Adenosine is Required for Myocardial Insulin Responsiveness In Vivo

The adenosine-receptor antagonist 8-phenyltheophylline (8-PTH) was used to study the role of endogenous adenosine in modulating insulin-stimulated myocardial glucose uptake (MGU) in vivo. Dogs were surgically instrumented under pentobarbital sodium anesthesia to measure hemodynamics and obtain blood samples for determinations of oxygen and glucose concentrations. Myocardial uptake of these substances was calculated as the product of the appropriate arterial–coronary sinus differences and circumflex blood flow. The response to insulin was determined with the hyperinsulinemic-euglycemic clamp technique. During insulin infusion, MGU increased from 3.12 ± 0.8 to 9.20 ± 1.8 mg/min (mean ± SE). In contrast, insulin failed to increase MGU when 8-PTH was being infused into the circumflex artery. These results demonstrate that some degree of adenosine-receptor–mediated activity is required for insulin to stimulate myocardial glucose uptake. It is suggested that the presence of adenosine at its receptor may be an important factor during conditions in which myocardial insulin resistance may develop.