Effect of short-term fasting on the lipolytic responses to theophylline

We investigated the hypothesis that the increase in lipolysis that occurs in short-term (86-h) fasting is due to a decreased inhibitory influence of adenosine. In normal volunteers who fasted for 14 and 86 h, the response to adenosine receptor blockade was assessed by the infusion of theophylline at a rate sufficient to produce plasma concentrations (30 μM) that blocked adenosine receptors but that were well below the threshold for inhibition of phosphodiesterase. Lipolysis was assessed by determining the rate of appearance of glycerol using D-5-glycerol infusion. Fatty acid flux was also determined by means of [1-¹³C]palmitate infusion, and total fatty acid oxidation was determined by indirect calorimetry. There was a mild stimulatory effect of theophylline on lipolysis at 14 h. After the subjects fasted for 86 h, theophylline infusion caused a much greater increase in both lipolysis and fatty acid oxidation. These results suggest that the inhibitory effect of adenosine on lipolysis is increased during short-term fasting.