Effect on heart rate over 24 hours of pindolol administered for 14 days.

The effect on heart rate of pindolol 5, 15 and 30 mg/day, a beta-adrenoreceptor blocker possessing intrinsic sympathomimetic activity, administered to 8 healthy volunteers for 14 days was studied. Heart rate was continuously recorded over 24 h during placebo treatment before each sequence, every 2 days during treatment, and then on the 15th, 17th and 18th days. Pindolol in the three doses used had no significant effect on mean heart rate over 24 h. It tended to lower mean diurnal heart rate non-significantly between noon and 6 p.m. Pindolol raised nocturnal heart rate between midnight and 6 a.m. to a comparable extent at all the doses used. Sympathetic tone is at its lowest during that period, which makes it possible to detect the intrinsic sympathomimetic activity of pindolol. After cessation of treatment, a rebound effect was observed, cardioacceleration being most marked after 30 mg/day.