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[13C]Acetate oxidation in infants after oral versus rectal administration: a kinetic model
Insights
Rectal administration of volatile fatty acids (VFAs) leads to faster oxidation in the colon compared to oral intake. This suggests direct utilization of VFAs within the large bowel for infants.
Area of Science:
- Gastroenterology
- Metabolic Research
- Pediatric Nutrition
Background:
- Volatile fatty acids (VFAs) are crucial energy substrates in the large bowel.
- Understanding VFA metabolism is important for infant gut health, especially post-diarrhea.
Purpose of the Study:
- To investigate the metabolic fate and oxidation rates of volatile fatty acids (VFAs) administered rectally versus orally.
- To compare the absorption and utilization pathways of VFAs in the large bowel.
Main Methods:
- Utilized 13C-labeled acetate administered rectally and orally to infants recovering from diarrhea.
- Collected and analyzed breath samples for 13C enrichment in carbon dioxide (CO2) over 4 hours.
- Applied multicompartmental modeling (SAAM-27) to fit 13C breath recovery data.
Main Results:
- Rectal acetate administration showed a simpler metabolic model with direct oxidation in the administration compartment.
- Oral acetate administration required a more complex model involving systemic absorption and mixing before oxidation.
- 13C-labeled acetate was oxidized significantly faster when administered rectally compared to orally.
Conclusions:
- Volatile fatty acids (VFAs) are directly utilized within the colon.
- Rectal administration bypasses systemic absorption, allowing for more rapid VFA oxidation.
- This highlights a potential pathway for direct nutrient delivery and utilization in the large intestine.
Abstract:
To study the fate of volatile fatty acids (VFA) in the large bowel, we compared the rate of oxidation of 13C-labeled VFA administered rectally with that of the orally administered substrate. On two different days, 1-[13C]acetate was administered rectally or orally to five infants recovering from diarrhea. Breath samples were collected over 4 h and analyzed for 13C enrichment of breath CO2 by gas isotope ratio mass spectrometry. The percent dose recoveries of 13C in breath were fitted to multicompartmental models using the SAAM-27 program. Following model development procedures, the oral acetate breath test curves could be accounted for only by a compartmental model in which labeled acetate underwent absorption into and mixed with a systemic pool before oxidation took place. The rectal acetate breath test curves could be accounted for by a simpler model in which oxidation occurred directly in the compartment in which the rectal acetate was administered, and required no rate-limiting absorptive process. Our results indicate that the labeled acetate was oxidized more rapidly when the substrate was administered rectally than orally. This observation points to the direct utilization of volatile fatty acids within the colon.