title: Measurement of free fatty acid kinetics during non-equilibrium tracer conditions in man: implications for the estimation of the rate of appearance of free fatty acids.
abstract: BACKGROUND
  This study aimed to document the applicability and variability of free fatty acid (FFA) kinetic parameters during non-equilibrium and equilibrium tracer conditions in man.
  
  
  METHODS
  FFA kinetic parameters were assessed after an overnight fast in six healthy non-obese and three obese subjects as well as in three patients with non-insulin-dependent diabetes mellitus (NIDDM) by infusion of [14C]-palmitate of 60 min (study A) and 10 min duration (study B).
  
  
  RESULTS
  The kinetic parameters estimated from the upstroke and downstroke of the plasma FFA specific activity curve (non-equilibrium) were not statistically different within studies A and B. Furthermore, there were no significant differences in any of the FFA kinetic parameters between studies A and B. The averaged plasma levels of FFA obtained during the up- and downstroke from studies A and B were higher in obese subjects and NIDDM patients than in non-obese subjects (P < 0.01). The averaged total rate of appearance (TRa) of FFA was higher in obese subjects than in non-obese subjects (P < 0.02). The TRa and metabolic clearance rate (MCR), estimated from non-equilibrium conditions, were about 25% higher than the apparent values obtained from steady-state measurement in all subjects combined (P < 0.01), suggesting considerable recirculation of label from hydrolysis of labelled esterified fatty acids. Indeed, in three non-obese subjects, the radiolabel in esterified fatty acids was approximately 50% of labelled FFA at 60 min of label infusion. The coefficients of variation of the kinetic parameters were consistently larger in study A than in study B.
  
  
  CONCLUSIONS
  FFA kinetic parameters can be estimated with sufficient precision using non-equilibrium data from short-term labelled palmitate infusion. Short-term label infusion has the advantage that label recirculation is prevented and exposure to radiation is limited.
authors.affiliation: University Hospital Groningen, The Netherlands.
authors.forename: S C
authors.initials: SC
authors.lastname: Riemens
authors.forename: R P
authors.initials: RP
authors.lastname: Dullaart
authors.forename: E J
authors.initials: EJ
authors.lastname: Franssen
authors.forename: D A
authors.initials: DA
authors.lastname: Piers
authors.forename: W D
authors.initials: WD
authors.lastname: Reitsma
authors.forename: W J
authors.initials: WJ
authors.lastname: Sluiter
mesh_terms: D000328:Adult; D000368:Aged; D002250:Carbon Radioisotopes; D003924:Diabetes Mellitus, Type 2 / Q000097:blood; D005230:Fatty Acids, Nonesterified / Q000097:blood / Q000493:pharmacokinetics*; D006207:Half-Life; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D009765:Obesity / Q000097:blood; D019308:Palmitic Acid / Q000493:pharmacokinetics; D011849:Radioactive Tracers; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D002250:Carbon Radioisotopes; D005230:Fatty Acids, Nonesterified; D011849:Radioactive Tracers; D019308:Palmitic Acid