Effects of phenylpropanolamine and isometric exercise on blood pressure

The effects of a single dose of phenylpropanolamine (PPA) and isometric handgrip exercise were studied to determine whether the combination increases blood pressure more than either one alone. Six normotensive subjects performed 2 min of exercise at 30 percent of maximal effort before, 1 and 2 h after PPA 37.5 mg (immediate release formulation) or placebo. PPA alone increased the sitting systolic blood pressure at 2 h (PPA 7.2 +/- 8.2 mmHg, placebo - 1.8 +/- 3.4 mmHg, P = 0.016) but did not increase diastolic blood pressure. Handgrip exercise increased systolic and diastolic blood pressures to a similar extent 2 h after PPA (24.0 +/- 8.2/18.3 +/- 7.7 mmHg) or placebo (24.7 +/- 8.2/21.0 +/- mmHg). However, the total increase in systolic blood pressure after PPA + exercise at 2 h (increase in resting blood pressure + increase due to exercise, 31.2 +/- 8.9 mmHg) was greater than after placebo + exercise (22.8 +/- 9.3 mmHg, P = 0.048). These data suggest that the effects of PPA and handgrip exercise on blood pressure are additive. Because the contribution of PPA alone to the blood pressure increase was small and the dose of PPA used was greater than in most over-the-counter formulations, this interaction is probably of limited clinical importance.