The immunosuppressive effects of a leukotriene B4 receptor antagonist on liver allotransplantation in rats

The immunosuppressive effects of a leukotriene B₄ (LTB₄) receptor antagonist, ONO4057, on liver allotransplantation in rats were evaluated, and the levels of prostaglandin E₂ (PGE₂) in the liver tissue during rejection of the allografts examined. The rats were divided into four groups: group 1: Lewis rats (LEW) given a sham operation with dimethyl sulfoxide (DMSO); group 2: LEW given syngenic orthotopic liver transplantation (OLT) from LEW, with DMSO; group 3: LEW given allogenic OLT from ACI rats (ACI), with DMSO; and group 4: LEW given allogenic OLT from ACI, with ONO4057 as 10, 30, or 100 mg/kg per day dissolved in DMSO to subgroups 4a, 4b, and 4c, respectively. Histological examinations were performed, survival times monitored, and liver tissue PGE₂ levels 3, 5, 7, and 14 days after transplantation measured. The mean graft survival times in groups 4a, b, and c, at 37.5±10.4, 52.2±24.4, and 34.0±4.9 days (mean±SEM), respectively, were significantly longer than that in group 3 (at 13.0±3.2 days). Moreover, the levels of tissue PGE₂ in the liver allografts in group 4a were significantly higher than those in group 3 on days 5 and 7. These results suggest that ONO4057 has an immunosuppressive effect on liver allotransplantation since it reduces the activities of LTB₄ which augments immune responses, and also because it indirectly increases the PGE₂ level.