Effects of labetalol and propranolol on responses to adrenaline infusion in healthy volunteers.

The effects of labetalol and propranolol were compared in eight healthy human volunteers using pulse rate and blood pressure changes in response to low rates of adrenaline infusion. Propranolol not only blocked but reversed the positive chronotropic and vasodepressor effects of adrenaline. Labetalol appeared to block these effects only partially. The alpha blocking property of labetalol may have contributed to this difference and hence is unlikely to cause alpha receptor mediated side-effects of endogenously released adrenaline in stress. This model is able to differentiate with great sensitivity between pure beta blockers and alpha beta blocking agents.