The effect of intravenous dipyridamole on the cerebral and systemic circulations of the dog.

In 7 dogs anesthetized with halothane and nitrous oxide, dipyridamole was administered in a loading dose of 1 mg/kg supplemented with 0.5 mg/kg every 30 minutes. Cardiovascular parameters and organ blood flows (using the radioactive microsphere technique) were measured before and at 30 minute intervals after each administration of dipyridamole, for a total of 105 minutes. The administration of dipyridamole was associated with a 20% reduction in systemic arterial pressure, a 31% reduction in peripheral vascular resistance, and a 13% increase in cardiac index. Cerebrovascular resistance decreased 21%, but regional cerebral blood flow and metabolism were unchanged. Blood flow to the heart increased 355% in the right ventricle and 213% in the left ventricle. Blood flow to the jejunum decreased 52% while blood flow to the kidney and liver decreased slightly. The circulatory effects of dipyridamole are probably related to its interference with the inactivation of endogenous adenosine. The differential effects of dipyridamole on organ flow are similar to those seen following the IV infusion of adenosine.