The effect of phenylpropanolamine on blood pressure during upright bicycle exercise in normal subjects

We studied the effect of a single oral dose (37.5 mg immediate release) of phenylpropanolamine (PPA) in six normal subjects during upright incremental bicycle exercise to symptom tolerance. The study was double blind and placebo controlled with a crossover design. The patients rested supine for 90 minutes after dosing, sat quietly on the bicycle for five minutes, and then began exercise. After PPA systolic blood pressure was increased during supine rest (135 ± 14 mmHg vs 120 ± 10 mmHg for placebo; P < 0.01) and while sitting on the bicycle prior to exercise (131 ± 8 mmHg vs 121 ± 8 mmHg for placebo; P < 0.05). However, PPA did not alter the expected increase in systolic blood pressure with progressive exercise. Systolic blood pressure at maximum exercise (254 ± 43 watts) was 185 ± 14 mmHg for PPA vs 182 ± 13 mmHg for placebo (difference not significant). This suggests that the physiological factors controlling blood pressure during exercise (increased cardiac output, vasodilation of vessels in exercising muscles and vasoconstriction of non-exercising vascular beds) are not altered significantly by a dose of PPA sufficient to increase resting systolic blood pressure, at least in normal subjects.