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

Summary

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<0.01); the rate was slightly lower after propranolol than oxprenolol (p<0.05). The heart rate remained lower after both β-blockers than placebo from 5 to 60 min after the infusion (both p<0.01), but the difference between the two β-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 β-blockers than placebo, and with a slightly but not significantly higher level on oxprenolol than propranolol. Plasma noradrenaline and adrenaline were higher after the β-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.