The influence of antihypertensive therapy on the structural arteriolar changes in essential hypertension: different effects of enalapril and hydrochlorothiazide.

OBJECTIVES

To assess the peripheral and central haemodynamics, in particular the effect on minimal resistance in the hand, with an ACE inhibitor in comparison with a diuretic.

DESIGN

Double-blind randomized parallel group study.

SUBJECTS

Twenty-eight previously untreated men with essential hypertension (supine diastolic blood pressure > 95 mmHg repeatedly on placebo). METHODS/INTERVENTION: Causal and intra-arterial blood pressure, dye-dilution technique, water plethysmography at rest and at ischaemia, enalapril (n = 14), hydrochlorothiazide (n = 14).

RESULTS

After 6 months the mean arterial pressure was reduced from 112.7 to 96.9 mmHg (change -15.9 mmHg; 95% confidence interval (CI) -21.9, -9.8) on enalapril and from 110.1 to 101.5 mmHg (change -8.6 mmHg; CI -14.4, -2.8). Heart rate did not change on any of the therapies. Enalapril reduced blood pressure mainly through a reduction in total peripheral resistance (delta -3.0 PRU100; CI -5.6, -0.4) while hydrochlorothiazide reduced blood pressure mainly through a reduction in cardiac output (delta -0.8 l/min-1; CI -1.5, -0.07). Minimal vascular resistance (mean of right and left hand) displayed a significant time x treatment interaction indicating a different trend with enalapril than hydrochlorothiazide with a change of -0.12 PRU100 (CI -0.33, 0.05) on enalapril and a change of 0.14 (CI -0.29, 0.56) on hydrochlorothiazide. The resistance level after 6 months was significantly higher on hydrochlorothiazide than on enalapril (P = 0.0105).

CONCLUSION

Enalapril reduced blood pressure through vasodilatation and hydrochlorothiazide through decreased cardiac output. The two therapies also affected minimal vascular resistance (an indirect measure of vascular wall thickness) differently; with enalapril showing a favourable response in contrast to hydrochlorothiazide.