Omental and Epigastric Adipose Tissue Lipolytic Activity in Human Obesity

 

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Summary

It has been shown that visceral obesity is associated with an increased incidence of hyperinsulinemia. In such a condition, hyperinsulinemia could be due to an increased lipolytic activity of omental adipose tissue (AT), through an enhanced portal flux of FFA. The purpose of our study was to evaluate the lipolytic activity of omental and epigastric AT obtained from morbid obese patients either with prevalently visceral or subcutaneous abdominal fat accumulation, evaluated by computerized tomography. The relationship between plasma insulin values and in vitro lipolytic activity in both tissues was studied. Thirteen visceral (VO) and 13 subcutaneous (SO) obese patients, matched for sex and body mass index, undergoing vertical banded gastroplasty, were studied. Before surgery, in each patient an OGTT was performed. During surgery, samples of epigastric subcutaneous and omental AT were obtained for evaluation of fat cell weight (FCW) and basal, noradrenaline 10^-5 M and isoprenaline 10^-5 M induced lipolytic activities. No significant differences in basal lipolysis were found between the two types of obesity, both in omental and in epigastric AT. In omental AT, a higher noradrenaline and isoprenaline induced lipolysis was observed in VO than in SO. Isoprenaline induced lipolysis of omental AT (expressed per cell surface area) correlated directly with FCW. VO patients showed plasma insulin values after OGTT significantly higher than SO patients. In the whole group of patients, independently from fat distribution, significant correlations were found between the incremental areas of the plasma insulin curve during OGTT and the noradrenaline and isoprenaline induced lipolytic activities both in omental and epigastric adipose tissue. In omental adipose tissue, these correlations were found only in VO and not in SO patients. In conclusion, VO patients showed a higher noradrenaline induced lipolytic activity of omental AT than SO patients. This increased catecholamine stimulated lipolysis is related to the higher omental fat cell size characteristic of the visceral obese patients. A relationship exists between hyperinsulinemia and lipolytic activity of epigastric AT in the obese patients, independently from fat distribution, while in omental AT, such a relationship was found only in VO patients.