The Effects of a Cardioselective (Metoprolol) and a Nonselective (Propranolol) Beta‐adrenergic Blocker on the Response to Dynamic Exercise in Normal Men

We compared the effects of a cardioselective β-adrenergic blocking drug, metoprolol, with a nonselective β-adrenergic blocker, propranolol, on the response of 10 normal men to dynamic treadmill exercise. The volunteers underwent a standard graded' exercise test to exhaustion while receiving placebo; propranolol, 40 mg every 6 hours; propranolol, 80 mg every 6 hours; metoprolol, 50 mg every 6 hours; or metoprolol, 100 mg every 6 hours. The drugs were given in a double-blind fashion for 48 hours before exercise. Five days were allowed between successive drug administrations and the order of drug administration was randomized. Heart rate, arterial pressure, oxygen consumption, minute ventilation and CO2 production were monitored. Plasma drug concentrations were measured at the time of exercise. Judged'by plasma levels, propranolol was about three times more potent than metoprolol in attenuating heart rate. Both drugs produced a wide variation in plasma levels after a given oral dose, and both'drugs attenuated the systolic blood pressure response to exercise. Neither drug affected diastolic blood pressure or maximum oxygen consumption, maximum minute ventilation or the anae'robic threshold. We conclude that there is no evidence that the cardioselective drug metoprolol is superior to propranolol in terms of the ability to perform or respond to short-term maximal exercise. In addition, the fact that maximal oxygen consumption and the anaerobic threshold were unaffected implies that fatigue during exercise while on β-adrenergic blocking drugs is'not due to an effect of these drugs in limiting blood flow to the exercising extremities.