Effects of enalapril during continuous nitrate therapy: analysis of diameter of coronary arteries and platelet cyclic guanosine monophosphate

Is there a preferred antihypertensive therapy for isolated systolic hypertension and reduced arterial compliance?

Isolated systolic hypertension (ISH) is the most common type of hypertension and the most difficult type to control with antihypertensive therapy. ISH, by definition, is wide pulse pressure hypertension resulting largely from excessive large artery stiffness and representing an independent risk factor for cardiovascular disease in the older aged population. Two major intervention studies of ISH have shown significant benefit in reducing systolic blood pressure with active drug therapy, including thiazide diuretics and calcium receptor antagonists. The optimal treatment strategy is to maximize reduction in systolic blood pressure and to minimize reduction in diastolic blood pressure, thereby reducing pulse pressure. All classes of antihypertensive drugs reduce pulse pressure by means of lowering peripheral resistance, but certain drugs like nitrates, angiotensin converting enzyme inhibitors, and other drugs affecting the renin-angiotensin system have multiple actions that improve large artery stiffness and early wave reflection and are especially useful in treating ISH in the elderly.

Randomized, double-blind, placebo-controlled study of ascorbate on the preventive effect of nitrate tolerance in patients with congestive heart failure

BACKGROUND

Reduced cGMP production caused by increased superoxide has been proposed as a mechanism of nitrate tolerance during continuous nitrate therapy. This study was designed to evaluate the effects of ascorbate, an antioxidant, on the development of nitrate tolerance during continuous nitrate therapy in patients with congestive heart failure.

METHODS AND RESULTS

Twenty patients with congestive heart failure were randomized to receive intravenous infusion of nitroglycerin concomitantly with placebo (placebo group, n=10) or intravenous ascorbate (vitamin C group, n=10). After baseline measurements were obtained, dose titration was started by the infusion of nitroglycerin at a rate of 0.5 microg/kg per minute (titration period). Measurements of hemodynamic parameters and blood sampling were performed serially at 0, 6, 12, 18, and 24 hours after the titration period. At baseline, mean pulmonary artery pressure (MPAP, mm Hg), mean pulmonary capillary wedge pressure (PCWP, mm Hg), plasma vitamin E level (micromol/L), and platelet cGMP level (pmol/10[9] platelets) were comparable in the two groups (placebo group: MPAP, 48+/-6; PCWP, 24+/-4; cGMP, 0.76+/-0.12; vitamin E, 18.2+/-1.2; vitamin C: MPAP, 49+/-7; PCWP, 24+/-4; cGMP, 0.71+/-0.16; vitamin E, 18.6+/-1.3). In both groups, at 6 hours after the titration period, MPAP and PCWP were significantly decreased (placebo group: MPAP, 26+/-5; PCWP, 15+/-4; vitamin C: MPAP, 26+/-4; PCWP, 16+/-4), and platelet cGMP was significantly increased (placebo group: 2.42+/-0.24; vitamin C: 2.26+/-0.26). However, at 18 hours after titration, in the placebo group, MPAP (44+/-5) and PCWP (23+/-4) were increased, and platelet cGMP (0.85+/-0.20) and plasma vitamin E levels (12.4+/-1.4) were significantly decreased. In contrast, in the vitamin C group, MPAP (31+/-6), PCWP (17+/-5), platelet cGMP (2.49+/-0.23), and plasma vitamin E levels (17.6+/-1.4) were maintained for 18 hours after the titration period.

CONCLUSIONS

These findings indicate that ascorbate, an antioxidant, may prevent the development of nitrate tolerance during continuous nitrate therapy in patients with congestive heart failure.