ABSTRACT
Reactive oxygen species (ROS) are unstable, reactive by-products of oxygen metabolism with the ability to oxidize and modify nearby molecules. Mammalian sperm were the rst cells discovered to produce ROS. Excessive ROS production has been shown to result in reduced sperm motility, increased DNA fragmentation, membrane lipid peroxidation, sperm apoptosis, and a reduction in sperm-oocyte fusion. The perception that ROS is damaging to male gametes was widely accepted until they were discovered to also provide numerous functions vital to the success of fertilization. The key is to keep their levels controlled within certain ranges to allow proper physiological function. Physiological levels of ROS are necessary for the activation of intracellular pathways leading to sperm maturation, capacitation, hyperactivation, acrosome reaction, and chemotactic processes important in sperm-oocyte fusion. This chapter will discuss various physiological roles of ROS and the mechanisms through which it stimulates essential activities of spermatozoa.
