Adenosine and lipolysis.

The present review briefly summarizes work from the author's laboratory aiming at the clarification of the role played by adenosine in the regulation of adipose tissue circulation and metabolism. Studies on isolated fat cells demonstrate that adenosine, in mumolar concentrations, can inhibit lipolysis induced by eg noradrenaline. The effect appears to be due to inhibition of cyclic AMP formation. Studies of subcutaneous adipose tissue in situ also demonstrate the effect of exogenous adenosine on lipolysis. Furthermore, adenosine causes vasodilation and inhibition of noradrenaline release from sympathetic nerve endings. The actions of adenosine are antagonized by theophylline and other methylxanthines in concentrations lower than those required to inhibit cyclic AMP breakdown. It is shown that adenosine is normally present in adipose tissue in approximately 0.3 microM concentration and that the level is increased by sympathetic nerve stimulation. From a quantitative comparison of adenosine levels and dose-effect relationships as well as from pharmacological studies it is concluded that adenosine is a physiological regulator of adipose tissue circulation and lipolysis, while the physiological role of adenosine as a transsynaptic modulator of noradrenaline release remains to be established.