Systemic exchangeability of enteral leucine: relationship to plasma flux

Journal Article · Fri Apr 01 04:00:00 EST 1988 · Am. J. Physiol.; (United States)

OSTI ID:7191439

Istfan, N W; Ling, P R; Bistrian, B R; Blackburn, G L

The exchangeability of enterally infused leucine within the systemic compartment was estimated in fasted and fed rats using L-(1-/sup 14/C)leucine as a tracer. The experimental design consisted of enteral and parenteral feedings with intravenous or intragastric tracer infusions. During continuous intragastric feeding, only 73 +/- 6% (SE) of the intragastric leucine tracer infusion was accounted for in the systemic circulation. When comparing intravenous vs. intragastric tracer, the estimate of the contribution of protein breakdown to plasma leucine flux was 6 +/- 1 (SE) mumol.h-1.100 g-1 and 18 +/- 3 (SE) mumol.h-1.100 g-1 (P less than 0.01), respectively, for the two routes of administration. Correction of enteral input (either isotope or total leucine), by a factor of 27% for first-pass extraction, eliminated all significant differences in plasma leucine kinetics. Of the 27% of enterally infused tracer not appearing systemically, only 3% could be accounted for in newly synthesized protein in the liver. The remainder is hypothesized to represent first-pass utilization of leucine in intestinal protein synthesis and other metabolic pathways in the splanchnic bed. In contrast, systemic appearance of enteral leucine was essentially complete in the fasted rats, indicating less splanchnic metabolism of leucine in this state. These data indicate that significant error can result in estimating the contribution of endogenous protein breakdown to plasma leucine flux during feeding if the systemic exchangeability of dietary leucine is not considered.

• Research Organization: Cancer Research Institute, Boston, MA (USA)
• OSTI ID: 7191439
• Journal Information: Am. J. Physiol.; (United States), Journal Name: Am. J. Physiol.; (United States) Vol. 254; ISSN AJPHA
• Country of Publication: United States
• Language: English

Related Subjects

550501* -- Metabolism-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANIMALS
BIOLOGICAL PATHWAYS
BODY
CARBON 14 COMPOUNDS
CARBOXYLIC ACIDS
DIGESTIVE SYSTEM
FASTING
GLANDS
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
LEUCINE
LIVER
MAMMALS
METABOLISM
MUSCLES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANS
RATS
RODENTS
TRACER TECHNIQUES
VERTEBRATES