Aim To investigate the dynamic changes of adrenomedullin mRNA expression and its level in the hypothalamus of stress-induced-hypertensive rats. Methods 58 male SD rats were divided into control group(n=23) and stress group(n=35) receiving noise or noise with electric foot shock randomly combined and output by a computer for 15 days.48 rats were executed and their hypothalamus were separated to monogenate individually at stress 1,5,10 and 15 days and post-stress 5 and 10 days(for each subgroup n=3 or n=5).The changes of the adrenomedullin mRNA expression were determined by reverse transcription-polymerase chain reaction method. The levels of adrenomedullin were examined by radioimmunoassay.Another 10 rats were divided into the control group(n=5) and the stress group receiving stress for 10 days to detect the immunoreactive changes in hypothalamus with immunohistochemistry method. Results After stress for 5 days,the artery pressure significantly increased and reached a peak on 15th day(156.3±3.3 mmHg vs 114.0±2.6 mmHg,P<0.01).The artery pressure significantly increased.Even post-stress for 10 days,the artery pressure still kept at high level.Compared with the control group at each time point,ADM mRNA expression in the hypothalamus up-regulated within 10 days(day 5,0.99±0.05 vs 0.92±0.04,P<0.05;day 10,1.26±0.04 vs 0.92±0.04,P<0.01),and then downregulated,but still kept at a high level at 15 days (1.00±0.04 vs 0.92±0.04, P<0.05).ADM levels increased within 10 days compared with control group(day 1,1.25±0.22 vs 0.93±0.19,P<0.05;day 5,1.69±0.29 vs 0.97±0.21,P<0.01;day 10,2.00±0.28 0.94±0.24,P<0.01),then decreased to the levels of the control group. With immunohistochemistry method,detected adrenomedullin immunoreactive neurons significantly strengthened in the paraventricular neucleus of the hypothalamus in the stress group compared with the control group(110.21±3.10 vs 127.56±3.50,P<0.01). Conclusion The results suggested that footshock and noise stress for a longer time induced a significant increase in blood pressure,while adrenomedullin mRNA and levels significantly increased in hypothalamus,especially in the paraventricular neucleus of the hypothalamus,indicating that ADM in the hypothalamus might involve in the pathophysiological process of the development of stress-induced hypertension.