Long-Term Treatment With Imidapril but Not With Nifedipine Enhances Plasma NOx Concentration in Patients With Essential Hypertension

Abstract

We investigated whether long-term treatment with the angiotensin-converting enzyme (ACE) inhibitor imidapril or the calcium channel antagonist nifedipine increases systemic nitric oxide (NO) production in patients with essential hypertension. Twenty-nine patients with essential hypertension were randomly divided into two groups, and they were treated with either imidapril or nifedipine once daily p.o. for 4 weeks. Long-term treatment with imidapril significantly decreased blood pressure and increased plasma NOx concentration. Long-term treatment with nifedipine also caused a comparable extent of significant decrease in blood pressure, but failed to alter plasma NOx levels. The imidapril treatment significantly inhibited serum ACE activity and increased plasma bradykinin concentration. Furthermore, the extent of inhibition of serum ACE activity and the extent of increase in plasma bradykinin concentration in response to the imidapril treatment were both significantly correlated with the extent of increase in plasma NOx concentration. In contrast, no such changes were noted after the nifedipine treatment. These results provide the first evidence that long-term treatment with imidapril enhances plasma NOx concentration in patients with essential hypertension. This effect does not seem to be due to the decrease in blood pressure. The increase in bradykinin concentration may be involved in the enhancing effect of the ACE inhibitor on NOx production in vivo.