Effect of tubal explants and their secretions on bovine spermatozoa: modulation of ROS production and DNA damage.

Although low levels of reactive oxygen species (ROS) play a physiological role in maintaining sperm function, an increase in ROS generation above these levels may result in the induction of sperm membrane and DNA damage. The main objective of this study was to determine whether bovine oviducal explants (TU) and their conditioned media (CM) have a modulatory effect on the production of ROS, and consequently, on sperm DNA integrity. Thawed sperm were exposed to bovine TU and to CM obtained from the ampullar and isthmal regions after 4 and 12h, and DNA damage and intracellular ROS production was assessed by TUNEL and DHE and SYTOX Green, respectively. Co-incubation of spermatozoa with oviducal explants from the ampullar region (TUa) for 4h resulted in a statistically significant increase in the percentage of spermatozoa with DNA damage compared with controls (P=0.0106), and this increase was positively correlated with ROS levels. Conversely, although the incubation of spermatozoa with explants and conditioned media from the isthmal region (TUi and CMi, respectively) for 12h resulted in an increase of spermatozoa with DNA damage compared with controls (P<0.0001), this increase was not correlated with ROS levels. In conclusion, significant oxidative stress may take place in the oviduct, particularly during short-term incubation, and this may be related to changes in the antioxidant factors present in the oviducal cells and secretions. A redox imbalance in pro-oxidants and antioxidants in the oviduct may lead to oxidative stress and sperm DNA damage.