A study was made of the possible mechanisms underlying
bupicomide- and
hydralazine-induced increase of plasma
renin activity. Six patients with mild to moderate
hypertension were treated with both
bupicomide and
hydralazine on separate occasions in random order.
Bupicomide lowered mean arterial pressure from 124.2 +/- 3.7 mm Hg (mean +/- SE) to 107.2 +/- 3.9 mm Hg (P less than 0.001). The associated increase in plasma
renin activity was 1.27 ng/ml per hour and the increase in heart rate was 16.5 beats/min.
Hydralazine reduced mean arterial pressure from 124.2 +/- 3.7 mm Hg to 107.0 +/- 2.0 mm Hg (P less than 0.01). The associated increase in plasma
renin activity was 2.20 ng/ml per hour and the increase in heart rate was 22.4 beats/min. Plasma
renin activity during
bupicomide and
hydralazine administration correlated positively with control plasma
renin activity (r = 0.98, P less than 0.001). The log of plasma
renin activity correlated positively with heart rate (r = 0.51, P less than 0.02) and negatively with mean arterial pressure (r = -0.62, P less than 0.005). We conclude that control plasma
renin activity is a major determinant of change in plasma
renin activity during administration of
bupicomide or
hydralazine. Both an increase in sympathetic activity and a decrease in perfusion pressure may contribute to the
bupicomide- and
hydralazine-induced increase in plasma
renin activity, possibly by a baroreceptor-mediated increase in
adrenergic tone.