# Comparative Analysis of Fatty Acids Concentration in Liver and Muscle Tissues of Rats and Mice
## 4 Discussion
We suggest that this lipid fraction primarily served as the muscle reservoir for analyzed PUFA and MUFA, the concentrations of which exhibited significant differences among the examined animal groups. Analysis of selected PUFAs in the muscle tissues of mice and rats revealed elevated concentrations of docosahexaenoicenoic acid (DHA; C22:6n3), linoleic acid (LA; 18:2n6), and alfa-linolenic acid (ALA; 18:3n3) in mice. In contrast, the levels of liver UFAs, specifically those derived from NPL sources, were found to be higher in rats than in mice, particularly in the case of LA and ALA.  
PUFAs n-3 are renowned for their ability to alleviate inflammation and provide therapeutic benefits for conditions marked by persistent inflammation and regulate cellular function by modulating signaling pathways and membrane proteins [22; 23]. ALA, EPA (eicosapentaenoic acid), and DHA represent the principal dietary sources of n-3 polyunsaturated fatty acids [24]. ALA is classified as an essential fatty acid due to its inability to be endogenously synthesized, necessitating its acquisition through dietary intake. Our research further demonstrated the tendency to a greater presence of ALA in the muscles of mice as opposed to rats. Given that ALA serves as an exogenous precursor to DHA and EPA, acquired through dietary intake, and considering that all animals in our experiment were maintained on identical diets, the variances observed could potentially be attributed to variations in ALA absorption and distribution levels, which could have contributed to the significantly higher DHA levels recorded in mice. Our findings imply significant variances in fatty acid metabolism between mice and rats muscle and liver, potentially encompassing enzymatic activities such as delta-6 desaturase (D6D), elongase, and delta-5 desaturase (D5D), enzymes which are crucial for omega-3 and omega-6 fatty acids metabolism [25]. The aforementioned hypothesis finds support in our data showing elevated levels of LA in mouse muscles relative to rats. This disparity does not persist at the level of eicosatrienoic acid (DGLA; C20:3n6), a metabolite produced through enzymatic transformations facilitated by D6D and elongase, this may indicate their different activity in both tested animals. While our study did not assess the concentrations of EPA and arachidonic acid (AA), important components in elucidating the interplay between pro-inflammatory and anti-inflammatory factors, our findings align with existing data. They substantiate observations derived from comprehensive lipidome analyses of mice and rats organs, underscoring the discernible dissimilarities among the tested animal cohorts [5]. Likewise, in the case of MUFAs, higher levels of oleic acid (OA; C18:1) were observed in the muscle tissues of mice in comparison to rats. OA is biosynthesized through dietary intake as well as endogenous synthesis. Within the human diet, OA stands as the predominant MUFA [26]. Endogenously, it emerges as the primary monounsaturated omega-9 fatty acid, synthesized predominantly by stearoyl-CoA desaturase 1 (SCD1). This enzymatic process involves the conversion of stearic acid (SA; C18:0) to oleic acid through D9 desaturation catalyzed by SCD1 [27]. The main function of OA is an energy molecule and an element of cell membranes. Moreover, since the identification of membrane receptors for FFAs, new cellular functions have been attributed to it [28]. One of its most characteristic effects is its antioxidant capacity, because it can directly regulate both the synthesis and activities of antioxidant enzymes [29]. Considering that the SA levels in mice and rats maintained on identical dietary regimens remained comparable, disparities observed in OAlevels, similarly to ALA, could potentially stem from variations in SCD1 activity, and/or absorption and distribution levels of both SA and OA.