Acute and chronic rejection are frequent and significant complications of cardiac transplantation, and graft arteriosclerosis is the leading cause of death beyond the first year after transplant. Levels of endothelin-1 (ET-1) are elevated in plasma of patients with cardiac allografts and those with symptomatic vascular atherosclerosis, but little is known about the role of ET-1 in these processes. This study examined intragraft ET-1 expression in rat cardiac models of acute rejection and chronic rejection associated with graft arteriosclerosis. Corrected ET-1 gene transcript levels were measured with a [32P] dCTP reverse transcription polymerase chain reaction assay normalized with glyceraldehyde-3-phosphate dehydrogenase, and the gene product was evaluated by immunohistology with a monospecific anti-ET-1 antibody at different time points after transplant. ET-1 mRNA levels were significantly increased in acutely rejected (Wistar-Furth rat cardiac allografts transplanted into Lewis rat recipients) and chronically rejected (Lewis allografts transplanted into F344 recipients) vascularized cardiac allografts as compared with isograft controls. In acutely rejected allografts, peak expression occurred on day 5 after transplant. In chronically rejected allografts, the increase in ET-1 mRNA was sustained on days 7, 28, and 75. In both acutely and chronically rejected allografts, ET-1 mRNA upregulation was not seen in host spleens or paired host hearts. Immunohistological analysis confirmed that the bulk of ET-1 peptide expression was localized to mononuclear cells that diffusely infiltrated the graft interstitium (acute rejection and early chronic rejection) and accumulated within the neointima of chronically rejecting hearts with arteriosclerosis. These observations, taken together with in vitro data showing that ET-1 production is stimulated by certain cytokines, indicate that the allogeneic stimulus within rejecting vascularized cardiac allografts, presumably cytokine mediated, leads to significant intragraft up-regulation of ET-1 mRNA and peptide expression. The local up-regulation of this vasoactive and mitogenic peptide within acutely and chronically rejected cardiac allografts suggests that ET-1 may be involved in the development of graft arteriosclerosis.