Role of alpha-adrenoceptors for adipocyte size in man

Catecholamines have dual effects on lipid mobilization in man. Lipolysis is stimulated via beta-adrenoceptors and inhibited via alpha 2-adrenoceptors. The relationship between fat-cell size and catecholamine-induced lipolysis (expressed per cell surface area) was investigated in vitro in subcutaneous adipocytes of thirty-five non-obese subjects between 1 month and 45 years of age. Fat-cell volume showed a positive correlation with noradrenaline-induced lipolysis (r = 0.7). Furthermore, fat-cell size showed a negative correlation with the alpha 2-effect of noradrenaline (r = 0.8) but no correlation with the beta-effect of the hormone (r less than 0.1). Although age showed a positive correlation with noradrenaline-induced rate of lipolysis (r = 0.6) it did not contribute to the relationship between cell size and the catecholamine effect. There was no relationship between adipocyte size and the basal (unstimulated) rate of lipolysis (r less than 0.1). In conclusion, ageing in non-obese subjects is associated with enlargement of fat-cell size and enhancement of the lipolytic effect of catecholamines. The latter is due to diminished alpha 2-anti-lipolytic effect of the hormones. This modulation of the alpha 2-adrenoceptor activity may be of importance for the regulation of adipocyte size in man.