Ws. Swails et al., GASTRIC-EMPTYING IN HUMANS - INFLUENCE OF DIFFERENT REGIMENS OF PARENTERAL-NUTRITION, JPEN. Journal of parenteral and enteral nutrition, 20(3), 1996, pp. 240-242
Controversy exists in the literature regarding the effect of parentera
l nutrition on appetite. Earlier, several authors showed that healthy
adult males receiving IV nutrition reduced their voluntary food intake
by an amount that approximated 80% of the IV calories.(1) This findin
g suggested a postabsorptive control of oral food intake. In view of t
his observation, the authors of this study sought to answer two questi
ons: does parenteral nutrition decrease gastric emptying and does the
administration of branched-chain amino acids (BCAAs) alter the rate of
gastric emptying? Nine healthy male volunteers between the ages of 20
and 31 years with a mean weight of 72 +/- 10 kg were studied. Basal e
nergy requirements were calculated using the Harris-Benedict equation
and were estimated to be approximately 1765 kcal/d. All subjects were
maintained on a diet consisting solely of an oral liquid supplement co
mposed of 40% carbohydrate, 20% protein, and 40% fat (Ensure, Ross Lab
s, Columbus, OH). Each subject served as his own control and was studi
ed three times. The first 6 days of each study period were spent at ho
me consuming the oral liquid supplement. On the sixth day, subjects we
re admitted to the hospital, and after an overnight fast, one of three
parenteral solutions was infused over a 12-hour period. The parentera
l formulas consisted of Ringer's lactate, a standard parenteral soluti
on, or a parenteral solution in which half of the amino acids used in
the standard parenteral solution were replaced with BCAAs. The latter
two formulas consisted of 40% carbohydrate, 20% protein, and 40% fat a
nd supplied 85% of the subjects' estimated basal energy needs. After 6
hours of the parenteral infusion, subjects consumed 500 mt of technet
ium-labeled Ensure within a 2-minute period, and gastric emptying was
then measured by scintigraphy. In addition, blood samples were drawn 5
hours after initiation of the IVinfusion and 45 minutes after consump
tion of the oral supplement for analysis of plasma glucose, insulin, g
lucagon, triglyceride, and free fatty acid levels. The rate of gastric
emptying within the first 10 minutes after ingestion of the oral supp
lement was most rapid when Ringer's lactate was infused (radioactivity
lost from stomach was 1.63%/min). The rate slowly decreased over the
subsequent 50 minutes until it reached a steady rate of 0.46%/min. The
initial rate of gastric emptying was significantly slower with the st
andard parenteral formula (0.67%/min) compared with the Ringer's lacta
te. However, the rate was not significantly different than that of the
Ringer's lactate after 50 minutes (0.48%/min). The initial gastric em
ptying rate during infusion of the BCAA solution (0.83%/min) was betwe
en that of the Ringer's lactate and the standard parenteral solution.
Fifty minutes after infusion of the BCAA solution, the rate decreased
to 0.43%/min; this rate was slightly lower than that observed with the
other two IV solution at this time point (Table I). Mean serum glucos
e levels never exceeded 122 mg/dL, and there was no correlation betwee
n glucose concentrations and the rate of gastric emptying. There were
no significant changes in free fatty acid or plasma glucagon concentra
tions. These results demonstrate that gastric emptying is delayed in n
ormal healthy male subjects receiving 42.5% (similar to 750 kcal) of t
heir estimated basal energy requirements from parenteral nutrition ove
r a B-hour period. In addition, the authors propose that the BCAA pare
nteral solution did not delay gastric emptying to the same degree as t
he other two parenteral solutions due to the ability of BCAAs to decre
ase serotonin synthesis in the brain. Serotonin is a neurotransmitter
known to regulate food intake and inhibit gastric emptying. Thus the a
uthors suggest that providing parenteral solutions enriched with BCAAs
may improve voluntary food intake during and after parenteral nutriti
on administration. They conclude that the reduction in oral intake fre
quently seen in patients receiving parenteral nutrition may be a refle
ction of the parallel reduction in the rate of gastric emptying rather
than a result of existing disease.