In the present paper 32 genins and glycosides were tested for positive inotropic and arrhythmogenic activities at the isolated, spontaneously beating atrium of the guinea pig. It was found that: (a) substituents in C12-OHand C19-OH, respectively, diminished the efficacy 10-to 100-fold; (b) the acetylation at 16α-OH and 16β-OH, respectively, caused a 6- to 8-fold increase of efficacy, and (c) the esterification with acyl acids via hydroxyl groups at the sugar moiety caused a 2- to 10-fold decrease of efficacy depending on structure, number, and volume of the substituents. Similar results were gained with the cardioactive steroids at the (Na+-K+)-ATPase system and at the muscle tonus of the isolated guinea-pig ileum, demonstrating parallelism between these three parameters.
In the present paper 18 naturally occurring monosides and triosides and some semi-synthetic glycoside derivatives were investigated on their positive inotropic and arrhythmogenic properties in the isolated spontaneously beating guinea-pig heart. It could be shown that: (a) substitution of C19-OH causes a considerable decrease in efficacy; (b) acetylation of 16α-OH or 16β-OH leads to a 6–7-fold increase in efficacy; (c) esterification of hydroxy groups of the sugar moiety brings about only a slight decrease in efficacy regarding the range of inotropic effective concentrations, but decreases the maximal inotropic effect, and (d) that a dissociation between inotropic and arrhythmogenic effects is observed especially in the case of 16-acetyl·16-epi-gitoxin. The present findings are compared with former results obtained in the auricle preparation and with I50-values of the membrane ATPase system.
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