EFFECTS OF DIPYRIDAMOLE AND ADENOSINE INFUSIONS ON OVINE PULMONARY AND SYSTEMIC CIRCULATIONS

This study was designed to test the hypothesis that A(2) adenosine rec eptors mediate the hemodynamic responses to intravenous infusions of d ipyridamole. We tested the hypothesis using theophylline, which has be en reported to block A(2) adenosine receptors and thereby attenuate th e vasodilation caused by adenosine. Twenty-four anesthetized lambs tha t were between 7 and 17 days of age were used. Basal vascular tone of each animal was increased with the thromboxane mimetic U-46619. A theo phylline dose commonly used in humans (5.0 mg/kg infused over 30 min f ollowed by 1.0 mg . kg(-1). h(-1)) resulted in negligible changes in t he vasodilation caused by either dipyridamole or adenosine. However, a 10-fold greater theophylline dose significantly attenuated the vasodi lation caused by adenosine, yet the attenuation in vasodilation caused by dipyridamole remained negligible. In addition, dipyridamole caused a weakly preferential pulmonary vasodilation, whereas adenosine cause d a strongly preferential systemic vasodilation. These findings sugges t that dipyridamole dilates effectively both the pulmonary vasculature and the systemic vasculature via predominantly adenosine-independent mechanisms.