MYOCARDIAL UPTAKE OF DIGOXIN IN CHRONICALLY DIGITALIZED DOGS

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Abstract
The time course of myocardial uptake of digoxin, increase in contractility and changes in myocardial potassium concentration was studied for 90 min following an intravenous digoxin dose to long‐term digitalized dogs. Nineteen dogs were investigated by the use of a biopsy technique which allowed sampling before and after administration of digoxin. Ten minutes after administration of digoxin the myocardial concentration increased from 60 to 306 nmol/kg tissue; the myocardial concentration of digoxin was significantly lower (250 nmol/kg tissue) after 30 min and then increased again. The transmural myocardial distribution of digoxin was uniform before and 90 min after administration of digoxin in long‐term digitalized dogs but at 10 min after administration, both the subepicardial and the subendocardial concentration of digoxin were significantly lower than that of the mesocardial layer. During the first 10 min the dp/dtmax increased to 135% of the control level. The increase remained unchanged during the rest of the study. Myocardial potassium decreased throughout the study. The M‐configuration of the myocardial uptake curve and the non‐uniformity of myocardial distribution of digoxin observed at 10 min after administrating digoxin to long‐term digitalized dogs indicate that the distribution of myocardial blood flow may be changed during chronic digitalization.