[Changes of intermedin/adrenomedullin 2 and its receptors in the right ventricle of rats with chronic hypoxic pulmonary hypertension]

The purpose of the present study was to explore the expression changes of intermedin/adrenomedullin 2 (IMD/ADM2), a novel small molecular bioactive peptide, and its receptors, calcitonin receptor-like receptor (CRLR) and receptor activity modifying proteins (RAMP1, RAMP2, RAMP3) in the right ventricle of rats with chronic hypoxia-induced pulmonary hypertension. Twenty male Sprague-Dawley rats were randomly divided into 4-week hypoxia group and normal control group (each n=10). The rats in hypoxia group were placed in an isobaric hypoxic chamber, in which O(2) content was maintained at 9%-11% by delivering N(2), and CO(2) content was maintained at3% for 4 weeks (8 h/d, 6 d/week). The rats in the control group were housed in room air. The protein levels of IMD/ADM2 and adrenomedullin (ADM) in blood plasma and right ventricular tissue were measured by radioimmunoassay. The mRNA expressions of IMD/ADM2, ADM and their receptors CRLR, RAMP1, RAMP2, RAMP3 in right ventricular tissue were determined by reverse transcription-polymerase chain reaction (RT-PCR). The results showed that the ratio of right ventricle weight to left ventricle plus septum weight [RV/(LV+S)] and mean pulmonary arterial pressure (mPAP) were higher in hypoxia group than those in the control group (all P0.01), suggesting that the rat model of pulmonary hypertension was successfully established. However, the mean carotid arterial pressure (mCAP) between the two groups had no significant difference. Compared with that in the control group, ADM contents in plasma and right ventricular tissue in hypoxia group increased by 1.26 and 1.68 folds (all P0.01), respectively. Likewise, IMD/ADM2 contents in blood plasma and right ventricular tissue in hypoxia group increased by 0.90 and 1.19 folds (P0.01), respectively, compared with that in the control group. The data of RT-PCR showed that mRNA levels of ADM, IMD/ADM2 and RAMP2 in hypoxia group increased by 155.1% (P0.01), 80.9% (P0.01) and 52.9% (P0.05), respectively, compared with those in the control group. There were no significant differences in mRNA expressions of CRLR, RAMP1 and RAMP3 between the two groups (all P0.05). Taken together, the results show that the level of IMD/ADM2 increases in the rats with chronic hypoxia-induced pulmonary hypertension.