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In the first part of the study 5 control subjects were submitted to iv infusion of 0.2 mM/kg of calcium gluconate in 20 min. Total calcium (atomic absorbtion method), ionized calcium (ion-selective electrode method) and adenosine (HPLC technique) were measured at the following times: 0 (baseline), 5, 10, 15, 20 (end of infusion), 25, 30, 35, and 50 min. The increase of total and ionized calcium serum levels was associated with a significant increase of adenosine plasma levels (from 207 +/- 41 to 362 +/- 63 nM, p < 0.001). Since the increase of adenosine plasma levels, obtained either with adenosine or dipyridamole (an adenosine reuptake inhibitor), has been used to test the coronary reserve in patients with coronary artery disease (CAD), in the second part of the study we compared the effects of calcium infusion with dipyridamole in 15 CAD subjects. Pharmacological stress tests were evaluated by monitoring two-dimensional echocardiography, ECG, heart rate, blood pressure and rate-pressure product. Ten patients were positive both to dipyridamole stress test and to calcium infusion, ad demonstrated by the onset of new areas of transient asynergy in the same myocardial regions. Dipyridamole infusion determined a significant increase in heart rate and rate pressure-product in all patients (both in positive and in negative), whereas calcium induced a slight, not significant decrease of these parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Purine metabolism has been much investigated in human erythrocytes, both for the interest focused on this peculiar cell biochemistry, and four purine pathological implications in man. Most mammalian red blood cells lack de novo purine synthesis, and are completely dependent on base salvage pathway for their purine nucleotide requirement. Besides, human erythrocyte is devoid of some purine interconversion enzymes, thus becoming dependent on external supply of bases and nucleosides, particularly the adenylic ones. Red blood cell purine metabolism is very active, owing to its great need for nucleotides, and seems to aim greatly at the preservation of synthesized nucleotides against catabolic events. Available data on purine enzyme kinetic parameters and regulation, substrate and product cellular concentration and uptake are reviewed.