Tumor necrosis factor enhances glucose uptake by peripheral tissues

Anesthetized dogs received a constant intravenous infusion of tumor necrosis factor (TNF) or saline over 6 h. Glucose kinetics were studied by determining the rate of glucose turnover and hindlimb substrate flux. Cardiovascular responses were monitored and concentrations of counterregulatory hormones were also measured. TNF infusion caused a fall in blood glucose concentration from 4.6 ± 0.1 to 3.9 ± 0.2 mmol/l by 6 h (P < 0.05). This mild hypoglycemia was associated with increased circulating levels of cortisol, glucagon, and epinephrine. The rate of glucose production increased from 26.5 ± 2.1 to 32.5 ± 0.7 μmol · min^-1 · kg body wt^-1 (P < 0.05) over the 6-h infusion period; this response was associated with increased glucose disappearance (26.4 ± 2.2 to 32.7 ± 0.9 μmol · min^-1 · kg body wt^-1, P < 0.05) and enhanced clearance (5.7 ± 0.5 to 9.0 ± 0.6 ml · min^-1 · kg body wt^-1, P < 0.05). As blood glucose levels fell, hindlimb glucose uptake and glucose clearance increased markedly in TNF-infused animals as compared with controls despite a 50% fall in mean serum insulin concentration. The exchange of lactate, pyruvate, and total amino acid nitrogen across the hindlimbs was similar in both groups of animals. However, arterial concentrations of lactate and pyruvate rose to two to three times their initial values. The hypoglycemia associated with the infusion of TNF results from a disparity between the rate of glucose appearance and disappearance. There is an increased uptake of glucose across the hindlimb; this response appears to be independent of insulin concentrations and may be related to direct effects of TNF. Pyruvate and lactate concentrations rise because of altered central clearance and/or increased production in visceral tissues.