Felodipine, blood pressure, and cardiovascular reflexes in hypertensive humans.

The influence of acute and chronic treatment with felodipine on ambulatory intra-arterial blood pressure, certain cardiac reflexes, and plasma renin activity was studied in nine patients with essential hypertension. Acute oral administration of the drug caused a significant reduction in blood pressure associated with an increase in heart rate mediated by the sinoaortic baroreceptor-heart rate reflex. After 1 week of treatment reflex resetting had occurred, returning heart rate to normal despite continuing blood pressure reduction. This effect was maintained throughout 6 weeks of treatment. Withdrawal of treatment was followed by return of the blood pressure to control levels associated with significant bradycardia caused by reflex reactivation at its reset level. No change was observed in response to tilting or Valsalva's maneuver or in plasma renin activity. Ambulatory intra-arterial data suggested that the clinically useful antihypertensive action of felodipine persists for 9 hours.