Measurement of non-steady-state free fatty acid turnover.
The accuracy of non-steady-state equations for measuring changes in free fatty acid rate of appearance (Ra) is unknown. In the present study, endogenous lipolysis (traced with [14C]-linoleate) was pharmacologically suppressed in six conscious mongrel dogs. A computer-responsive infusion pump was then used to deliver an intravenous oleic acid emulsion in both constant and linear gradient infusion modes. Both non-steady-state equations with various effective volumes of distribution (V) and steady-state equations were used to measure oleate Ra [( 14C]oleate). Endogenous lipolysis did not change during the experiment. When oleate Ra increased in a linear gradient fashion, only non-steady-state equations with a large (150 ml/kg) V resulted in erroneous values (9% overestimate, P less than 0.05). In contrast, when oleate Ra decreased in a similar fashion, steady-state and standard non-steady-state equations (V = plasma volume = 50 ml/kg) overestimated total oleate Ra (18 and 7%, P less than 0.001 and P less than 0.05, respectively). Overall, non-steady-state equations with an effective V of 90 ml/kg (1.8 x plasma volume) allowed the most accurate estimates of oleate Ra.
Jensen
M D
MD
Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905.
Heiling
V
V
Miles
J M
JM
D000818:Animals; D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid; D004285:Dogs; D005230:Fatty Acids, Nonesterified / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D007262:Infusions, Intravenous; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000378:metabolism; D008066:Lipolysis; D008954:Models, Biological; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D014280:Triglycerides / Q000378:metabolism; D014316:Tritium
D002250:Carbon Radioisotopes; D005230:Fatty Acids, Nonesterified; D008041:Linoleic Acids; D009829:Oleic Acids; D014280:Triglycerides; D014316:Tritium; D019301:Oleic Acid; D019787:Linoleic Acid