Stress is associated with detrimental effects on male reproductive function. It is known that stress increases reactive oxygen species (ROS) generation in the male reproductive tract. High ROS levels may be linked to low sperm quality and male infertility. However, it is still not clear if ROS are generated by stress in the testis. The objective of this study was to characterize the role of oxidative stress induced by cold-water immersion stress in the testis of adult male rats and its relation with alterations in cauda epididymal sperm. Adult male rats were exposed to acute stress or chronic stress by cold-water immersion. Rats were sacrificed at 0, 6, 12, and 24 hours immediately following acute stress exposure, and after 20, 40, and 50 days of chronic stress. ROS production increased only at 6 hours post-stress, while the activity and expression of antioxidant enzymes, lipid peroxidation (LPO), and sperm parameters were not modified in the testis. Corticosterone increased immediately after acute stress, whereas testosterone was not modified. After chronic stress, testicular absolute weight decreased; in addition, ROS production and LPO increased at 20, 40, and 50 days. The activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) decreased throughout the duration of chronic stress and the activity of catalase (CAT) decreased at 40 and 50 days, and increased at 20 days. The expression of copper/zinc superoxide dismutase (SOD1) and CAT were not modified, but the expression of phospholipid hydroperoxide glutathione peroxidase (GPx-4) decreased at 20 days. Motility, viability, and sperm count decreased, while abnormal sperm increased with chronic stress. These results suggest that during acute stress there is a redox state regulation in the testis since no deleterious effect was observed. In contrast, equilibrium redox is lost during chronic stress, with low enzyme activity but without modifying their expression. In addition, corticosterone increased while testosterone decreased, this decrease is related to the negative effects seen in sperm.

Testicular apoptosis is activated by stress, but it is not clear which signaling pathway is activated in response to stress. The aim of this study was to investigate whether intrinsic, extrinsic, or both apoptotic signaling pathways are activated by acute and chronic stress. Adult male rats were subjected to cold water immersion-induced stress for 1, 20, 40, and 50 consecutive days. The seminiferous tubules:apoptotic cell ratio was assayed on acute (1 day) and chronic (20, 40, 50 days) stress. Apoptotic markers, including cleaved-caspase 3 and 8, the pro-apoptotic Bax and anti-apoptotic Bcl-2 proteins were also determined after acute and chronic stress induction. Additionally, epididymal sperm quality was evaluated, as well as corticosterone and testosterone levels. An increase in tubule apoptotic cell count percentage after an hour of acute stress and during chronic stress induction was observed. The apoptotic cells rate per tubule increment was only detected one hour after acute stress, but not with chronic stress. Accordingly, there was an increase in Bax, cleaved caspase-8 and caspase-3 pro-apoptotic proteins with a decrease of anti-apoptotic Bcl-2 in both acutely and chronically stressed male testes. In addition, sperm count, viability, as well as total and progressive motility were low in chronically stressed males. Finally, the levels of corticosterone increased whereas testosterone levels decreased in chronically stressed males. Activation of the extrinsic apoptotic pathway was shown by cleaved caspase-8 increase whereas the intrinsic apoptotic pathway activation was determined by the increase of Bax, along with Bcl-2 decrease, making evident a cross-talk between these two pathways with the activation of caspase-3. These results suggest that both acute and chronic stress can potentially activate the intrinsic/extrinsic apoptosis pathways in testes. Chronic stress also reduces the quality of epididymal spermatozoa, possibly due to a decrease in testosterone.