Comparison of effects of enalapril and nitrendipine on cardiac sympathetic nervous system in essential hypertension

Objectives. The purpose of this study was to assess the effects of enalapril and nitrendipine on the cardiac sympathetic nervous system. Background. Angiotensin-converting enzyme inhibitors and long-acting calcium channel blockers have been widely used in the treatment of cardiovascular diseases, in some of which sympathetic overactivity plays major role in the pathophysiology and prognosis. However, little information is available on the effects of these drugs on the cardiac sympathetic nervous system. Methods. 123I-metaiodobenzylguanidine (MIBG) cardiac imaging was performed before and 3 months after drug administration in 46 patients with mild essential hypertension. Twenty-two patients were treated with 5 to 10 mg of enalapril once day, and the other 24 with 5 to 10 mg of nitrendipine once day. For comparison, 20 normotensive subjects were also studied. Results. There were no significant differences between the basal characteristics in the 2 hypertensive groups. In both hypertensive groups, both systolic and diastolic blood pressures were significantly reduced to similar levels after the 3-month drug treatment. Before the drug treatment, the 2 hypertensive groups had significantly higher washout rate and lower MIBG uptake than the normotensive subjects. The heart-to-mediastinum ratio significantly increased (p < 0.0001), with decreased (p < 0.002) washout rate after drug treatment in the enalapril group, but with no significant changes in the nitrendipine group. Conclusion. Enalapril could suppress cardiac sympathetic activity and nitrendipine had no effect on it. The knowledge of antihypertensive drugs on the cardiac sympathetic nervous system appears to be helpful in selecting appropriate treatment in cardiovascular diseases.