CGP 17/582B is a new beta-adrenoceptor antagonist which on experimental studies appears to combine selective beta 1-adrenoceptor blockade with partial agonist activity (ISA). Assessing beta-adrenoceptor selectivity and the degree of partial agonist activity in vivo can be difficult. 2. In a double-blind placebo controlled crossover study we have compared the effect of oral pretreatment for 7 days with CGP (100 mg twice daily), with propranolol (non-selective beta-adrenoceptor blocker with no ISA) and metoprolol (selective beta-adrenoceptor blocker with no ISA) on resting heart rate and heart rate response to submaximal exercise on a bicycle ergometer to assess the degree of beta-adrenoceptor blockade and also the changes in blood pressure, heart rate and potassium during the intravenous infusion of (-)-adrenaline to determine the degree of beta 2-adrenoceptor blockade. 3. Subjects underwent submaximal exercise testing on the second and fifth day of each treatment period and on the seventh day received a 2 h infusion of (-)-adrenaline (0.06 microgram kg-1 min-1). Heart rate, blood pressure, plasma potassium and catecholamines were measured throughout the study period. 4. All three active treatments significantly reduced exercise induced tachycardia. The (-)-adrenaline infusion significantly reduced plasma noradrenaline levels following propranolol and metoprolol and to a lesser extent with placebo but were unaltered on CGP. Baseline heart rate was unaltered by CGP but was significantly reduced by metoprolol and propranolol. Adrenaline significantly reduced plasma potassium levels following placebo and CGP pretreatment but plasma potassium was unaltered by adrenaline with metoprolol and propranolol pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)
