THE EFFECT OF DIGITALIS ON THE ANESTHETIZED DOG I. ACTION ON THE SPLANCHNIC BED

¹ From the Cardiovascular Laboratory, Department of Physiology, Michael Reese Hospital, Chicago, Illinois

1. Acute experiments were carried out with therapeutic and toxic doses of digitalis (digifoline) given intravenously to determine the mode of its action. For this purpose, anesthetized dogs were used and the venous, arterial and portal pressures recorded simultaneously with the venous or portal flow measured with a modified Ludwig stromuhr. In some experiments, the liver was taken out of the circuit by shunting the portal blood past the liver directly into the jugular vein.

2. It was found that the experiments could be classed into two groups (a) those with arterial pressures above 80 mm. Hg and (b) those with arterial pressures below this level.

3. Digitalis in therapeutic doses causes a decrease in venous (and portal) flow in animals with high arterial pressure and an increase in flow in those with low arterial pressures. In both groups therapeutic doses of digitalis caused a rise in the arterial pressure, a fall in the venous pressure and a rise in the portal pressure.

4. When the liver was out of circulation, the action of the therapeutic doses of digitalis was less marked on the venous flow in animals with high arterial pressure, but similar in those with low arterial pressure. Its action on the arterial pressure was unchanged by this procedure, but the effect on venous pressure was more variable.

5. Toxic doses of digitalis caused a decrease in venous and portal flow in all animals, with a drop in arterial and portal pressures and at the same time a rise in venous pressure.

6. It is concluded from these results that the chief site of action of toxic doses of digitalis is directly on the heart.

7. It is concluded from these results that the chief, if not the sole, site of action of therapeutic doses of digitalis is on the peripheral vessels, in particular those of the liver including the hepatic vein sphincter. In the animals with low arterial pressure the digitalis in therapeutic doses in addition to the action on liver vessels acted on the heart indirectly due to improvement of the coronary flow by virtue of its pressor effect on the arterial blood pressure.

8. The bearing of these observations to the mode of action of digitalis in man is discussed. An attempt is made to account for the apparent contradictions in results reported in the literature.

9. The experiments reported emphasize the important rôle played by the liver vessels in regulating blood flow, circulating blood volume and heart action. The liver vessels which are the portal of exit of the splanchnic vascular blood play a significant rôle in the redistribution of blood in the body.

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