Adenosine and dipyridamole actions and interactions on isolated coronary artery strips of cattle.

1 The actions and interactions of adenosine and dipyridamole were investigated on isolated strips of coronary arteries of beef cattle. It was found that small diameter arteries (about 0.5-1.0 mm o9d.), raised to a moderate level of tone with potassium, responded with relaxation to low concentrations of adenosine. 2 Dipyridamole, over a broad concentration range (6.0 X 10(-8)-2.0 X 10(-5)M), enhanced these responses, shifting the adenosine concentration-response curve (3.7 X 10(-8)-1.1 X 10(-4)M) considerably to the left. In contrast, inhibitory concentrations-response curves to sodium nitrite and to noradrenaline were not materially altered by dipyridamole. 3 Studies of the uptake of [3H]-adenosine revealed a rapid uptake of the nucleoside by coronary artery strips, which was inhibited by dipyridamole (6.0X 10(-8)-2.0X10(-5)M); but this may not be sufficient to account fully for the observed sensitization. 4 It is concluded that the regulation of adenosine responses and the action of dipyridamole in the heart involve a more direct association with coronary vascular tissue than has been previously appreciated.