Exercise-induced increase in plasma arachidonic acid and thromboxane B2 in healthy men: effect of beta-adrenergic blockade

We examined the effects of beta-blockade with the nonselective antagonist propranolol, the cardioselective antagonist atenolol, and the cardioselective antagonist with partial agonist activity, practolol, on the levels of free arachidonic acid (AA), thromboxane B2 (TxB2), prostaglandin (PG) E2, and 6-keto-PGF1 alpha in plasma, and TxB2 production by platelets during clotting in six normal subjects during submaximal dynamic exercise. The drugs were given intravenously in equipotent increasing doses before the exercise test. Exercise induced a clear increase in AA, TxB2, and 6-keto-PGF1 alpha in plasma. During the first 60 min of exercise all three beta-blockers decreased the plasma levels of AA and TxB2. Propranolol (0.19 mg/kg) was slightly more effective than atenolol (0.19 mg/kg) or practolol (0.64 mg/kg); however, at exhaustion, propranolol was markedly more effective than the other two blockers. Plasma 6-keto-PGF1 alpha and PGE2 levels were less affected by beta-blockade during exercise, and no significant effect was seen on TxB2 formation by platelets. The plasma 6-keto-PGF1 alpha/TxB2 ratio was markedly higher after propranolol treatment than after treatment with the other two blockers during the exercise period. These results suggest that the capability of a nonselective blocker to inhibit both beta 1- and beta 2-adrenergic receptors may be of advantage because of the more effective inhibition of thromboxane formation than with a cardioselective blocker, especially when the sympathetic tone is markedly increased.