Changes in myosin heavy chain and its localization in rat heart in association with hypobaric hypoxia-induced pulmonary hypertension.

Experimental pulmonary hypertension induced in a hypobaric hypoxic environment (HHE) is characterized by structural remodelling of the heart. In rat cardiac ventricles, pressure and volume overload are well known to be associated with changes in cardiac myosin heavy chain (MHC) isoforms. To study the effects of HHE on the MHC profile in the ventricles, 83 male Wistar rats were housed in a chamber at the equivalent of 5500 m altitude for 1-8 weeks. Pulmonary arterial pressure, right ventricular free wall (RVFW) weight, the ratio of RVFW weight over body weight (BW), the ratio of left ventricular free wall (LVFW) weight over BW, and myocyte diameter in both ventricles showed significant increases after 1 week, 2 weeks, 1 week, 6 weeks, and 4 weeks of HHE, respectively. Semi-quantitative reverse transcriptase-polymerase chain reaction revealed that beta-MHC mRNA expression was increased significantly in both ventricles at 6 and 8 weeks of HHE, whereas alpha-MHC mRNA expression was decreased significantly at 6 and 8 weeks of HHE in the right ventricle (RV) and at 6 weeks of HHE in the left ventricle (LV). The percentage of myosin containing the beta-MHC isoform was increased significantly at 4-8 weeks of HHE in RV and at 6 weeks of HHE in LV. In situ hybridization showed that the area of strong staining for beta-MHC mRNA was increased in both ventricles at 8 weeks of HHE, and showed a decrease from RVFW to cardiac septum, and from cardiac septum to LVFW. These results suggest that HHE has a significant effect on the expression of both MHC mRNA and protein in the heart, particularly in RV. These changes may reflect a role for cardiac MHC in the response to pulmonary hypertension in HHE. Copyright 2002 John Wiley & Sons, Ltd.