Site-specific effects of sympathectomy on the adrenergic control of lipolysis in hamster fat cells

Abstract

Regional variations in the response of adipose tissue to lipolytic stimuli have been suggested to be involved in the development of visceral adiposity-related morbidity and mortality. Moreover, studies in humans and in laboratory rodents such as hamsters have shown that the response of adipocytes to catecholamines depends on their anatomical origin. The aim of the present study was to investigate the relative involvement of the adrenal medulla and of the sympathetic nervous system on regional differences in the adrenergic control of lipolysis in isolated adipocytes from inguinal and epididymal adipose tissues. For this purpose, we carried out adrenal demedullation or chemical sympathectomy in hamsters. The results confirmed that epididymal adipocytes were significantly more responsive to a β-adrenergic stimulation than inguinal adipocytes (p ≤ 0.05). This site specificity could originate at a step distal to receptors since tissues exhibited a similar number of binding sites for [125I]cyanopindolol. No significant regional differences were observed in the α2-adrenergic antilipolytic response, with the exception of the clonidine EC50. A 14-day sympathectomy significantly increased the β-adrenergic lipolytic response only in inguinal adipocytes (p < 0.05), and increased the α2_adrenergic response only in epididymal adipocytes (p < 0.05). On the other hand, adrenal demedullation had no effect on both adrenergic pathways. These results suggest that the sympathetic tone of adipose tissues could be involved in the α2- and β-adrenergic site-specific response in hamster fat cells. The 33% increase of the β-response in inguinal fat cells and the 38% increase of the α2-response in epididymal fat cells also suggest that the sympathetic pathway favors the lipolytic activation of the epididymal adipose tissue.Key words: white adipose tissue, adrenal demedullation, α2-adrenergic receptors, β-adrenergic receptors.