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Calcium infusion induces myocardial ischaemia in patients with coronary artery disease by a mechanism possibly adenosine mediated.

In the first part of the study five healthy volunteers were submitted to i.v. infusion of 0.2 mM.kg-1 b.w. of calcium gluconate over 20 min. Total calcium (atomic absorption method), ionized calcium (ion-selective electrode method) and adenosine (HPLC technique) were measured at the following times: 0 (basal), 5, 10, 15, 20 (end of infusion), 25, 30, 35, and 50 min. The increase in total and ionized calcium serum levels was associated with a significant increase in adenosine plasma levels (from 207 +/- 41 to 362 +/- 63 nM.l-1, P < 0.001). Since the increase in adenosine plasma levels, obtained either with adenosine or dipyridamole (an adenosine reuptake inhibitor), has been used to test the coronary reserve in coronary artery disease (CAD) patients, in the second part of the study we compared the effects of calcium infusion with dipyridamole in 15 subjects. Pharmacological stress tests were evaluated by monitoring two-dimensional echocardiography and ECG. Ten patients had positive results with both the dipyridamole stress test and the calcium infusion. Our results show that calcium infusion induces an increase in adenosine plasma levels that can elicit a dipyridamole-like coronary steal, thus suggesting the central role of extracellular adenosine in myocardial ischaemia.