Evidence for dual control mechanism regulating hepatic glucose output in nondiabetic men.

We previously reported a fall in hepatic glucose output (HGO) during sleep accompanied by reductions in glucose utilization (Rd) and free fatty acids (FFAs). This study was undertaken to determine the potential role of changes in Rd and FFA on HGO in nondiabetic men. To determine if the fall in HGO during sleep could be reversed by FFA elevation, seven nondiabetic men underwent [3-3H]glucose infusions from 2200 to 0800, with heparin (90 mU.kg-1.min-1) added at 0200. Glucose appearance (Ra) fell from 11.7 +/- 1.1 at 2430 to 8.9 +/- 0.8 mumol.kg-1.min-1 (P less than 0.05) at 0200. The fall in Ra was associated with decreases in FFA (0.57 +/- 0.10 to 0.48 +/- 0.07 mM) and glycerol (0.08 +/- 0.01 to 0.06 +/- 0.01 mM). Infusion of heparin significantly increased FFA and glycerol (1.09 +/- 0.21 and 0.11 +/- 0.01 mM, respectively, P less than 0.01) and resulted in a significant fall in plasma alanine, suggesting that gluconeogenesis had been increased. However, rates of glucose turnover were indistinguishable from overnight studies without heparin. In additional studies (n = 6), intralipid and heparin-induced FFA elevation (from 0.61 +/- 0.07 to 0.95 +/- 0.05 mM, P less than 0.01) stimulated gluconeogenesis ([U-14C]alanine to glucose) twofold (188 +/- 22% increase compared to 114 +/- 6% in saline control studies, P less than 0.01). However, despite increasing gluconeogenesis, overall HGO did not change (10.6 +/- 0.5 vs. 10.7 +/- 0.6 mumol.kg-1.min-1) during lipid infusion.(ABSTRACT TRUNCATED AT 250 WORDS)