Participation of the renin system in treatment-resistant hypertension as measured by acute blockade of the angiotensin converting enzyme.

The acute blood pressure response to the angiotensin converting enzyme inhibitor, captopril, was used to measure participation of the renin-angiotensin system in treatment-resistant hypertension. By 2 h after a single 25-mg oral captopril dose in patients still receiving a diuretic-vasodilator-beta-blocker combination, systolic and diastolic blood pressures had fallen significantly; the decrease in diastolic pressure correlated with the control (immediately pre-captopril) plasma renin activity (r = 0.64, p less than 0.001). Apart from its possible contribution to the underlying hypertension, this captopril-identified renin component may have reflected diuretic and vasodilator-induced renin stimulation that could not adequately be prevented by the renin-lowering properties of the beta-blocker. Captopril, and perhaps other specific antirenin drugs, therefore, may be valuable adjuncts to treatment in patients with hypertension refractory to conventional therapy.