Effects of TNF-alpha on glucose metabolism and lipolysis in adipose tissue and isolated fat-cell preparations

We hypothesized that exposure to tumor necrosis factor-alpha (TNF-alpha) would significantly increase lactate production by adipose-tissue (AT) fragments and isolated adipocytes. We therefore examined the effects of TNF-alpha on the metabolism of epididymal AT explants during 24-hour tissue incubation. We also studied the effects of this 24-hour TNF-alpha tissue exposure on subsequent glucose metabolism and lipolysis by isolated adipocytes. Glycerol release into the medium was significantly increased (50%, P =.027) by exposure of the AT fragments to TNF-alpha (4 nmol/L) for 24 hours. During this time, glucose uptake from the medium and lactate release into the medium tended to increase, whereas leptin release into the medium tended to decrease, but these effects of TNF-alpha were not statistically significant. After the 24-hour AT-explant incubation, adipocytes were isolated by means of collagenase digestion from the AT fragments and subsequently tested in a short-term (60-minute) metabolic incubation. Prior exposure to TNF-alpha resulted in a significant increase in adipocyte glycerol release (P =.044), total glucose metabolism (P =.019), and lactate production (P =.037). With the exception of lactate, TNF-alpha produced no significant stimulation of the metabolites of glucose. The pattern of glucose metabolism elicited by TNF-alpha exposure differs from that usually attributed to a lipolytic hormone and suggests that the effects of TNF-alpha on glucose metabolism involve pathways separate from, or in addition to, its effects on lipolytic stimulation.