??-Blocking Potency of Mepindolol and Pindolol Against Isoproterenol-Induced Inotropic and Chronotropic Responses in Guinea Pig Atria

The beta-blocking potencies of mepindolol and pindolol were determined in guinea pig right atria (heart rate) and paced left atria (contractile force) in vitro. Neither agent showed selectivity for blocking rate responses induced by isoproterenol. The pA2 (95% confidence interval) values determined for mepindolol against rate and force responses induced by isoproterenol were 9.96 (9.91-10.01) and 9.52 (9.44-9.60), respectively, and for pindolol, 9.20 (9.15-9.25) and 8.85 (8.76-8.94). Mepindolol was approximately 6.5 times as potent as pindolol. The present evidence does not support the hypothesis of subpopulations of beta-receptors subserving inotropic and chronotropic responses.