Abstract: BACKGROUND: The renin-angiotensin system plays a key role in the occurrence and development of hypertension, in which angiotensin (1-7) has antihypertensive effect and reversely regulates the adverse effects of angiotensin II. Exercise rehabilitation therapy is an important non-pharmaceutical means to prevent and treat hypertension; however, whether angiotensin (1-7) and exercise have a synergistic effect is not yet clear. 
OBJECTIVE: To explore the effect of angiotensin (1-7) supplementation combined with exercise therapy on cardiac remodeling in rats with renal hypertension and to investigate the possible mechanism of angiotensin (1-7) and its receptor signal axis. 
METHODS: Sixty male Sprague-Dawley rats were selected, of which 12 rats were randomly selected as normotensive group and the remaining 48 rats were used to make animal models of renal hypertension using two-kidney one-clip method and were then randomly divided into hypertension control group, hypertension exercise group, angiotensin (1-7) group and combined treatment group. One week after successful modeling, different interventions were given (for a period of 6 weeks) as follows: the hypertension exercise group was subjected to a running training on an electric treadmill, the angiotensin (1-7) group was perfused with angiotensin (1-7) by implanting Alzet microosmotic pump subcutaneously on the back of the rats, and the combined treatment group was perfused with angiotensin (1-7) after running training, while the normotensive group and hypertension control group were caged quietly. At 48 hours after the last training session, the tail artery blood pressure was measured with a non-invasive sphygmomanometer; the heart structure and function were detected by echocardiography; the left ventricular myocardium was taken for histopathological observation by hematoxylin-eosin and Masson staining, and the cardiomyocyte cross-sectional area and collagen volume fraction were obtained by image analysis software as markers of myocardial hypertrophy and fibrosis, respectively; the content of angiotensin (1-7) in the heart was detected by high performance liquid chromatography; the mRNA expression of cardiac embryonic genes, atrial natriuretic peptide and β-myosin heavy chain, was detected by real-time fluorescence quantitative PCR; and the protein expression of cardiac Mas receptor, angiotensin II type 2 receptor and endothelial nitric oxide synthase was measured by western blot assay. 
RESULTS AND CONCLUSION: Compared with the normotensive group, blood pressure increased (P < 0.05), cardiac function had no significant changes (P > 0.05), cardiomyocyte cross-sectional area and collagen volume fraction increased (P < 0.05), mRNA expression of atrial natriuretic peptide and β-myosin heavy chain was upregulated (P < 0.05), angiotensin (1-7) content and protein expression of Mas receptor, angiotensin II type 2 receptor and endothelial nitric oxide synthase was downregulated (P < 0.05) in the hypertension control group. Compared with the hypertension control group, blood pressure decreased (P < 0.05), cardiac function improved (P < 0.05), collagen volume fraction decreased (P < 0.05), cardiomyocyte cross-sectional area and angiotensin (1-7) content showed no significant changes (P > 0.05), mRNA expression of atrial natriuretic peptide and β-myosin heavy chain was downregulated (P < 0.05), and the protein expression of Mas receptor, angiotensin II type 2 receptor and endothelial nitric oxide synthase was upregulated (P < 0.05) in the hypertension exercise group; except for an increase in myocardial angiotensin (1-7) content (P < 0.05), other parameters had no statistical significance (P > 0.05) in the hypertension angiotensin (1-7) group. Compared with the hypertension exercise group, blood pressure decreased (P < 0.05), cardiomyocyte cross-sectional area and cardiac function had no significant changes (P > 0.05), collagen volume fraction decreased (P < 0.05), angiotensin (1-7) content increased (P < 0.05), mRNA expression of atrial natriuretic peptide and β-myosin heavy chain was downregulated (P < 0.05), and the protein expression of Mas receptor, angiotensin II type 2 receptor and endothelial nitric oxide synthase was upregulated (P < 0.05) in the combined treatment group. To conclude, supplementation of angiotensin (1-7) alone cannot improve cardiac remodeling in rats with renal hypertension, but it can enhance the efficacy of exercise. The mechanism is related to the improvement of angiotensin (1-7) receptor deficiency and restoration of its signaling pathway function.

Key words: renal hypertension, exercise, renin-angiotensin system, angiotensin (1-7), cardiac remodeling