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Pulmonary intravascular macrophages appear in rats after long-term administration of lipid emulsion and amino acid
J Aksnes1, T J Eide, K Nordstrand
1Cardiothoracic Unit, The National Hospital, University of Oslo, Norway.
Abstract:
Intravascular macrophages have rarely been seen in normal lungs of humans and rats, but in rats endotoxaemia has induced their presence. To study whether substrates used for parenteral nutrition could have a similar stimulatory effect on mononuclear phagocytes, rats were given lipid emulsion (n=5), amino acid solution (n=5), or isotonic saline (n=5) through central venous catheters for 3 weeks. Structural changes in the lung microvessels were evaluated using electron microscopy. The areal fraction of pulmonary intravascular mononuclear phagocytes was 19.6% (SD=8.2) in rats given lipid emulsion (p<0.05) and 8.2% (SD=8.2) in rats given amino acid solution n.s. compared to 2.4% (SD= 4.0) in rats given saline. The increase in areal fraction was mainly due to an increase in cell numbers. In rats given lipid emulsion the intravascular phagocytes were only slightly larger than in rats given saline, but had the morphological features of mature macrophages. The study demonstrates that lipid emulsion recruits pulmonary intravascular macrophages in rats, indicating a stimulatory effect on the mononuclear phagocyte system. The effect was less pronounced with amino acid solution.
Insights
Parenteral nutrition lipid emulsions stimulate the accumulation of pulmonary intravascular macrophages in rats, suggesting an impact on the mononuclear phagocyte system. Amino acid solutions showed a less pronounced effect.
Area of Science:
- Immunology
- Cell Biology
- Histology
Background:
- Intravascular macrophages are rarely observed in normal rat lungs.
- Endotoxemia is known to induce the presence of intravascular macrophages in rats.
Purpose of the Study:
- To investigate the potential stimulatory effect of parenteral nutrition substrates on mononuclear phagocytes.
- To evaluate the impact of lipid emulsion and amino acid solutions on pulmonary intravascular macrophages.
Main Methods:
- Rats received central venous infusions of lipid emulsion, amino acid solution, or saline for 3 weeks.
- Lung microvessel structures were analyzed using electron microscopy.
- The areal fraction of pulmonary intravascular mononuclear phagocytes was quantified.
Main Results:
- Lipid emulsion significantly increased the areal fraction of pulmonary intravascular macrophages (19.6%) compared to saline (2.4%).
- Amino acid solution showed a non-significant increase in intravascular macrophages (8.2%).
- Increased macrophage numbers, not size, accounted for the higher areal fraction in the lipid emulsion group, with mature morphological features.
Conclusions:
- Lipid emulsion administration recruits pulmonary intravascular macrophages in rats.
- Parenteral nutrition lipid emulsions exert a stimulatory effect on the mononuclear phagocyte system.
- Amino acid solutions had a less pronounced effect compared to lipid emulsions.