title: The influence of polar and non-polar digoxin and digitoxin metabolites on the 86Rb-uptake of human erythrocytes and the contractility of guinea pig papillary muscles.
abstract: The potency of various digoxigenin and digitoxigenin derivatives with different polarity was tested in two biological systems: First, in an 86-Rb-erythrocyte assay which allows to determine the influence on active cation transport (measured as the glycoside concentration exerting half maximal inhibition of 86-Rb-uptake of human erythrocytes = IC50). Second, with isolated guinea pig papillary muscle, which allows to determine glycoside effects on contractile force (measured as the glycoside concentration exerting 100% increase of contractile force = C+100%). The IC50 of the substances covered a range from 3.2 to 4800 X 10(-9) M, the C+100% from 0.7 to 978 X 10(-6) M. In both assay systems the glucuronides of glycosides and genins were between 1.4 and 11 times less potent than the original substances. A highly significant correlation (p less then 0.0001) was found between IC50 and C+100% (r = 0.9996) and between log IC50 and log C+100% (r = 0.9819), the slope for the latter correlation being nearly unite (= 0.9912). The results support the hypothesis that inhibition of active cation transport is and important step in glycoside incuced posite-inotropic effect.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D004074:Digitoxin / Q000031:analogs & derivatives* / Q000494:pharmacology; D004077:Digoxin / Q000031:analogs & derivatives* / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D005965:Glucuronates / Q000494:pharmacology; D006168:Guinea Pigs; D006801:Humans; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D012413:Rubidium / Q000097:blood*; D013329:Structure-Activity Relationship; D013431:Sulfates / Q000494:pharmacology
chemical_list: D005965:Glucuronates; D013431:Sulfates; D004077:Digoxin; D004074:Digitoxin; D012413:Rubidium