Thirteen patients with
essential hypertension were treated with an alpha 1-adrenoceptor antagonist,
terazosin (1 to 4 mg/day) for 12 months. To assess the mechanism of its
antihypertensive effect, the hemodynamic and endocrinological responses to
terazosin were determined before, 3, and 12 months after the administration of
terazosin. Blood pressure significantly decreased within 2 weeks after the start of
terazosin and its effect was sustained throughout the 12 month period. Pulse rate did not change except slight increase in the third month. The hemodynamic studies revealed that total peripheral resistance significantly decreased and cardiac output slightly increased, indicating that the
antihypertensive effect of
terazosin is mainly produced by its vasodilation. Blood volume and plasma volume did not change. Although plasma
renin activity remained the same, plasma
aldosterone significantly decreased in response to
terazosin. Plasma
noradrenaline increased in the third month, but returned to the baseline level in the twelfth month. Thus,
terazosin monotherapy lowered blood pressure throughout one year without drug tolerance including volume expansion and/or accentuation of renin-angiotensin-aldosterone system or sympathetic function.