Abstract
The antagonistic potency, pA2, of several non-selective β-antagonists on presynaptic β-adrenoceptors was evaluated using a parallel line assay and MacKay's equation against isoproterenol-induced increases in 3H release in isolated guinea-pig pulmonary arteries preloaded with 3H-norepinephrine. Cumulatively applied isoproterenol at 10-9 M, 10-8 M and 10-7 M dose-dependently increased 3H release evoked by transmural field stimulation at 1 Hz. β-Antagonists tested dose-dependently antagonized the isoproterenol-induced increases. The order of pA2 was carteolol (11.23±0.09)>nadolol (9.78±0.05)>pindolol (9.59±0.03)>propranolol (9.26±0.17). Carteolol has the highest pA2 and is a useful tool for clarifying whether or not presynaptic β-adrenoceptors tonically function.
