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In vivo intestinal absorption of manganese in the rat
Abstract:
The mechanisms of intestinal absorption of Mn in rats and the effects of low-molecular-weight ligands in this process were investigated using an in vivo perfusion system. Segments of either jejunum or ileum were perfused with isotonic solutions containing 0.0125 to 0.1 mM MnSO4 X 7H2O, in the presence or absence of double its concentration of either L-histidine (His) or citrate (Cit). In all cases the absorption of Mn declined with time; for example, in the absence of ligand Mn absorption fell from (means +/- SEM) 16.0 +/- 2.2 at 30 minutes to 2.3 +/- 4.1 pmol/(minute X cm) after 90 minutes of perfusion. Comparable declines occurred both in the jejunum and in the ileum in the presence of His or Cit. The initial absorption rates of Mn, obtained by extrapolation, were higher in the jejunum when His or Cit were present than when no ligands were included in the perfusate [means +/- SD, with His, 66.4 +/- 11.9; with Cit, 79.5 +/- 6.2; none = 17.8 +/- 3.3 pmol/(minute X cm)]. In the ileum, optimum absorption with His was observed between pH 7 and 8. The kinetics of in vivo Mn ileal absorption in the presence of His yielded a Kt of 0.056 mM and an estimated Vmax of 158 pmol/(minute X cm). The coefficient of diffusion was calculated to be 1.5 X 10(-3) cm2/minute. These data are compatible with a high affinity, low capacity, active transport mechanism for Mn in the rat intestine and suggest a limited role for small-molecular-weight ligands associated with both diffusional or active translocation processes.
Insights
This study investigated manganese (Mn) intestinal absorption in rats, finding that ligands like L-histidine and citrate enhance Mn uptake. The results suggest an active transport mechanism for Mn absorption in the rat intestine.
Area of Science:
- Gastroenterology
- Nutritional Science
- Physiology
Background:
- Manganese (Mn) is an essential trace element crucial for various physiological processes.
- Understanding the mechanisms of Mn intestinal absorption is vital for addressing potential deficiencies or toxicities.
Purpose of the Study:
- To investigate the in vivo intestinal absorption mechanisms of manganese (Mn) in rats.
- To determine the effects of low-molecular-weight ligands, specifically L-histidine (His) and citrate (Cit), on Mn absorption.
Main Methods:
- Utilized an in vivo perfusion system in rats, perfusing segments of the jejunum and ileum.
- Administered isotonic solutions containing varying concentrations of MnSO4 X 7H2O, with or without L-histidine or citrate.
- Analyzed Mn absorption rates over time and at different pH levels.
Main Results:
- Mn absorption declined over time in both jejunum and ileum, regardless of ligand presence.
- Initial Mn absorption rates were significantly higher in the presence of L-histidine or citrate compared to controls.
- Ileal absorption kinetics in the presence of L-histidine indicated a high-affinity, low-capacity active transport system (Kt = 0.056 mM, Vmax = 158 pmol/(minute X cm)).
Conclusions:
- The rat intestine absorbs Mn via a high-affinity, low-capacity active transport mechanism.
- Low-molecular-weight ligands like L-histidine and citrate can enhance Mn intestinal absorption.
- These ligands may play a role in both diffusional and active Mn translocation processes.