ADENOSINE AND DIPYRIDAMOLE ACTIONS AND INTERACTIONS ON ISOLATED CORONARY ARTERY STRIPS OF CATTLE

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Abstract
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 o.d.), raised to a moderate level of tone with potassium, responded with relaxation to low concentrations of adenosine. Dipyridamole, over a broad concentration range (6.0 × 10−8‐2.0 × 10−5M), enhanced these responses, shifting the adenosine concentration‐response curve (3.7 × 10−8‐1.1 × 10−4M) considerably to the left. In contrast, inhibitory concentration‐response curves to sodium nitrite and to noradrenaline were not materially altered by dipyridamole. Studies of the uptake of [3H] ‐adenosine revealed a rapid uptake of the nucleoside by coronary artery strips, which was inhibited by dipyridamole (6.0 × 10−8‐2.0 × 10−5M); but this may not be sufficient to account fully for the observed sensitization. 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.

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