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Intestinal absorption of manganese in experimental malnutrition
Abstract:
We investigated possible changes in mechanisms of the intestinal absorption of Mn in rats malnourished with a low protein-low energy diet (M) for 4 weeks against controls fed a complete diet (C) during the same period. The absorption of Mn in the absence or in the presence of two small molecular weight ligands, citrate and L-histidine, was studied by an in vivo procedure. In both M and C rats, jejunal Mn absorption decreased linearly with time and was enhanced by the presence of the low molecular weight ligands. The initial rate of absorption, for Mn alone, was higher in M than in C rats, but it was indistinguishable between both groups in the presence of either citrate or L-histidine. Total Mn absorption, in midperfusion, was greater in M than in C animals with no ligands in the solutions (means +/- SEM, M = 2,969 +/- 923 vs. C = 654 +/- 218 pmol/cm, p less than 0.05). However, in the presence of citrate or L-histidine, the well-nourished rats absorbed more Mn than M rats. Also, water fluxes across the mucosa had a positive correlation with Mn transport when the ligands were present. This solvent drag of the trace element was not operant in the absence of citrate or L-histidine. These data indicate that the jejunal mucosa of M rats absorbs Mn more effectively than C animals, independently from water fluxes and the presence of small molecular weight chelators. These substances do not alter the uptake of Mn in growth-retarded rats, while they enhance the absorption of the trace metal in well-fed animals.
Insights
Malnourished rats show enhanced jejunal manganese (Mn) absorption compared to controls. However, ligands like citrate and L-histidine improve Mn absorption in well-nourished rats but not in malnourished ones.
Area of Science:
- Nutritional Biochemistry
- Gastrointestinal Physiology
Background:
- Dietary deficiencies, particularly low protein-low energy diets, can significantly impact nutrient absorption mechanisms.
- Manganese (Mn) is an essential trace element crucial for various physiological functions, and its absorption is influenced by dietary factors and luminal components.
Purpose of the Study:
- To investigate the effects of malnutrition on the intestinal absorption of manganese (Mn).
- To examine how small molecular weight ligands, specifically citrate and L-histidine, modulate Mn absorption in both malnourished and control rats.
Main Methods:
- An in vivo jejunal perfusion model was employed in rats fed either a low protein-low energy diet (malnourished, M) or a complete diet (control, C) for four weeks.
- Manganese absorption was measured in the absence and presence of citrate and L-histidine, alongside water flux measurements.
Main Results:
- Malnourished rats exhibited a higher initial rate of jejunal Mn absorption compared to controls when Mn was administered alone.
- While ligands enhanced Mn absorption in control rats, they did not significantly alter Mn uptake in malnourished rats.
- Total Mn absorption was significantly greater in malnourished rats than in controls in the absence of ligands, but this difference diminished with ligands present.
Conclusions:
- The jejunal mucosa of malnourished rats demonstrates an intrinsically enhanced capacity for Mn absorption, independent of water flux or the presence of small molecular weight chelators.
- Citrate and L-histidine enhance Mn absorption in well-nourished rats, likely via solvent drag, but do not improve uptake in malnourished animals, suggesting altered absorption pathways.