Catecholamine regulation of adipocyte lipolysis after surgery. The effect of surgical trauma on the regulation of lipolysis was studied in isolated fat cells obtained before and 24 hours after elective cholecystectomy in 12 patients who were not obese and who were healthy otherwise. Surgery was accompanied by a twofold increase of the basal rate of lipolysis and by a significant 50% elevation of the lipolytic effect of catecholamines. The actions of various agents that selectively stimulate lipolysis at different early or late steps in the cyclic adenosine monophosphate system beyond the adrenoreceptors were also increased about 50% after surgery (p less than 0.01). The properties of the beta-adrenoceptors were not altered by surgery, as assessed by radioligand binding and isoprenaline sensitivity. The antilipolytic properties of catecholamines (mediated by alpha 2-adrenoreceptors) were not influenced by cholecystectomy. Lipolysis was not altered in four subjects who had no surgery and who served as control subjects 24 hours after being given the same type of postoperative nutrition as patients who underwent cholecystectomy. We concluded that moderate surgical trauma is associated with increased lipolytic activity of fat cells. This is secondary to an enhanced ability of catecholamines to stimulate lipolysis because of a modification at the most distal steps in the cyclic adenosine monophosphate system, which may involve the protein kinase/hormone sensitive lipase complex. 