New
Insights into the Utilization of Medium-Chain Triglycerides by the
Neonate: Observations from a Piglet Model
Manuscript received
26 December 1996. Initial reviews completed 23 January 1997. Revision
accepted 17 February 1997.
Jack Odle
Department of Animal Science, North Carolina State University, Raleigh,
NC 27695
Because of their unique digestive and metabolic properties, medium-chain
triglycerides (MCT) are used in a variety of nutritional settings,
including use as a readily digestible energy source for the neonate.
This review examines recent findings from our laboratory related to
MCT digestion and metabolism that are drawn from a neonatal piglet
model, but which may be clinically relevant to human infants. We have
shown that MCT utilization improves rapidly with postnatal age (within
24 h), which is likely due to the ontogeny of pancreatic lipase. Additional
data delineate the dramatic effects of emulsification and fatty acid
chain length (within the medium-chain family) on utilization, with
the suggestion that triacylhexanoate is utilized at the highest rate.
Again, these effects are likely mediated via an increase in the kinetics
of digestion rather than metabolism. Indeed, using both in vitro and
in vivo radiotracer techniques, we were unable to detect metabolic
differences among even-chain fatty acid homologues. However, studies
with isolated hepatocytes have shown greater oxidation rates of odd-chain
fatty acids compared with even-chain homologues, in part as a reult
of the anaplerotic potential of propionyl-CoA arising from odd-carbon
fatty acid oxidation. In vivo radiotracer studies also showed an improvement
in octanoate oxidation to CO2, with a concomitant reduction in urinary
dicarboxylic acid excretion when colostrum-deprived piglets were supplemented
with L-carnitine. Further metabolic research led to the novel finding
that piglets have a very limited hepatic capacity to synthesize ketone
bodies, and that acetate may be a relatively important product of
hepatic fatty acid oxidation in this species.
Key words: medium-chain triglyceride, fatty acid metabolism, carnitine,
swine.
Articles
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