Effect of cardiac glycosides on blood volume of the dog

¹ Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia

The effects of cardiac glycosides on plasma volume, extracellular water volume, hematocrit reading, concentrations of hemoglobin and plasma proteins, and calculated blood volume were determined in both conscious and anesthetized dogs. The administration of 40% of the fatal dose of a cardiac glycoside had no statistically significant effects upon any of the parameters measured which could be ascribed to direct vascular actions of the drug. Thus, the plasma and extracellular water volumes were generally unaffected by either the injection of a cardiac glycoside or its solvent. In several experiments with conscious dogs, however, plasma volume decreased after injection of a glycoside apparently due to the development of severe vomiting. Hematocrit readings and hemoglobin concentrations were frequently moderately elevated after injection of a glycoside in normal dogs. The latter changes were apparently due to glycoside-induced splenic contraction, since they were absent in splenectomized dogs. It is concluded that the decrease in cardiac output caused by cardiac glycosides in normal dogs is not the result of a decrease in blood volume.