Increased endothelin expression in a rat cardiac allograft model of chronic vascular rejection

Endothelins (ET) are potent vasoconstrictors that are directly mitogenic for vascular smooth muscle cells and fibroblasts. It is possible that the vasoconstrictor and mitogenic effects of ET could play a significant role in the vascular remodeling process that occurs in chronic vascular rejection (CVR). We have previously shown that cardiac allografts in the indefinitely surviving major histocompatibility complex identical WF.1L (RT1(1)) to Lewis (LEW) (RT1(1)) inbred rat strain combination provide a highly reproducible model of progressive CVR. The objective of this investigation was to measure endothelin-1 ventricular content of WF.1L-LEW cardiac allografts and to determine the immunohistochemical patterns of ET cellular reactivity at well defined posttransplant time periods. Data were compared with those obtained in similar studies of LEW-LEW syngeneic: heart grafts as well as all recipients' own hearts. The ventricular ET-1 content of the WF.1L cardiac allografts was markedly higher (4.3-, 7.0-, and 4.8-fold at 20, 40, and 60 days, respectively) than in corresponding recipients' hearts. Also, the increase in ventricular ET-1 levels as compared with the recipients' hearts rose significantly only in the allograft group. No comparable differences were observed in the syngeneic heart graft controls. Allografts consistently showed ET staining of intimal myocytes at sites of occlusive and subocclusive intimal proliferation associated with CVR. Allografts also showed ET cellular staining in areas of reparative fibrosis associated with indolent interstitial rejection and ischemic myocardial damage. The results of this study strongly suggest that ET may play a significant role in the pathogenesis of CVR.