AIM: The aim of this study is to investigate the acute inhibitory effects of adrenomedullin(ADM 1-52 ) on hypoxia pulmonary hypertension and its influence on systemic blood pressure. METHODS: Thirty-six male Wistar rats were divided into two groups. Eighteen were exposed to hypoxia for 21 days as hypoxic pulmonary hypertension group,and another eighteen were kept in ambient as control group. Each group were divided into three subgroups which were injected intravenously with ADM 0 1 nmol/kg, 0 3 nmol/kg, 1 nmol/kg, respectively,then hemodynamic parameters were recorded. Plasma cyclic adenosine 3,5,-monophosphate (cAMP) was measured by radioimmunoassay before,during and after injection of 0.3nmol/kg adrenomedullin(ADM 1-52 ). RESULTS: Mean pulmonary arterial pressure (mPAP)in the hypoxia and control rats treated with ADM decreased, the fall in hypoxia rats is more obviously than control( P