RESUMEN
<p><b>OBJECTIVE</b>To observe the change of apelin and its receptor (APJ) in the lung tissue of rats with pulmonary hypertension induced by monocrotaline and to explore its significance.</p><p><b>METHODS</b>Twenty-five male SD rats were randomly divided into control group (n = 10) and monocrotaline group (n = 15). On the twenty-first day after the rats were intraperitoneally injected 60 mg/kg monocrotaline for monocrotaline group or equal volume vehicle for control group, the mean pulmonary artery pressure was measured by right heart catheterization. Histopathological study of lung tissue was done with hematoxylin-eosin (HE) and Masson's trichrome staining. The concentration of apelin in the plasma was measured by radioimmunoassay. The expressions of apelin/APJ proteins and genes in lung tissue were measured respectively by Western blot and reverse transcription polymerase chain reaction (RT-PCR).</p><p><b>RESULTS</b>The mean pulmonary arterial pressure, right ventricular hypertrophy, pulmonary vascular remodeling index, content of apelin protein in lung tissue of monocrotaline group were higher than those in control group. APJ protein and gene expression in monocrotaline group were significantly lower than those in control group (P < 0.01, P < 0.05), but apelin gene expression in the lung tissue between the two groups had no significant difference.</p><p><b>CONCLUSION</b>Endogenous apelin/APJ dysfunction may play an important role in the development of pulmonary hypertension induced by monocrotaline.</p>