A class experiment in clinical pharmacology using beta-adrenoceptor antagonist drugs

Cardiac beta-adrenoceptor blocking activity was evaluated in a between-subject study carried out as a class experiment with pre-clinical medical students participating in a practical pharmacology course. From each of 10 groups of students, three healthy male volunteers, took oral propranolol 80 mg, pindolol 10 mg or placebo, according to a double-blind randomised protocol. Pre-treatment, and 45-60 min (1 h) and 105-120 min (2 h) post-treatment heart rate (HR) was determined electrocardiographically in the last 15 s during periods of rest (sitting for 5 min), isometric exercise (applying a standardized hand grip to a rolled sphygmomanometer cuff to elevate pressure from 50 to 150 mm Hg; 2 min) and dynamic exercise (bicycle ergometry with a load of 150 W for 3 min). Reductions from pre-treatment HR yielded statistically significant differences during exercise (isometric and dynamic) between all corresponding changes on placebo and active drugs (P less than 0.05-0.01), except with the 1 h post-propranolol hand grip HR. At rest, only the difference between 2 h HR changes on placebo and propranolol achieved statistical significance (P = 0.05); presumably, the partial agonist activity of pindolol overcame any minimal HR slowing liable to occur at rest. Cardiac beta-adrenoceptor blocking activity as judged by reductions in HR from pretreatment values, was more evident during cycling than during hand grip; and during hand grip than at rest.