The present work was planned to study the effects of changes in lipid metabolism irrespective of FFA concentrations (FFA) on the regulation of oxidative and nonoxidative disposal of a glucose infusion during hyperinsulinaemia. Fifteen normal volunteers participated in the 3 protocols, in which 1) Intralipid 2) beta-pyridylcarbinol or 3) isotonic saline were infused during 2 hours. Thereafter, these infusions were discontinued and a two-hour euglycaemic hyperinsulinaemic clamp was performed. All three studies were carried out in combination with indirect calorimetry to measure glucose uptake, and oxidative and nonoxidative glucose disposal (corresponding essentially to glucose storage). Plasma FFA concentrations were 508+/-34, 601+/-43 and 546+/-45 mumol/l in the basal state during the Intralipid, beta-pyridylcarbinol and control protocols. It increased to 960+/-71 mumol/l after the Intralipid infusion, fell to 246+/-17 mumol/l after the beta-pyridylcarbinol infusion, vs 600+/-48 mumol/l in the control. At the end of the glucose-insulin clamp the values were low in the 3 protocols: 263+/-17, 233+/-19 and 204+/-14 mumol/l. Intralipid infusion prior to the clamp protocol induced a suppression of both insulin-mediated glucose uptake (4.91+/-0.46 (Intralipid) vs 6.83+/-0.63 mg. kg-1. min-1 (saline)) and storage (1.61+/-0.34 vs 2.99+/-0.53 mg. kg-1. min-1) while beta-pyridylcarbinol infusion induced an increased insulin-mediated glucose uptake (8.58+/-0.37 mg. kg-1. min-1) and in glucose storage (4.29+/-0.31 mg. kg-1. min-1)(p less than 0.5 vs Intralipid). These changes occurred even though FFA plasma concentrations were similar in the 3 experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)