Abstract
: The major limiting factor in long‐term administration of doxorubicin is the development of cumulative dose‐dependent cardiomyopathy and congestive heart failure. Although several mechanisms have been suggested to explain the exact cause of doxorubicin‐induced cardiomyopathy, the role of the vascular endothelium‐derived vasoactive mediators in the pathophysiology of this toxic effect is still unknown. Accordingly, the present study has been initiated to investigate whether the changes in plasma level of endothelin‐1 and nitric oxide along with cardiac nitric oxide are associated with the development of doxorubicin‐induced cardiomyopathy. Doxorubicin was injected with a single dose of 5 mg/kg and every other day with a dose of 5 mg/kg, intraperitoneally, to have four cumulative doses of, 10, 15, 20 and 25 mg/kg in five separate groups of male rats. An additional group receiving a single dose of 20 mg/kg and one receiving normal saline were also included in the study. Twenty‐four hr after the last dose, the animals were sacrificed and the plasma levels of endothelin‐1 and nitric oxide in addition to cardiac nitric oxide were determined. The results show that doxorubicin caused a statistically significant increase of 85%, 76% and 97% in plasma endothelin‐1 at a cumulative dose levels of 10, 15 and 20 mg/kg, respectively. However, the level of plasma nitric oxide remained unchanged. Furthermore, doxorubicin treatment resulted in a significant dose‐dependent increase in serum lactate dehydrogenase and creatine phosphokinase. In contrast, the increase in nitric oxide production in cardiac tissue by doxorubicin was not dose‐dependent with the maximum increase (81%) at a cumulative dose of 10 mg/kg. It is worth mentioning that plasma endothelin‐1 and cardiac nitric oxide were significantly increased at 24 hr after the single dose of 20 mg/kg doxorubicin. The increase of plasma endothelin‐1 and cardiac nitric oxide with the cardiomyopathy enzymatic indices, may point to the conclusion that both endothelin‐1 and cardiac nitric oxide are increased during the development of doxorubicin‐induced cardiomyopathy.