EL-SAYED, M. S. Extrinsic plasminogen activator response to exercise after a single dose of propranolol.Med. Sci. Sports Exerc., Vol. 24, No. 3, pp. 327–332, 1992. The level of plasminogen activators was measured in 12 volunteers at rest and after maximum exercise. Two formulations of a beta-blocker “propranolol,” or placebo, were given (oral dose, 10 mg) 2 h before exercise commenced. At weekly intervals over 21 d, randomized double-blind, cross-over trials were conducted. Two hours after drug/placebo administration, subjects exercised to maximal capacity using an incremental exercise protocol on a bicycle ergometer. Before and 2 h after drug/placebo administration and immediately after maximum exercise, heart rate, blood pressure, and oxygen consumption were measured, venous blood was removed, and plasma separated for the measurement of plasminogen activators using the fibrin plate method. Duplicate portions of plasma were taken: portion 1 for determination of total plasminogen activators activity, by the addition of dextran sulphate and flufenamic acid; portion 2 to assay extrinsic plasminogen activator, intrinsic plasminogen activator being blocked by the addition of C1-inactivator. Resting and postmaximum exercise heart rates showed significant decreases (P< 0.05), with a nonsignificant difference in the resting level of extrinsic and intrinsic activators when the subjects were premedicated with either of the two formulations. Total and extrinsic activities, but not intrinsic activity, were significantly increased (P< 0.05) to maximum exercise when subjects were given placebo. However, premedication with the drug formulations 1 and 2 significantly decreased (P< 0.05) the normal total and extrinsic activities response to maximum exercise, with no effect on the intrinsic activity. It is suggested that the resting level of activators activity may not be affected by premedication with propranolol. After maximum exercise without medication (placebo), there was an increase in total plasminogen activator mainly due to an increase in extrinsic plasminogen activator, but with medication only extrinsic plasminogen activator response was decreased, and therefore this response may be beta-adrenergically mediated.