The effect of intrinsic sympathomimetic activity of beta‐adrenoceptor blockers on circadian heart rate.

Abstract

1 The effect of a beta‐adrenoceptor blocker without intrinsic sympathomimetic activity (propranolol) and a beta‐adrenoceptor blocker with ISA (pindolol) on circadian heart rate was studied in 10 patients (3 women and 7 men) with an average age of 55 years and the following diagnoses: coronary heart disease (n = 7) and hypertension (n = 3). The therapy was carried out in a randomized, cross‐over study, with 3 × 40 mg propranolol and 3 × 5 mg pindolol. 2 Propranolol lowered the averaged circadian heart rate significantly (P less than 0.001) from 78 to 68 beats/min. The rate decreased both during the day and at night and the reduction was greater the higher the control value. The minimal hourly heart rate also decreased significantly (P less than 0.005) from 65 to 69 beats/min. 3 After pindolol the averaged circadian heart rate was not markedly changed. It reached a stable rate of around 70 beats/min. At a heart rate of below 70 beats/min an increase in rate was observed, whereas above 70 beats/min a reduction was found. The mean heart rate during the day remained unchanged. There was a significant relationship between the level of the control heart rate and the decrease in rate (r = 0.85, P less than 0.005). 4 In a bicycle exercise test of 1 Watt/kg body weight over a period of 6 min, both beta‐adrenoceptor blockers lowered blood pressure and heart rate to the same extent. 1982 The British Pharmacological Society