Metabolism of parenterally administered fat emulsions in the rat: studies of fatty acid oxidation with 1-13C- and 8-13C-labelled triolein.
To reassess the hypothesis that fatty acid catabolism occurs to completion via beta-oxidation, male Sprague-Dawley rats receiving continuous total parenteral nutrition (TPN) including 43% energy as fat were infused with [1-(13)C]- or [8-(13)C]triolein. Expired CO2 was collected continuously for 4 h and its 13C:12C ratio determined by isotope-ratio mass spectrometry. Bicarbonate retention was also assessed over 4 h by infusion of NaH14CO3 and measurement of the expired 14CO2. A possible loss of label from [8-(13)C]oleic acid from the citric acid cycle via labelled acetyl-CoA without oxidation to CO2 was assessed by infusing further animals with acetate labelled with 14C either at C atoms 1 or 2 and determination of its conversion to expired 14CO2. At isotopic steady state, 63.2 (SE 1.6)% (n 8) of the infused [1-(14)C]acetate and 46.0 (SE 1.2)% (n 8) of [2-(14)C]acetate was recovered as expired 14CO2. After correction for bicarbonate retention and non-oxidative isotope loss, 37.3 (SE 1.2)% (n 20) of the [1-(13)C]triolein was found to have been oxidized, whereas 32.6 (SE 1.0)% (n 20) of the [8-(13)C]triolein was oxidized (P < or = 0.01). The lower oxidation of the C atom at position 8 of oleic acid than that at position 1 indicates incomplete oxidative breakdown of the fatty acid after entering beta-oxidation.
Bäurle
W
W
Institute of Biological Chemistry and Nutrition, University of Hohenheim, Stuttgart, Germany.
Brösicke
H
H
Matthews
D E
DE
Pogan
K
K
Fürst
P
P
D000085:Acetates / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D019296:Capnography; D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D004041:Dietary Fats / Q000008:administration & dosage*; D005227:Fatty Acids / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010289:Parenteral Nutrition, Total; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D017693:Sodium Bicarbonate / Q000378:metabolism / Q000494:pharmacology; D018709:Statistics, Nonparametric; D014304:Triolein / Q000008:administration & dosage*
D000085:Acetates; D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D004041:Dietary Fats; D005227:Fatty Acids; D014304:Triolein; D017693:Sodium Bicarbonate