Changes in the adrenergic control and the rate of lipolysis of isolated human adipose tissue during fasting and after re-feeding.

The influence of changes in nutritional state on lipid mobilization has been investigated, using subcutaneous fat portions removed from 8 obese patients submitted to fasting for one week. The maximal rise in the tissue level of cyclic AMP (cAMP) and the rate of glycerol release were determined when adipose tissue was exposed to noradrenaline (6 X 10(-6) mol/1), isopropylnoradrenaline (6 X 10 (-6) mol/1) or none of the agents (basal medium). Fasting resulted in significant increases in the tissue level of cAMP and the rate of lipolysis in adipose tissue unexposed to lipolytic agents. Noradrenaline decreased the level of cAMP, in contrast to isopropylnoradrenaline, and significantly inhibited the rate of lipolysis during fasting. These noradrenaline effects were abolished by the simultaneous presence of phentolamine (13 mmol/1) in the incubation medium. Re-feeding with Meritene for one day resulted in a diminished rate of basal lipolysis, whereas the cAMP level was unaffected. The response of the cAMP accumulation to isopropylnoradrenaline was further augmented by re-feeding. Noradrenaline produced a significant rise in the level of cAMP and significantly stimulated the rate of glycerol production. It is concluded that the nutritional changes are of significance for the adrenergic regulation of lipolysis as indicated by the response of cAMP to the catecholamines. In pharmacological terms, fasting for one week resulted in increased alpha-as well as beta-adrenergic responsiveness. Increased basal lipolysis during fasting may be related to an increased level of cAMP or a direct activation of lipase.