Myocardiopathy and expression of atrial natriuretic peptide in rats with monocrotaline-induced pulmonary hypertension.

Myocardiopathy in rats with monocrotaline (MCT)-induced pulmonary hypertension was investigated morphologically and immunohistochemically. A single subcutaneous injection of MCT (60 mg/kg body weight) to SD rats produced progressive cardiac lesions. Histologically, the lesions were characterized by myocardial hypertrophy and myocardial degeneration followed by mononuclear cell infiltration and fibroblast proliferation in the right atrium and ventricle. Such histological changes began to be seen 3 weeks after injection and thereafter progressively developed in rats killed 4 and 5 weeks after injection. These findings indicate progressive hypertrophic myocardiopathy, due probably to pulmonary hypertension induced by MCT. Immunohistochemically, atrial natriuretic peptide (ANP)-positive myocardial cells were frequently observed in the left and right ventricle in MCT-treated rats killed 4 and 5 weeks after injection. The intensive immunopositive reaction was observed mainly in hypertrophic myocardial cells in the subendocardium of the right ventricle and also present in hypertrophic myocardial cells around injured areas consisting of degenerated myocardial cells, mononuclear cell infiltration and fibrosis. These findings suggest a close relationship between the ANP expression and cardiac hypertrophy in MCT-treated rats.