Effect of Vitamin E on the Development of Testis in Sheep

Abstract

Vitamin E (VE) is a term that encompasses a group of potent, lipid-soluble, chain-breaking antioxidants. Structural analyses have revealed that molecules having VE antioxidant activity include four tocopherols (┙-, ┚-, ┛-, and ├-tocopherols) and four tocotrienols (┙-, ┚-, ┛-, and ├-tocotrienols). One form, a-tocopherol, is the most abundant form in nature , has the highest biological activity. As a naturally occurring antioxidant, VE is located in biological membranes where it acts to protect the membrane PUFA—polyunsaturated fatty acid (PUFA) from oxidation and attenuate oxidative damage to the cellular membranes (Sugiyama, 1992). Tappel (1962), Burton and Ingold (1986) and Esterbauer et al. (1991) found VE was effective in preventing lipid peroxidation and other radical-driven oxidative events. VE was first isolated from green leafy vegetables by Herbert Evans and Katherine Bishop, two prominent researchers from Berkeley and described as a fertility factor in 1922, then was named tocopherol in 1924 and synthesized in 1938 (Sen et al., 2007). The role of VE in reproductive performance was shown up that supplementing VE increased total sperm output and sperm concentration in boars (Brzezinska-Slebodzinska et al., 1995), rabbits (Yousef et al., 2003) and rams (Luo et al., 2004; Yue et al., 2010). Impairment of mammalian fertility has also been attributed to VE deficiency. The crucial role of VE in animal reproduction has been recognized since 1922 (Evans and Bishop, 1922). To date, there are approximately 100 publications on this topic, which highlight the beneficial effects of this antioxidant on viability, membrane integrity and motility of spermatozoa of different species. The protective effects of VE against oxidative damage of sperm cells become even more significant when hygienic conditions are poorly controlled, as they frequently occur in field. Such conditions are associated with increased incidence of infections/inflammations of reproductive apparatus. During inflammation, the antioxidant defence of reproductive system downplays and generates an oxidative stress (Potts and Pasqualotto, 2003), which may impair testis function and affect negatively semen characteristics (O’Bryan et al., 2000). Because of high content of polyunsaturated membrane lipids, testicular tissue becomes one of the targets for oxidative stress (Mishra and Acharya, 2004). VE supplementation in diet can protect the cell membrane from oxidation and improve the survival rates of cells. Adding VE in diet also increased activity of total anti-oxidation