Influence of intravenous beta-adrenergic blockade with or without partial agonist activity upon plasma cyclic AMP and catecholamines in healthy subjects

In a randomised within-subject double-blind study, 7 healthy male volunteers, aged 32 to 40 years, received at rest intravenous infusions of 2 mg propranolol (devoid of partial agonist activity), 2 mg oxprenolol (with partial agonist activity) and placebo. Cuff blood pressure did not vary after any of the 3 treatments. The heart rate did not change after placebo, but fell in the first 5 min both after propranolol and oxprenolol (p less than 0.01); the rate was slightly lower after propranolol than oxprenolol (p less than 0.05). The heart rate remained lower after both beta-blockers than placebo from 5 to 60 min after the infusion (both p less than 0.01), but the difference between the two beta-blockers was no longer significant. Plasma cyclic AMP showed a peak rise at 2 and 3 min after oxprenolol, and remained unchanged at those times after propranolol and placebo. From the 5th to the 60th min after infusion, the cyclic AMP concentration was lower after both beta-blockers than placebo, and with a slightly but not significantly higher level on oxprenolol than propranolol. Plasma noradrenaline and adrenaline were higher after the beta-blockers compared to placebo. Oxprenolol evoked a smaller and non-significant rise in both catecholamines. That oxprenolol, unlike propranolol, causes a sudden rise in plasma cyclic AMP soon after an i.v. infusion may be due to its partial agonist activity.