title: Analysis of the inotropic action of ouabain in rat ventricles: two apparent ouabain inotropic responses.
abstract: Two distinct inotropic effects of ouabain were observed in 68 of 82 right ventricular strips of rats with ED50s of 0.5 and 20 microM referred to as "low-dose" and "high-dose" effects, respectively. The other 14 strips showed monophasic dose-response curves, with an apparent ED50 of 0.3 microM; the inotropic response to ouabain or isoproterenol developed by these atypical strips did not exceed 50% over control. In the strips showing the biphasic inotropic response curves, the proportion of the "low-dose" effect varied from 6 to 89% of the maximum response. After treatment with 160 microM ouabain, followed by 60 min of washout, the maximum developed tension in response to ouabain was unchanged, but the "low-dose" effect was abolished or dramatically reduced. In those cases with a remaining "low-dose" response, the response was only 12% or less of the maximum and the ED50 was shifted from 0.3 to about 3 microM ouabain by the washout. The atypical strips, which showed only the "low-dose" effects during the first ouabain exposure, revealed after washout a consistent "high-dose" effect with an ED50 of about 12 microM ouabain. The data show that the two inotropic responses exist in all ventricular strips and that in some strips, after ouabain washout, a residue of the "low-dose" effect remains.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006352:Heart Ventricles / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D016276:Ventricular Function
chemical_list: D010042:Ouabain