Abstract: Objective To investigate the cardiac expression of angiotensin-converting enzyme(ACE) and ACE2 in spontaneously hypertensive rats (SHR) and the effects of enalapril on them, and to thereby explore the role played by ACE and ACE2. Methods Fifteen SHR were randomly assigned to two groups: SHR control group（n=7）which were treated with vehicle and enalapril group（n=8）which were treated with enalapril (15mg.kg-1.d-1).The treatment lasted for 4 weeks. After the treatment, the rats were killed and the left ventricle was dissected carefully. Reverse transcription polymerase chain reaction(RT-PCR) and western blot protein staining were performed to detect the expression of mRNA and protein of ACE and ACE2 respectivlely. Ten WKY rats surved as the normotensive control group which were also treated with vehicle.Results In SHR, when compared with the normotensive WKY, the cardiac expression of both mRNA and protein of ACE in SHR was obviously increased(1.68±0.34 vs 0.33±0.12, P<0.05;1.21±0.14 vs 0.71±0.11, P<0.05), whereas the cardiac levels of both mRNA and protein of ACE2 were significantly decreaed(0.50±0.15 vs 1.16±0.24, P<0.05; 0.71±0.24 vs 1.22±0.14, P<0.05). After treatment with enalapril,the expression of both ACE mRNA and ACE protein was obviously decreased(0.44±0.19 vs 1.68±0.34, P<0.01; 0.87±0.13 vs 1.21±0.14, P<0.05) and the expression of ACE2 mRNA significantly elevated (1.77±0.49 vs 0.50±0.15,P<0.05), but ACE2 protein remained unchanged (0.42±0.22 vs 0.71±0.24, P>0.05).Conclusion In SHR, the expression of cardiac ACE was remarkably increased, whereas ACE2 was notably decreased.These changes might contribute to the initiation and progression of hypertension in SHR. Enalapril could markedly reduce the expression of ACE and elevate the level of ACE2, and these effects on ACE and ACE2 might play parts in the antihypertensive function of angiotensin converting enzyme inhibitors(ACEI).

Key words: Spontaneously hypertensive rat, Wistar kyoto rat, Angiotensin- converting enzyme, Angiotensin-converting enzyme 2, Enalapril