Impaired glucose tolerance in the absence of adenosine A1 receptor signaling

OBJECTIVE - The role of adenosine (ADO) in the regulation of glucose homeostasis is not clear. In the current study, we used A1-ADO receptor (A1AR)-deficient mice to investigate the role of ADO/A1AR signaling for glucose homeostasis. RESEARCH DESIGN ANDMETHODS - After weaning, A1AR ^-/- and wild-type mice received either a standard diet (12 kcal% fat) or high-fat diet (HFD; 45 kcal% fat). Body weight, fasting plasma glucose, plasma insulin, and intraperitoneal glucose tolerance tests were performed in 8-week-old mice and again after 12-20 weeks of subsequent observation. Body composition was quantified by magnetic resonance imaging and epididymal fat-pad weights. Glucose metabolism was investigated by hyperinsulinemic-euglycemic clamp studies. To describe pathophysiological mechanisms, adipokines and Akt phosphorylation were measured. RESULTS - A1AR ^-/- mice were significantly heavier than wild-type mice because of an increased fat mass. Fasting plasma glucose and insulin were significantly higher in A1AR ^-/- mice after weaning and remained higher in adulthood. An intraperitoneal glucose challenge disclosed a significantly slower glucose clearance in A1AR ^-/- mice. An HFD enhanced this phenotype in A1AR ^-/- mice and unmasked a dysfunctional insulin secretory mechanism. Insulin sensitivity was significantly impaired in A1AR ^-/- mice on the standard diet shortly after weaning. Clamp studies detected a significant decrease of net glucose uptake in A1AR ^-/- mice and a reduced glucose uptake in muscle and white adipose tissue. Effects were not triggered by leptin deficiency but involved a decreased Akt phosphorylation. CONCLUSIONS - ADO/A1AR signaling contributes importantly to insulin-controlled glucose homeostasis and insulin sensitivity in C57BL/6 mice and is involved in the metabolic regulation of adipose tissue.