Adenosine potentiates insulin-stimulated myocardial glucose uptake in vivo

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Abstract
Myocardial adenosine (ADO) has long been regarded as a regulator of coronary blood flow. In other tissues, such as adipose and skeletal muscle, much attention has focused on the role of ADO as a metabolic regulator of the actions of insulin. In the present study, we determined the effect of ADO infusion on insulin-stimulated myocardial glucose uptake (MGU). Mongrel dogs of either sex were instrumented to obtain arterial-coronary sinus differences for glucose, lactate, and oxygen. These were multiplied by circumflex artery blood flow (Q) to obtain uptake values. Measurements were made before and during hyperinsulinemic (4 U/min)-euglycemic clamp (clamp) with intracoronary infusions of saline, ADO, adenosine deaminase (ADA), or nitroprusside (NP). During clamp, MGU increased from a basal value of 3.0 .+-. 0.8 mg/min (mean .+-. SE) to 5.53 .+-. 0.8 mg/min. Adenosine infusion potentiated this response, raising MGU further to 9.02 .+-. 1.1 mg/min while not significantly affecting lactate or oxygen uptakes. Infusion of ADA confirmed the specificity of the response by blocking the metabolic effect of exogenously infused ADO. When Np was infused, Q increased significantly without altering MGU, indicating that the metabolic response to ADO was independent of the changes it caused in Q. A dose-response relationship existed between ADO and insulin-stimulated MGU. The metabolic response to ADO was more sensitive than the vasodilator response. It is concluded that ADO acts as a regulator of insulin in heart. This metabolic regulation occurs independent of changes in coronary blood flow.