Potentiation by Glucose of Lipolytic Responsiveness of Human Adipocytes

The effect of glucose on lipolytic regulation was studied in isolated human adipocytes. Glucose enhanced adipocyte glycerol release in the presence and absence of the β-adrenergic agent ritodrine by 150–200% of control rates. The glucose effect was maximal at just >1 mM glucose and could not be attributed to prevention of a time-dependent decline in lipolysis. Glucose not only increased lipolytic stimulation at each of several concentrations of ritodrine but also enhanced the sensitivity to stimulation at low concentrations of the agent. Ritodrine-stimulated lipolysis was inhibited by insulin by 50–60%; although glucose increased absolute rates of lipolysis, it did not affect the relative inhibition of lipolysis by insulin or the sensitivity to the hormone. In investigating a possible cause of the glucose effect on lipolysis, it was found that the addition of adenosine deaminase increased lipolytic rates in the absence of glucose and blunted the relative stimulation of lipolysis by glucose, the latter implicating extracellular adenosine in the mechanism of the glucose effect.