Regulation of lypolysis in white adipose tissues of lean and obese Zucker rats

Obese Zucker rat is often used as a model of genetic obesity to understand the mechanism of the development of obesity. In the present work, in order to better understand the regulation of lipolysis in the Zucker rat, the lipolytic activities of adipocytes isolated from different adipose depots of lean and obese Zucker rats, in the basal state or after catecholamine stimulation have been measured. The obese Zucker rat presents hyperinsulinemia without hyperglycemia and with elevated plasma free fatty acids, suggesting a dyslipidemia. Morphological studies of three adipose deposits show a marked hypertrophic and hyperplastic type of obesity, much pronounced in the subcutaneous depot. In the current study we show that the basal lipolytic rate is higher in adipocytes from each deposit of obese rats (when results are corrected for cell surface area). This finding, associated with the increase of all deposits, could contribute to the elevated plasma FFA observed. Investigation of the responsiveness of dibutyril cAMP (DBcAMP) points out that the defect in the NE responsiveness is essentially located at post-receptor level. Nevertheless, a receptor defect could not be excluded as suggested by a decrease of the beta-ARs observed in all deposits. Our study points out that the lipolytic resistance to catecholamines in adipose tissue of obese Zucker rats appears to counteract the increase in the lipolytic rate, in order to moderate the increase in plasma FFA levels that may contribute to the hyperinsulinemia observed, characteristic of an insulino-resistant state.