Adrenergic regulation of adipocyte metabolism

Five adrenoceptor (AR) subtypes (Pi, P2, 03> oc2 and oti), are involved in the control of white and brown fat cell function. A number of metabolic events are controlled by the adrenergic system in fat cells. The stimulatory effect of catecholamines on lipolysis and metabolism is mainly connected to increments in cAMP levels, cAMP protein kinase activation and phosphorylation of various target proteins. Norepinephrine and epinephrine operate through differential recruitment of o^and p*-AR subtypes on the basis of their relative affinity for the different subtypes (the relative order of affinity is (X2 > Pi 22 |32 > P3 for norepinephrine). Antagonistic actions at the level of cAMP production exist between 0C2and p r , p2and p3-AR-mediated lipolytic effects in human white fat cells. The role of fat cell (X2-ARs, which largely outnumber p-ARs in fat cells of certain fat deposits, in human and primate has never been clearly understood. The other AR type which is not linked to lipolysis regulation, the ocrAR, is involved in the control of glycogenolysis and lactate production. Pharmacological approaches using in-situ microdialysis and selective oc2and P-AR agonists and antagonists have revealed sexand tissue-specific differences in the adrenergic control of fat cell function and nutritive blood flow in the tissue surrounding the microdialysis probe.