# Comparative Analysis of Fatty Acids Concentration in Liver and Muscle Tissues of Rats and Mice
## 3 Results  
Comparative Analysis of Fatty Acid Profiles in Skeletal Muscle: Delineating Species-Specific Differences in Polar and Non-Polar Lipid Fractions between Mice and Rats  
Mice exhibit significantly elevated levels of total fatty acids (TFAs) derived from PL fraction of skeletal muscle when compared to rats (Figure 1A, Table 2). This same pattern is observed in the PL fraction of saturated fatty acids (SFAs) in mice in comparison to rats (Figure 1B). However, in the non-polar lipids (NPL) and the combined non-polar and polar lipids (NPL + PL), there was no significant difference in SFAs levels between the two species. The analysis of saturated fatty acid levels (particularly: caproic acid--C6:0,palmitic acid--C16:0, and stearic acid--C18:0) in the muscle tissues of both mice and rats did not show any significant difference (Figure 2A). The levels of unsaturated fatty acids were significantly higher in mice than in rats in all three categories: NPL + PL, NL, and PL (Figure 1C). The same results were observed for MUFA levels (Figure 1D). PUFAs levels were higher for the NPL + PL and NPL lipid fractions, but no difference was observed in the PL fraction (Figure 1E). The ratio of polyunsaturated fatty acids into the total fatty acids (Table 2. PUFA/TFA) was significantly higher in mice muscle comparing to rats. The analysis of unsaturated fatty acid levels (particularly: palmitoleic acid--C16:1, oleic acid--C18:1n9c, linoleic acid--C18:2n6c, cis-4,7,10,13,16,19-docosahexaenoicenoic acid--C22:6n3) in the muscle tissue samples of both mice and rats showed that mice had generally higher levels of these unsaturated FAs compared to rats (Figure 2B). The concentrations of 19 fatty acids from mice and rats skeletal muscle samples selected for statistical analysis are presented on the heatmap (Figure 2C). Comparative Analysis of Fatty Acid Profiles in Liver: Delineating Species-Specific Differences in Polar and Non-Polar Lipid Fractions between Mice and Rats  
For Total FA, the NPL + PL, NPL, and PL lipids fractions did not show statistically significant differences between mice and rats (Figure 3A, Table 3). The NPL lipid fraction levels of Saturated FA were significantly higher in rats' liver tissue compared to mice (Figure 3B). Comparison of the selected saturated FA (myristic acid--C14:0, palmitic acid--C16:0, stearic acid--C18:0, tricosanoic acid--C23:0) in the liver of mice and rats revealed statistically higher levels of C14:0, C18:0, and C23:0 in rats liver (Figure 4A). There is a \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Muscle FA** & \multicolumn{2}{c}{**Mice**} & \multicolumn{2}{c}{**Rat**} \\ \hline  & **nmol/mg** & **Q25–Q75** & **nmol/mg** & **Q25–Q75** \\ \hline SFA & 46.2 & 6.6–12.3 & 40.9 & 2.8–4.4 \\ \hline UFA & 38.5 * & 6.7–7.7 & 11.0 * & 0.3–0.2 \\ \hline MUFA & 22.3 * & 2.6–7.8 & 4.1 * & 0.4–0.4 \\ \hline PUFA & 15.3 * & 3.2–2.4 & 6.9 * & 0.5–0.5 \\ \hline NL/PL & 5.1 & 1.5–2.0 & 4.0 & 0.3–0.3 \\ \hline UFA/TFA & 0.46 * & 0.03–0.02 & 0.21 * & 0.02–0.02 \\ \hline PUFA/UFA & 0.39 & 0.04–0.05 & 0.61 & 0.03–0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 2: The comparison of selected fatty acids concentrations from mice and rats skeletal muscle samples. **(A,B)**: All of the values expressed as median interquartile range; * \(p\) \(<\) 0.05, **_p_ \(<\) 0.01. Multiple Mann–Whitney test; n = 6 per animal group. **(C)**: Heat map. Fatty acid level expressed as median interquartile range. Caproic Acid (C6:0); Caprylic Acid (C8:0); Undecanoic Acid (C11:0); Lauric Acid (C12:0); Myristic Acid (C14:0); Pentadecenoic Acid (C15:0); Palmitic Acid (C16:0); Palmitoleic Acid (C16:1); Heptadecenoic Acid (C17:0); cis-10-Heptadecenoic Acid (C17:1); Stearic Acid (C18:0); Oleic Acid (C18:1n9c); Linoleic Acid (C18:2n6c); Arachid Acid (C20:0); cis-11-Eicosanoic Acid (C20:1); Linolenic Acid (C18:3n3); cis-8,11,14-Eicosatrienoic Acid (C20:3n6); Tricosanoic Acid (C23:0); cis-4,7,10,13,16,19-Docosahexaenoic Acid (C22:6n3).