for 24 months post-transplantation. Acute rejection was . associated with increased serum DPP IV activity (p < 0.005). Specific inhibition abrogated acute (p < 0.0001) and accelerated (p < 0.01) rejection, impairing cytotoxicity and allospecific Ig-synthesis. Kidney recipients displayed a significant drop in CD26 expression on PBL for up to 18 months postoperatively (p < 0.001). CD4, 8, 45, 122 and ADA expression kinetics were only briefly affected. DPP IV enzymic activity stayed depressed for at least 12 months (p < 0.001). CD26/DPP IV is pivotal in T-cell mediated immune responses toward allo-Ag. In clinical transplantation, engraftment/immunosuppression are reflected by CD26 cellular and enzymatic expression posttransplantation and may serve as an indicator for immunomodulation.

Two good reasons for an angiotensin-II type 1 receptor blockade with losartan after cadiac transplantation: reduction of incidence and severity of transplant vasculopathy

Abstract Despite considerable progress in immunosupressive therapy, the incidence and severity of transplant vasculopathy (TVP) after cardiac transplantation have not declined. The renin-angiotensin system (RAS) plays a pivotal role in the proliferation of vascular smooth muscle cells (VSMCs) contributing to TVP. We compared the effects of an angiotensin-II blocker, losartan (AT1 blocker), and an angiotensin-converting enzyme (ACE) inhibitor, enalapril, on the incidence of diseased vessels and the severity of experimental TVP in the Lewis-to-Fischer rat heterotopic heart transplantation model. Recipients were randomly divided into six groups, group 1: no therapy, group 2: 3 mg/kg per day cyclosporine (CyA) s.c., group 3: CyA and 10 mg/kg per day losartan p.o., group 4: CyA and 40 mg/kg per day enalapril p.o., and groups 5 and 6: as groups 3 and 4, but additionally pre-treated with losartan or enalapril 7 days prior to transplantation. Eighty days after grafting, we assessed the incidence and severity of TVP, expressed as percentage of diseased vessels and mean vessel occlusion (MVO), by digitizing morphometry. CyA and CyA/enalapril post-treatmet significntly reduced MVO, compared with controls, but not the incidence. Additional reduction of MVO was achieved in CyA/enalapril pre-treatment and both CyA/losartan pre-and post-treatment groups when compared with CyA and untreated controls. However, only losaran post-treatment in combination with CyA reduced both incidence and MVO. Our reults validate the important role of the RAS in neointimal proliferation after cardiac transplantation. Losartan appears to be superior to enalapril in preventing TVP after experimental cardiac transplantation. Therefore, AT1 blockade with losartan might be a theraputic option for the prevention of TVP in human heart recipients.

Two good reasons for an angiotensin-II type 1 receptor blockade with losartan after cardiac transplantation: reduction of incidence and severity of transplant vasculopathy.

Despite considerable progress in immunosuppressive therapy, the incidence and severity of transplant vasculopathy (TVP) after cardiac transplantation have not declined. The renin-angiotensin system (RAS) plays a pivotal role in the proliferation of vascular smooth muscle cells (VSMCs) contributing to TVP. We compared the effects of an angiotensin-II blocker, losartan (AT(1) blocker), and an angiotensin-converting enzyme (ACE) inhibitor, enalapril, on the incidence of diseased vessels and the severity of experimental TVP in the Lewis-to-Fischer rat heterotopic heart transplantation model. Recipients were randomly divided into six groups, group 1: no therapy, group 2: 3 mg/kg per day cyclosporine (CyA) s.c., group 3: CyA and 10 mg/kg per day losartan p.o., group 4: CyA and 40 mg/kg per day enalapril p.o., and groups 5 and 6: as groups 3 and 4, but additionally pre-treated with losartan or enalapril 7 days prior to transplantation. Eighty days after grafting, we assessed the incidence and severity of TVP, expressed as percentage of diseased vessels and mean vessel occlusion (MVO), by digitizing morphometry. CyA and CyA/enalapril post-treatment significantly reduced MVO, compared with controls, but not the incidence. Additional reduction of MVO was achieved in CyA/enalapril pre-treatment and both CyA/losartan pre- and post-treatment groups when compared with CyA and untreated controls. However, only losartan post-treatment in combination with CyA reduced both incidence and MVO. Our results validate the important role of the RAS in neointimal proliferation after cardiac transplantation. Losartan appears to be superior to enalapril in preventing TVP after experimental cardiac transplantation. Therefore, AT(1) blockade with losartan might be a therapeutic option for the prevention of TVP in human heart recipients.

The impact of CD4 and CD8 transendothelial migration in the development of transplant arteriosclerosis following experimental cardiac transplantation

Purpose: Chronic rejection after transplantation is characterized by vascular smooth muscle cell (VSMC) migration and proliferation in the subintimal space. This activation of VSMC could be mediated by transendothelial migration of CD4 and CD8 positive (1) leucocytes. The objective of this study was to test the ability of CSA, FK-506 and MMF to reduce the transendothelial migration of CD41 and CD81 leukocytes in correlation with the resulting neointimal proliferation. Methods: After heterotopic cardiac transplantation from Lewis to Fisher rats animals were divided into four therapygroups of therapy: CSA 3mg/kg/d (n574), MMF 40 mg/kg/d (n596), FK-506 0.03 mg/kg/d (n596) and a control group receiving no immunosuppressive therapy (n574). 3-4 animals of each group were sacrificed in intervals of 1-4 days up to day 60. Immunohistochemistry was performed using mAb against CD4 and CD8 and positive cells were analysed at the endothelium and in the perivascular space of intra (s)and epicardial (L) arteries. Statistical analysis was performed using the areas under the curves over the time of 60 days by an extended t-test. Results: CSA, FK-506 and MMF reduced CD4 and CD8 positive leukocytes at the endothelium and in the perivascular space (PVS) of s and L arteries, as well as they reduced neointimal proliferation of the arteries, compared with the control group. MMF significantly reduced CD41 cells in the PVS of s and L arteries compared with FK-506 and CSA treated groups (p,0.05). We found no significant difference between FK-506 and CSA, neither in the reduction of the CD41 cells nor in the extent of chronic rejection. MMF significantly reduced neointimal proliferation compared with FK-506 and CSA. There was a significant correlation between the CD41 cells in the PVS and the resulting neointima but no with the CD81 cells in the PVS. Conclusion: MMF attenuates transendothelial migration of CD41 leucocytes and reduced chronic rejection. Immunosuppression with MMF after cardiac transplantation seems to be an option to prevent chronic rejection.

Preconditioning prevents myocardial stunning after cardiac transplantation

Background. Preconditioning has been shown to reduce myocardial stunning after reversible global ischemia. To determine whether preconditioning improves functional recovery after cardiac transplantation, 16 sheep were randomly assigned to a preconditioning protocol or to a control group.Methods. Preconditioning was achieved with 5 minutes of global ischemia followed by 10 minutes of reperfusion. The heart was then arrested with 1 L of crystalloid cardioplegia, explanted, stored in a transport cooler, and then transplanted into recipient sheep. The total ischemia time was 2 hours. Pressure-volume loops were used to calculate preload recruitable stroke work, the maximum elastance, and diastolic compliance. Linear regression analysis was used to determine the preload recruitable stroke work, maximum elastance, and diastolic compliance–and end-diastolic volume relationship. The area under the regression curve for preload recruitable stroke work was defined as the preload recruitable stroke work area. Biopsies were taken for high-energy phosphates.Results. Systolic function, represented by preload recruitable stroke work area, was preserved after cardiac transplantation in preconditioned animals. Maximum elastance and diastolic compliance were unaffected by preconditioning or ischemia. High-energy phosphates were better preserved in preconditioned animals.Conclusion. Preconditioning prevented myocardial stunning and preserved high-energy phosphates after experimental cardiac transplantation.

Editorial: Cardiac transplantation for auxiliary circulatory support

In this issue, Khaghani and associates report their experience with heterotopic cardiac transplantation in infants and children. This study is a welcome addition to the literature from the group at Harefield, which has assembled an extensive experience with this procedure. The concept of using the transplanted heart as an auxiliary pump was introduced in 1964.1Reemtsma K The heart as a test organ in transplantation studies.Ann NY Acad Sci. 1964; 120: 778-785PubMed Google Scholar, 2McGough EC Brewer PL Reemtsma K The parallel heart: studies of intrathoracic auxiliary cardiac transplants.Surgery. 1966; 60: 153-158Google Scholar These studies demonstrated that the auxiliary heart, placed in parallel with the animal's own heart, could sustain the circulation when the native heart was nonfunctional. This concept of assisted circulation now has been widely applied in the use of mechanical support, such as ventricular assist devices. It has been applied sporadically in clinical cardiac transplantation, and this report summarizes the experience in infants and children. The authors report that in a total of 1278 cardiac transplants, 104 (8.1% of the total experience) were placed in the intrathoracic, heterotopic position. This report focuses on 12 infants and children, nine of whom survive. The indications that the authors cite are (1) presence of fixed high pulmonary vascular resistance, (2) availability of undersized donors, and (3) the expectation of a degree of recipient heart recovery. It is encouraging that all patients showed a decrease in pulmonary artery pressure and all showed a normal growth pattern. It seems probable that the application of auxiliary cardiac support, both with transplants and with mechanical devices, will continue. The use of this approach for transplantation into patients with high, fixed pulmonary vascular resistance seems established. The further development of ventricular assist devices similarly will usually use this approach in preference to in situ replacement of the heart. Its usefulness in treating patients with reversible myocardial disease is intriguing but not yet established. The increasingly severe shortage of donor hearts has resulted in the use of marginally acceptable organs, and the use of such transplants as auxiliary pumps has certain advantages. Similarly, as cardiac xenografts approach clinical use, the auxiliary position rather than in situ replacement has appeal in this experimental area with uncertain outcome. Finally, a comment about nomenclature: The term heterotopic is nonspecific and refers to placement of the heart in any abnormal position. In the literature of experimental cardiac transplantation, heterotopic often refers to cervical or abdominal placement of the heart. The term piggyback is flippant and should be discarded. I recommend the terms auxiliary and parallel, as used in the original publications of this technique. These terms appropriately describe the function of the transplant, which supplements cardiac function by working in parallel with the native heart.

Elastase and cell matrix interactions in the pathobiology of vascular disease.

Ultrastructural observations in lung tissue implicated an endogenous vascular elastase (EVE), in the pathobiology of pulmonary vascular disease. In experimental rats, increased activity of a 20 kDa serine proteinase related to adipsin precedes the development of sustained pulmonary hypertension and vascular abnormalities. A further increase in activity is related to malignant progression of the disease. A cause and effect relationship was suggested by studies in which elastase inhibitors successfully prevented or retarded progression of pulmonary hypertension. In vitro studies have shown that both serum and endothelial factors induce EVE via tyrosine kinase intracellular signalling. Induction of EVE can release basic fibroblast growth factor from the extracellular matrix in an active form stimulating smooth muscle cell proliferation. Elastase activity was also observed in the process of smooth muscle cell migration and neointimal formation in coronary arteries following experimental cardiac transplantation. An immune/inflammatory response is observed with increased production of cytokines, tumor necrosis factor-alpha and interleukin (IL)-1 beta, reciprocally up-regulating production of fibronectin, a glycoprotein which mediated smooth muscle cell migration. The action of IL-1 beta in inducing fibronectin is facilitated by the production of elastin peptides generated by increased activity of an elastase in the coronary arteries. Our studies suggest that ligation of the elastin binding protein by elastin peptides unmasks IL-1 receptors. Fibronectin also stimulates transendothelial migration of lymphocytes which perpetuates the inflammatory response leading to neointimal formation in this model. Masking integrins on T cells with a decoy synthetic CS-1 (fibronectin) peptide largely prevented transendothelial migration and coronary neointimal formation following cardiac transplant.

The role of experimental aluminum intoxication in allogeneic immunoresponse

Abstract To evaluate the immunological properties of aluminum (Al) in experimental Al intoxication in rats, we performed heart transplantation and in vitro experiments. Lewis (Lew) rats were intoxicated with intraperitoneal injections of AlCl3. Heart transplants were performed using Brown-Norway (BN) rats as donors. Isotransplants and normal Lew were used as controls. No differences in survival were observed. Unidirectional mixed lymphocyte cultures (MLC) and Concanavalin A (Con A)-stimulated cultures were prepared using spleen cells from normal and Al-intoxicated Lew rats. No differences were found in unidirectional MLC. Intoxicated cells showed a less intense response to Con A than did normal cells. In conclusion, we could not detect an immunosuppressive role of Al intoxication in experimental cardiac transplantation or in MLC. However, the depressed Con A blastogenic response of Al-intoxicated cells may reflect an immunological role yet to be defined.

The role of experimental aluminum intoxication in allogeneic immunoresponse.

To evaluate the immunological properties of aluminum (Al) in experimental Al intoxication in rats, we performed heart transplantation and in vitro experiments. Lewis (Lew) rats were intoxicated with intraperitoneal injections of AlCl3. heart transplants were performed using Brown-Norway (BN) rats as donors. Isotransplants and normal Lew were used as controls. No differences in survival were observed. Unidirectional mixed lymphocyte cultures (MLC) and Concanavalin A (Con A)-stimulated cultures were prepared using spleen cells from normal and Al-intoxicated Lew rats. No differences were found in unidirectional MLC. Intoxicated cells showed a less intense response to con A than did normal cells. In conclusion, we could not detect an immunosuppressive role of Al intoxication in experimental cardiac transplantation or in MLC. However, the depressed Con A blastogenic response of Al-intoxicated cells may reflect an immunological role yet to be defined.

Chronic rejection in experimental cardiac transplantation in a rat model

The most significant pathologic finding in chronically rejected organ grafts is diffuse concentric intimal proliferation in the arterial system. To develop a reproducible model of chronic vascular rejection in cardiac grafts which we could then use to study the pathogenesis and therapy of this disease process, we exchanged heterotopic cardiac allografts across minor histocompatibility barriers using commercially available Lewis rats as donors and F‐344 rats as recipients. We found that all long‐term surviving allografts developed diffuse graft arteriosclerotic lesions which were virtually identical in appearance to those seen in chronically rejected human cardiac grafts. Immunohistochemical studies confirm that end‐stage lesions arc similar in composition to human lesions and are made up predominantly of vascular smooth muscle cells with occasional monocytes and T cells. Analysis of continuous series of rejecting allografts demonstrates that a distinct inflammatory stage precedes smooth muscle cell accumulation in areas of intimal thickening, suggesting that mononuclear cells play a role in the developing lesion. Endothelial expression of class II and ICAM‐1 probably underlies early mononuclear cell adherence to the endothelium. Analysis using quantitative RT‐PCR and immunocytochemistry confirms MCP‐I is expressed by ED I‐positive monocyte/macrophages in rejecting cardiac grafts, suggesting this chemoattractant may help drive mononuclear cell accumulation in the expanding intima. Immunohistochemical labelling of PDGF, TNF and IL‐1β in vascular lesions suggests these factors may trigger intimal vascular smooth muscle cell proliferation in chronically rejecting allografts, as they, along with protein S, were closely associated with sites of intimal hyperplasia and smooth muscle cell proliferation. Hypercholesterolemia did not enhance the severity of lesion development in long‐term surviving allografts, suggesting that lipid levels are not a major etiologic factor in graft arteriosclerotic lesion formation in the Lewis‐F‐344 model. Placing the recipients on a diet deficient in essential fatty acids (which modulates leukocyte functions and infiltration) reduced graft infiltration by mononuclear cells and markedly diminished arterial lesion development in chronically rejecting grafts. A key role for CD4 and mononuclear cells (T cells and/or macrophages) in the initiation and amplification of the vascular response is suggested because a short course of CD4 mAb‐ targeted therapy attenuated many of the vascular sequelae of chronic allograft rejection; there was an absence of myocardial necrosis, a lack of upregulation of ICAM and class II MHC antigens, and decreased expression of TNF, IL‐Iβ, TGF‐β, PDGF and protein S expression. Our data suggest that the activated macrophage is a major force in driving the system toward accelerated atherosclerosis, and that this model should prove useful in analyzing the pathogenesis and drug therapy of chronic rejection.

Chronic Rejection in Experimental Cardiac Transplantation: Studies in the Lewis‐F344 Model

Despite recognition of chronic vascular injection by numerous investigators since the beginning of experimental and solid organ transplantation, the pathogenesis of graft arteriosclerosis remains poorly understood. We have defined a reproducible model of this disease by transplanting heterotopic cardiac grafts across minor histocompatibility barriers using inbred strains of rat. We found that long-term surviving Lewis grafts in untreated F344 recipients are subjected to a chronic rejection process which results in the development of diffuse graft arteriosclerotic lesions, indistinguishable in appearance from those seen in human cardiac grafts. Immunohistochemical studies confirm that end-stage lesions are similar in composition to human lesions, made up predominantly of vascular smooth muscle cells with occasional monocytes and T cells. Analysis of serial rejecting allografts demonstrates that a distinct inflammatory stage precedes smooth muscle cell accumulation in areas of intimal thickening, suggesting that mononuclear cells play a role in the developing lesion. Endothelial expression of class II and ICAM-1 appears to lead to early mononuclear cell adherence to the endothelium. Analysis using quantitative RT-PCR confirms that MCP-1 is expressed by ED1-positive monocyte/macrophages in rejecting cardiac grafts, suggesting that this chemoattractant may help drive mononuclear cell accumulation in the expanding intima. Immunohistochemical labelling of PDGF, TNF, and IL-1 in vascular lesions suggests that these growth factors may trigger intimal vascular smooth muscle cell proliferation in chronically rejecting allografts. Hypercholesterolemia did not enhance the severity of lesion development in long-term surviving allografts, suggesting that lipid levels are not a major etiologic factor in graft arteriosclerotic lesion formation in the Lewis-F344 model. Finally, the dietary manipulation of EFAD reduced graft infiltration by mononuclear cells and markedly diminished arterial lesion development in chronically rejecting grafts. Heparin anologues have previously been shown to inhibit proliferative vascular smooth muscle cell lesions in rats following endothelial injury (Clowes & Karnovsky 1977), and we are currently assessing the role of heparin in the therapy of graft arteriosclerosis in the Lewis-F344 model. We are also investigating the role of CD4-positive mononuclear cells in the pathogenesis of lesion development, using the anti-CD4 monoclonal antibody BWH-4 to deplete recipients of CD4-positive cells (Sayegh et al. 1991). In summary, our studies in the Lewis-F344 model suggest that monocyte/macrophages play an important role in the pathogenesis of cardiac graft arteriosclerosis. Future studies utilizing this model should help further elucidate the mechanisms resulting in--and help define potential therapies for--chronic rejection in cardiac transplantation.

Current Issues in Clinical and Experimental Cardiac Transplantation

Cardiac transplantation is now an accepted therapy for end-stage heart failure not amenable to usual medical or surgical therapy. Despite excellent survival, important unresolved problems remain. This review focuses on current issues in cardiac transplantation. These controversial areas of active interest include the relationship between histocompatibility matching and the results of transplantation, the causes and treatment of graft coronary arteriopathy, and the mechanism of reversible heart failure that is caused by reversible transplant rejection. These fascinating unresolved issues remain significant challenges to those involved in the care of heart transplant recipients. Their resolution will improve significantly the results of this form of therapy.

A new technique of experimental heterotopic cardiac transplantation

Heterotopic cardiac transplantation is a useful method for studying allograft rejection. In this study a new technique of cardiac transplantation was carried out, which involved retroperitoneal anastomoses of the donor ascending aorta and main pulmonary artery with the recipient abdominal aorta and inferior vena cava respectively. The procedure was simple and effective and was accomplished with minimal operative mortality and postoperative morbidity. The method allows better access to the allograft for repeated open myocardial biopsies, obviating the limitations of transvenous fluoroscopically directed endomyocardial biopsy. This technique of retroperitoneal heterotopic cardiac transplantation has important advantages compared with similar procedures performed in the neck, abdomen, or thorax.

The effect of prednisolone, thromboxane, and platelet-activating factor receptor antagonists on lymphocyte and platelet migration in experimental cardiac transplantation.

Three agents that significantly prolong cardiac allograft survival were tested in Lewis rats that were recipients of hearts from Lewis X Brown-Norway F1 hybrid donors. In the presence of azathioprine, the effects of daily administration of either the thromboxane antagonist (L 640,035), the platelet-activating factor (PAF) antagonist (BN 52021) or prednisolone were evaluated on the infiltration of cardiac allografts by syngeneic lymphocytes and platelets labeled with 111indium. As anticipated, platelet deposition was reduced by the thromboxane antagonist and unaffected by the PAF antagonist; the latter is likely due to the known absence of PAF receptors in rat platelets. In addition prednisolone had no effect. The increased accumulation of lymphocytes on days 4-5 was also unaffected by all three drugs. These experiments indicate that, in this model, graft survival is not necessarily related to lymphocyte and platelet infiltration of the graft. The data also provide evidence for the efficacy of the thromboxane receptor antagonist L 640,035 in preventing platelet deposition in vivo.