Physiological Role of ROS in Sperm Function

Oxygen, in its diatomic form, is essentially reduced to sustain cellular respiration and survival. This reduction leads to generation of highly reactive oxygen metabolites or reactive oxygen species (ROS), which influence various cellular functions. Endogenous ROS generation in male reproductive tissue and its seminal concentration possess both physiological and pathological significance. Seminal fluid contains several cells including immature germ cells, macrophages, and leukocytes, which may generate ROS to varying concentrations. At normal physiological levels, ROS are crucial for vital reproductive functions such as spermatogenesis, to sustain sperm viability and to mediate maturation, hyperactivation and capacitation, and sperm motility as well as acrosome reaction (AR). Excess ROS are quenched by orchestrated actions of antioxidants. However, when the balance between ROS generation and antioxidant capacity is disrupted in favor of the oxidants, an uncontrolled generation of ROS causes oxidative stress (OS) that adversely affects sperm morphology and functions through lipid peroxidation, DNA fragmentation, and apoptosis. This chapter emphasizes upon the endogenous generation of ROS in the male reproductive tract and their physiological roles in mediating sperm functions.