Long-term converting enzyme inhibition and sympathetic nerve function in hypertensive humans

Orthostatic hypotension is uncommon during oral converting enzyme inhibition, even when combined with salt depletion. To assess the mechanisms responsible for the cardiovascular homeostasis in this condition, we studied the blood pressure (BP), heart rate (HR), total plasma catecholamines (CA), and plasma renin activity (PRA) responses after 20 minutes of 60 degrees head-up tilt in four groups of hypertensive patients. Group 1 included seven untreated patients; Group 2, eight patients on converting enzyme inhibitor (captopril) therapy; Group 3, six patients on diuretic therapy and Group 4, 15 patients on combined captopril and diuretic therapy. Long-term converting enzyme inhibition alone or in combination with diuretics resulted in reduction of mean arterial pressure (MAP) associated with a marked increase in PRA and fall in plasma aldosterone concentration (PAC). Pronounced increases in HR and plasma CA on tilt were observed in all groups. In Groups 1, 2, and 3, BP was maintained during tilt; in Group 4, three patients fainted between 5 and 15 minutes while the other 12 had a normal response to tilt. Plasma catecholamines increased more significantly after 15 and 20 minutes of tilt, more in Groups 3 and 4 than in Group 1, while no differences in HR response were observed among groups. Results suggest that sympathetic compensatory mechanisms are adequate in the majority of patients to maintain BP during converting enzyme inhibition even when combined with salt depletion. In a few who exhibited orthostatic hypotension, a vasovagal attack seemed to be responsible for bradycardia and fall in BP.