Nifedipine, a
calcium channel blocker exerts significant peripheral vasodilatory activity in hypertensive
patients. It has been postulated that the
antihypertensive effect of peripherally acting
vasodilators is masked, by counter regulatory mechanism e.g. activation of
renin-
angiotensin aldosterone (RAA) axis. The present
work was undertaken to study the effect of blockade of RAA axis using
captopril, an
angiotensin converting enzyme inhibitor on the
blood pressure lowering activity of
nifedipine. Pretreatment with
captopril in a
dose of 25 mg. bd was carried out for 4 weeks in one group of 10
patients before administering
nifedipine 10 mg bd for 4 weeks. The other
matched group of 10
patients received
nifedipine alone in the same
dose. It was observed that although
captopril by itself had no appreciable effect on
blood pressure in the
dose used, it significantly enhanced the
blood pressure lowering activity of
nifedipine. It appears that counterregulatory mechanisms
play an important
role in determining the net
antihypertensive effect of peripheral
vasodilators.