Amino acid use by the gastrointestinal tract of sheep given lucerne
forage.
Macrae, John C., Les A. Bruce, David S. Brown & A. Graham Calder.
Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, Scotland,
U.K.
APStracts 3:0113G, 1996.
Essential amino acid (EAA) utilisation by gastrointestinal tract (GIT)
tissues has been investigated in sheep given 800 and 1200 g/d lucerne
pellets. Animals prepared with indwelling catheters into the aorta
and the portal drained viscera plus cannulae into the small intestine
were infused with mixed [U-13C]AA or [1-13C]leucine tracers into the
jugular vein or directly into the small intestine. GIT sequestration
of EAA from arterial and luminal AA pools was determined from tracer
and tracee arterio-portal concentration differences at both levels of
intake. Proportional tracer 13C EAA extraction of the arterial
supply, on first pass across the GIT during jugular infusion, ranged
from 0.063 for histidine to 0.126 for leucine. Recovery of
intestinally infused tracer 13C EAA at the portal vein ranged from
0.61 for histidine to 0.83 for valine. These data were independent of
intake. Calculated rates of tracee sequestration by GIT tissues
represented 0.45-0.65 of whole body EAA flux, except for histidine
where the values were much lower (0.25-0.32). With the exception of
phenylalanine, more than 0.8 of the EAA used by the GIT was extracted
from circulating blood, thus questioning the concept that GIT tissues
make preferential use of EAA during absorptive metabolism so
restricting supply to peripheral tissues such as skeletal muscle
(growth) or the mammary gland (lactation). Rather the GIT seems to
compete very successfully with these tissues for circulating blood
EAA.
Received 17 January 1996; accepted in final form 23 May 1996.
APS Manuscript Number G24-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96