Captopril, alone and in combination with hydrochlorothiazide, on responses to upright tilt in conscious dogs.

Orthostatic hypotension occurs relatively frequently in antihypertensive therapy. Although vasodilators are usually not associated with this response, hydralazine and to some extent minoxidil produced marked orthostasis in conscious dogs in a prior series of experiments. Captopril also reduces blood pressure by a peripheral mechanism. Therefore, its influence on responses to upright tilt were evaluated. Oral administration of captopril reduced blood pressure of conscious normotensive dogs. Even greater falls occurred after pretreatment with hydrochlorothiazide. However, the increases in blood pressure and heart rate observed during upright tilting were not altered by captopril.