Heat stress causes alterations in the biological processes and functions (Hansen 2009).

Heat stress thus alters several aspects of reproductive physiology, such as blood flow and steroidogenesis (Rivera and Hansen 2001), which manifests in fertility alterations. The harmful effect of summer season on semen quality was reported by Marai et al. (2002) who found that a rise in testicular temperature in rabbits leads to reduced spermatogenesis; temporary sterility; decreased sexual desire, ejaculate volume, motility, sperm concentration, and total number of spermatozoa in an ejaculate; and increased sperm abnormalities and dead sperm.

Aging is a developmental process and causes physiological, psychological and social changes in humans (World Health Organization, 2002). These changes affect the functioning of all body systems and health status. In mammals, deterioration in reproductive performance at the end of reproductive season partly results from a decrease in male fertility. Alexaki et al. (1991) resulted that age appeared to influence on spermatozoa, and found gradually decreasing in concentrations as the animals advanced in age.Changes in motility, viability and morphology of spermatozoa have been reported in the latter part of the reproductive period in animals (Wilson, 1995). Aging causes oxidative stress (Liu, 2002) and decreases in levels of antioxidants and antioxidant enzymes in the heart (Somani et al., 1995) and blood (Ji, 1993) and accumulation of oxidative damage to deoxyribonucleic acid (DNA), lipids, and protein (Beckman and Ames 1998). Also, age factor known to affect semen quality of a male. A significant effect of rabbit’s age on its libido, semen volume and pH, and sperm concentration and motility was reported by Minelli et al. (1999). Studies on turkey showed that the age of the toms affected the sperm quality of both fresh and stored semen. Ageing was accompanied by a reduction in the number of spermatozoa in the ejaculate and in semen volume and by a decrease in motility, viability and membrane integrity of spermatozoa.  Consequently, these changes led to a progressive decline in the fertilizing ability of turkey semen and may also affect its preservability during storage (Laffaldano et al., 2007).

Reactive oxygen species (ROS; free radicals) are molecules that contain one or more unpaired electrons and are, consequently, very reactive, particularly with respect to lipids. They are produced at different sites in the mammalian body. In the mitochondria, the production of superoxide is a by-product of the respiratory chain (Balaban et al., 2005). The sources of ROS produced by the sperm, especially the damaged ones, include radicals like hydroxyl ions, superoxide, nitric oxide, peroxyls and others (Makker et al., 2009). A certain, still low, concentration of ROS is necessary for the sperm function like capacitation, hyperactivation, acrosome integrity and sperm–oocyte fusion (Awda et al., 2009), but ROS become detrimental at excessive amounts. In the testes ROS are produced during the normal testicular spermatogenesis and steroidogenesis (Mathur and D’Cruz, 2011).

Sperm function is undisturbed when the levels of ROS and antioxidants are balanced, as this ensures that no significant damage will occur. In the case of metabolic oxidative stress, however, provoked by excessive ROS production or low antioxidant status or both, impaired sperm function may occur (Agarwal et al., 2003; Aitken and Baker, 2006; Makker et al., 2009). In addition, DNA fragmentation in both nuclear and mitochondrial genomes is a consequence of oxidative stress (Agarwal et al., 2003; Aitken and Baker, 2006). The defense mechanism of the sperm consists of three different and interdependent antioxidant protection systems (Makker et al., 2009), which are dietary (external), enzymatic or non-enzymatic (metabolic).Supplying of antioxidants to sperm samples can protect against the damaging effects of ROS on sperm movement and may be of clinical value in assisted conception procedure (Baker et al. 1996). It is known that improvement of semen characteristics quality depends on antioxidant capacity to limit the damaging effects of lipid.

Tomato and tomato products are excellent source of vitamins A, C, and E. They also contain many other bioactive compounds, such as carotenoids (α-, β-, γ-carotene, and lutein), and other carotenes including phytoene and phytoflune. Moreover, tomato and tomato products also contain flavonoids. Many of these nutrients and phytochemicals have antioxidant properties and, in combination with lycopene, may contribute to the protection against peroxidation (Alshatwi et al., 2010).

Castellini et al. (2002) demonstrated that supra-nutritional vitamin E administration to fertile rabbits improves the oxidative stability of the sperm but not motion characteristics and fertilising ability of the sperm, in spite of the higher vitamin E concentrations occurring in the semen. Also, lycopene has been shown to have strong antioxidant activity; it exhibits the highest physical quenching rate constant with singlet oxygen; it induces cell-to-cell communication; and it modulates hormones, immune systems, and other metabolic pathways (Rao and Agarwal, 1999). Phenolic compounds exhibit a wide range of physiological properties, such as anti-allergenic, anti-atherogenic, anti-inflammatory, anti-microbial, antioxidant, antithrombotic, cardioprotective, and vasodilator effects (Balasundram, et al., 2006). Whereas tocopherol and ascorbic acid are recognized as antioxidant vitamins and heat-labile compounds, lycopene and phenolic compounds are more resistant to thermal processing, being the main antioxidants in processed products.

 

المصدر: Lamiaa,F.Asal.(2013).biological role of natural antioxidant for decreasing the damage impact of free radicals under aging and heat stress condition in rabbits.ph.D. thesis. University of Alex., Egypt.

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