Abstract
The effect of addition of 4% bovine serum albumin to the perfusion medium on positive inotropic effects and on uptake of ouabain and digitoxin was studied in Langendorff preparations of guinea pigs. Albumin shifted the doseresponse curve of the positive inotropic effect, induced by digitoxin, to the right by a factor of about ten, while the ouabain-induced effects were not significantly altered. In addition, albumin strongly decreased the uptake of 3H-digitoxin by the Langendorff preparation, while it did not affect the uptake of 3H-ouabain. All effects observed can be related to the concentrations of a priori undbound glycosides. During the perfusion, apparently no measurable dissociation of the albumin-digitoxin complex took place. The relatively slow dissociation of this complex probably explains the slow onset of the digitoxin effect in vivo, compared with ouabain. Furthermore, it was calculated that the affinity of the digitoxin-receptor complex in the myocardium is much higher than the affinity of the digitoxin-albumin complex.
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