Abstract: Objective To investigate the effect of adrenomedullin (ADM) on hypoxic pulmonary vascular structural remodeling and proadrenomedullin N-terminal 20-peptide (PAMP) in rats with hypoxic pulmonary hypertension. Methods Twenty-four male Wistar rats were randomly divided into control group (n=8), hypoxia group (n=8) and hypoxia with ADM group (n=8). ADM was subcutaneously administered into rats of hypoxia with ADM group by mini-osmotic pump (300ng/h). The concentration of plasma PAMP was measured by radioimmunoassay, and the expression of PAMP in pulmonary artery was detected by immunohistochemical assay. Results Mean pulmonary arterial pressure, the ratio of right ventricular mass to left ventricular plus septal mass, and relative medial thickness and relative medial area of pulmonary arteries were significantly increased in hypoxic rats as compared with controls (P<0.01, respectively). Ultrastructural changes were also found in pulmonary arteries of hypoxic rats. Meanwhile, plasma PAMP concentration and the expression of PAMP by pulmonary arteries in hypoxic rats were markedly increased compared with controls. However, ADM obviously ameliorated above changes. Conclusion Intramolecular regulation of ADM may play an important role in the regulation of ADM on hypoxic pulmonary hypertension.