Enalapril Acts Through Release of Nitric Oxide in Patients With Essential Hypertension*

BACKGROUND: Endothelial dysfunction has been proposed as an etiological agent in the pathogenesis of essential hypertension. Amongst the various antihypertensive drugs, angiotensin converting enzyme inhibitors (ACEI) have been implicated in modifying the vascular endothelium by the release of mediators that include bradykinin, nitric oxide, prostaglandins and thromboxane A2. MATERIALS AND METHODS: To study the mechanism of action of enalapril, an ACEI, serum reactive nitrite intermediates (RNI) and citrulline, by products of nitric oxide metabolism were measured before and after treatment with enalapril in 25 consecutive patients of essential hypertension. RESULTS: Following treatment serum RNI intermediate increased from a pretreatment value of 164.5 +/- 20.2 nmol/mL to a post treatment value of 266.9 +/- 47.3 nmol/mL (p < 0.05), however there was no significant change in the levels of citrulline (p > 0.1). There was no significant correlation between the severity of hypertension and serum RNI. Serum RNI levels were lower in the postmenopausal women but did not reach statistical significance. CONCLUSIONS: It is postulated that enalapril exhibits its antihypertensive property through release of nitric oxide.