A trial for kinetic evaluation of the antagonistic potency of several beta-antagonists on presynaptic beta-adrenoceptors.

The antagonistic potency, pA2, of several non-selective beta-antagonists on presynaptic beta-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. beta-Antagonists tested dose-dependently antagonized the isoproterenol-induced increases. The order of pA2 was carteolol (11.23 +/- 0.09) greater than nadolol (9.78 +/- 0.05) greater than pindolol (9.59 +/- 0.03) greater than propranolol (9.26 +/- 0.17). Carteolol has the highest pA2 and is a useful tool for clarifying whether or not presynaptic beta-adrenoceptors tonically function.