Abstract
We previously characterized human duodenal uptake of C in vitro as a combined active (KT 558 μ M) and passive system (Gastro 91:10, 1986). To ascertain the response to physiologic or pharmacologic doses, serial intrajejunal and plasma levels were measured for 6 hr after either a hamburger meal [200 μmol free C (FC); 139 μmol short-chain acyl ester (SCAC)] or an oral dose of L-C (50 mg/kg). In vivo jejunal absorption was studied by the triple-lumen perfusion technique.
RESULTS: Fasting luminal levels were 9 μM FC and 15 μM SCAC. The meal raised these fractions to 209 μM FC and 130 μM SCAC at 1 hr reflecting Its composition but did not affect plasma levels. The drug dose sharply increased jejunal levels to 20,660 μM FC and 3,780 μM SCAC at ½ hr falling to near baseline by 6 hr. The SCAC portion remained between 14-25% possibly representing mucosal metabolism. Although plasma FC levels doubled to 67 μM at 3-4 hr, the SCAC portion remained between 18-23%. Preliminary in situ perfusions indicate that net C flux was 58 nmol/min/30 cm gut segment at 20 μM and 484 nmol/min/30 cm at 200 μM; thus demonstrating net absorption at fasting and meal concentrations.
CONCLUSION: Absorption of C occurs predominantly by active transport under physiologic conditions and by passive diffusion during drug administration. The presence of considerable SCAC under both conditions suggests that its absorption is of potential physiologic significance.
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Li, B., Lloyd, M., Shug, A. et al. JEJUNAL CARNITINE (C) LEVELS AND ABSORPTION IN HUMANS. Pediatr Res 21 (Suppl 4), 272 (1987). https://doi.org/10.1203/00006450-198704010-00629
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DOI: https://doi.org/10.1203/00006450-198704010-00629