ACTIVE AND PASSIVE EFFECTS OF ANTIHYPERTENSIVE DRUGS ON LARGE ARTERY DIAMETER AND ELASTICITY IN HUMAN ESSENTIAL-HYPERTENSION

The effects of antihypertensive drugs on the large arteries consist of two parts: the passive effect due to the change in pressure and the active effect, the drug action per se. This study proposes a method of dissociating the passive effect from the active effect. The diameter of the arterial artery was determined by the pulsed Doppler method and the pulse wave velocity of the brachioradial artery by mecanography. Arterial compliance was calculated by the Bramwell-Hill formula. Active and passive effects were determined by a logarithmic pressure-diameter model. This model was supported by in situ direct measurements of blood pressure and diameter in a segment of the femoral artery in dogs. Six drugs, cadralazine, ketanserin, medroxalol, nitrendipine, captopril, and isosorbide dinitrate, administered orally, were tested in 70 essential hypertensive patients. For all drugs, the pressure reduction induced a passive decrease in arterial diameter (p < 0.02 to p < 0.01). Cadralazine actively decreased arterial diameter (p < 0.01), ketanserin had no active effect on diameter, and medroxalol, nitrendipine, captopril, and isosorbide dinitrate actively increased arterial diameter (p < 0.05, p < 0.01, p < 0.01, and p < 0.01, respectively). For all drugs, the pressure reduction also induced a passive increase in arterial compliance (p < 0.05 to p < 0.01). However, only nitrendipine, captopril, and isosorbide dinitrate actively increased arterial compliance (p < 0.01, p < 0.05, and p < 0.01, respectively). Under nitrendipine, captopril, and isosorbide dinitrate, the pressure-induced increases in arterial compliance were 16, 11, and 14% of pretreatment values, while the active increases were 37, 49, and 50% of pretreatment values. Thus not all antihypertensive drugs have an intrinsic effect on arterial diameter and compliance. However, when they exist, these active effects may strongly potentiate the passive effects.