## 4 Discussion
In this study, rats undergoing renal ischemia exhibited severe structural alterations of the kidney including severe tubular dilation, epithelial desquamation, cast formation and tubulointerstitial fibrosis. In rats exposed to SP before renal I/R, most of the abnormal renal histological features were alleviated, but there were still some signs of damage like dilation and tubulointerstitial fibrosis. However, NESP treatment in rats subjected to renal I/R blocked all the severe alterations in kidney histology and restored normal renal histology similar to control rats. Previous studies have shown that inflammatory cytokines such as TNF-\(\alpha\) and IL-1\(\beta\) increase in the renal ischemic model [48; 49]. The increase in these inflammatory cytokines is due to hypoxia followed by decreased renal blood flow. Elevated levels of inflammatory cytokines lead to increased infiltration of inflammatory cells into damaged tissue [14]. In this study, we also found infiltration of inflammatory cells into the renal tissue in the I/R group. Treatment with SP significantly reduced infiltration of inflammatory cells into the kidneys of I/R rats. However, we observed more protection against infiltration of inflammatory cells with NESP treatment. Furthermore, renal ischemia induces hypoxia followed by decreased renal blood, which leads to ROS production and finally tubular cell injury and histological damage. Tissue damage such as tubular dilatation and tubular epithelial cell shedding were also observed in the present study in the I/R group. It is well known that histological damage is associated with MDA content as a marker of ROS generation [14]. Administration of NESP showed important advantages over SP in correcting oxidant/antioxidant imbalance induced by I/R exposure in rats. In this regard, NESP administration in I/R rats induced a greater decrease in MDA and increment in GSH, SOD and CAT compared to the SP-treated I/R rat. In agreement with our finding, [PERSON] et al. demonstrated that the expression of antioxidant enzymes such as SOD and glutathione peroxidase at mRNA level was increased after SP administration in ischemic kidneys [14]. It has been reported that aldosterone can induce ROS generation in cultured mesangial cells [49]; therefore, it seems that the beneficial effects of SP and NESP on correcting oxidant/antioxidant imbalance in this study are partly due to the mineralocorticoid antagonism effect of SP and resultant reduction of renal ROS generation. It should be noted that the better effectiveness of NESP compared to SP treatment over the same period (two days before ischemia) might be due to its better availability. In fact, SP has poor availability due to low aqueous solubility. In order enhance SP bioavailability, different methods have been used including simultaneous administration of surface active agents, micromization of SP [50], complexation of SP with cyclodextrin [51; 52] and utilization of microsomal carriers [23]. Indeed, it was demonstrated that drug delivery via liposomal carrier enhances the bioavailability of drugs, therefore improving longevity, target-ability, distribution characteristics and therapeutic efficacy [19]. Long-term administration of SP in clinic is associated with several side effects such as gynecomasia, menstrual irregularities and decrease in libido due to nonselective progesterone receptor agonistic and androgen receptor antagonistic activity of SP [23]. Therefore, enhancement of the bioavailability of SP with microsomal encapsulation could be a useful therapeutic strategy in patients for reducing dose and period of drug administration and, therefore, decreasing these undesired side effects. However, we should notice that we administered NESP for two days in the present study; therefore, in order to better profile SP side effects in the long-term use such as gynecomastia, a full characterization of biochemical and pathological alterations especially in mammary glands is warranted in future works.