FURTHER OBSERVATIONS ON THE CIRCULATORY ACTIONS OF DIGITALIS AND STROPHANTHUS WITH SPECIAL REFERENCE TO THE LIVER, AND COMPARISONS WITH HISTAMINE AND EPINEPHRINE

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Abstract
Experi-ments on 11 dogs are reported. The observations are: When dogs are given, by intravenous injection, doses of digitalis corresponding to the full therapeutic dose for man, they exhibit a rise in arterial and fall in right auricular pressure, but a simultaneous rise in portal vein pressure. These changes are also caused by strophanthus. The fall in systemic and rise in portal vein pressure are due to constriction of hepatic veins. This agrees with the hepatic engorgement in digitalized dogs, which was previously reported, and also with the effects of digitalis on excised veins and in liver perfusion ex- periments which other observers have reported. After eliminating the liver from the circulation by shunting the portal blood directly into the inferior vena cava, or by ligating the arteries which supply the splanchnic area, digitalis or strophanthus did not cause a fall of venous pressure, but in several instances raised it, and did not cause as marked an elevation of arterial pressure as in the animals with the splanchnic circulation intact. Therefore the fall in right auricular pressure, after giving digitalis to dogs with the hepatic circulation intact, was due to diminished venous return flow, and ultimately to an accumulation of blood in the splanchnic or portal region as a result of obstructed hepatic outflow (hepatic vein constriction). This mechanism adequately explains the diminution in cardiac output after digitalis, since a diminished venous return must result in deficient cardiac filling. This conclusion agrees with that of the authors'' previous paper. The experimental procedures used to determine the actions of digitalis and strophanthus were controlled by comparisons in the same organism with known actions of histamine and epinephrine which cause a similar pooling of portal blood through a similar mechanism, the actions being modified, however, by changes in other vessels.

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