## 4 Discussion  
The presented research aimed to assess if AMTE may exert a protective role on body homeostasis, through vitamin D and NGAL pathways. Our results, as expected, showed the augmented expression of VDR in kidneys of rats subjected to AMTE, in comparison to the sedentary controls. These results may hint an increased release of vitamin D in the circulation after physical activity, confirming findings from literature [43; 44; 45; 46]. [PERSON] et al. demonstrated that indeed intramuscular VDR expression could be effectively promoted by physical activity [47]. Another work suggests that rats performing swimming activity experienced increases in vitamin D level in the serum and, consequently, a greater expression of its receptors in the pancreas, adipose tissue, and muscle [48]. In the present study, the authors did not evaluate the circulating levels of vitamin D in the serum of rats undergoing AMTE protocol; this represents a limitation of the study. Nevertheless, curiously, in our results, the expression of VDR in the heart of active rats did not change significantly when compared to the sedentary controls. A reason for that could be hypothesized by the fact that the circulating vitamin D is converted in its active form in the kidney and, then, determines the increased local expression of its receptor at this level, but does not determine its increase in other organs. Nevertheless, further long-term studies should be done to clarify this aspect. Vitamin D was shown to inhibit the NF-kB pathway [24; 25]. Thus, since the promoter region of NGAL contains a consensus-binding site for NF-kB [58; 59] and VDR was shown to inhibit the activation of NF-kB, it is conceivable that increased levels of circulating vitamin D indirectly inhibit the NGAL expression (Figure 5). In our work, we observed the basal expression of NGAL both in hearts and kidneys of sedentary rats, suggesting that sedentary lifestyle may represent a condition in which it is easier to develop NGAL-involved pathophysiological states. We also assisted to a significant reduction in the detection of NGAL in kidneys inactive rats, as expected, but curiously, not in their hearts. These data suggest that, regarding the crosslink between VDR and NGAL pathways, AMTE did not have any effects on heart tissue, but only on the kidney one. Moreover, a significant and inversely proportional expression of both proteins in kidneys, but not in hearts, of active rats, when compared to the sedentary controls, further confirms the involvement of VDR in the NGAL downregulation. This reasonably happened through the NF-kB inhibition. However, these preliminary findings certainly need further studies to confirm the crosslink between these two pathways. Albeit above reported scientific data highlight that physical activity may increase NGAL levels, they refer to strenuous anaerobic exercise. In our experimental design, we preferred to use AMTE, since this type of exercise is more inclined to induce an adaptive response by the body and our results were different from those reported concerning the strenuous anaerobic exercise. These findings have intriguing clinical implications related to physical activity in humans, emphasizing the beneficial effects of AMTE, but not strenuous exercise, particularly in obese people, given that obesity is associated with inflammation [60]. The limitations of our study refer to the nondosing of NGAL in organic liquids such as urine and blood, which could strengthen immunohistochemical data on tissue; this will lead us to further future studies to deepen the topic of our research.