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.