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September 3rd, 2010 | | Make me happy! INTRODUCTION Reactive oxygen species (ROS) include superoxide anion, hydrogen peroxide and derivative hydroxyl radical and hydroxide, and lipid peroxides and derivatives peroxyl radicals (Nappi and Vass, 1998). Under normal circumstances, abundant antioxidant enzymes (e.g., superoxide dismutases and glutathione peroxidases) metabolize these highly reactive derivatives of normal oxidative metabolism. If ROS were not removed in a timely manner by an antioxidant system, an imbalance between free radical generation and removal would lead to oxidative stress. Mammalian cells may encounter oxidative stresses that cause destruction of macromolecules and abnormal function (Jang et al., 2008). The flux of ROS increasing in the vasculature will lead to the initiation and promotion of various human pathological conditions (Loscalzo, 2004; Yang, 2006). Diquat is a moderately toxic chemical that utilizes molecular oxygen to produce superoxide anion radical and subsequently hydrogen peroxide. Diquat does not bind covalently with biological molecules but stimulates cellular production of ROS by undergoing cyclic reduction-oxidation processes (Spalding et al., 1989). The oral half lethal dose (LD50) for diquat in rats is 120 mg/kg. Studies on wild-type mice found that intraperitoneal injection, at one-tenth of LD50, could induce oxidation stress and couldnt kill the animal (Fu et al., 1999). Liang et al. (2007) used the model of diquat (50 mg/kg BW) to study the effect of glutathione peroxidase 4 on against oxidative stress in mice. Our group has established a model for oxidative stress of weaned pigs via administration of diquat at the dose of 12 mg/kg BW. The activities of antioxidant enzymes were decreased for all the diquat-treated pigs (Yuan et al., 2007). Arginine is a basic amino acid and serves as an essential precursor for the synthesis of biologically important molecules such as protein, ornithine, proline, polyamines, creatinine, nitric oxide and agmatine (Wu and Morris, 1998). Although most mammals synthesize arginine (except for cats and ferrets), it is a nutritionally essential amino acid for young mammals and adults during times of stress and illness (Wu et al., 1997). Many researchers have studied arginine transport and metabolism in a wide variety of catabolic states, including sepsis, burn injury, acidosis, and cancer and these studies have shown that arginine transport activity was increased (Pacitti et al., 1992; Inoue and Souba, 1993; Inoue et al., 1994; Rafferty et al., 1994; Pan et al., 2001; Pan et al., 2004). Arginine levels in plasma were markedly reduced in patients with sepsis and pig model of sepsis (Luiking et al., 2004). Thus regulation of arginine homoeostasis, which depends on dietary arginine intake, whole-body protein turnover, arginine synthesis and catabolism, is of considerable nutritional and physiological significance. It is now know that arginine plays important roles in many diverse processes, including vasodilation, diseases and stresses. However, little is known about the alterations of arginine metabolism during oxidative stress in pigs. A better knowledge of these alterations may help in proposing a new nutritional strategy to alleviate such stress. In the present study, we will evaluate the effect of diquat-induced oxidative stress on arginine metabolism in piglets through examining the transporter, enzymes and metabolites of anabolism and catabolism of arginine.
INTRODUCTION Weaning is the most critical stage in pig production. Pigs at weaning are suddenly removed from the sow into a new environment where they have to change from suckling to eating dry feed from a hopper and drinking water from a drinker. Additionally at the same time they are mixed with pigs from other litters and fighting to establish new hierarchies occurs. As a result piglets go through a period of anorexia that compromises the functionality and integrity of the intestinal mucosa (van Beers-Schreurs et al., 1998). Once this period of starvation is over, the hungry piglet eats more feed than its gastrointestinal tract can cope with. The mucosa has lost its integrity and has not yet adapted to producing enzymes for digesting feed of vegetable origin (Miller et al., 1986). All this may increase the amount of undigested feed in the gut and increase the animals susceptibility to pathological disorders. These problems have been traditionally controlled with the use of antibiotics at subtherapeutical doses as growth promoters. However the use of antimicrobial growth promoters has been banned in the European Union due to concerns about the development of antimicrobial resistance that could be transferred to human pathogenic bacteria. However as observed the Danish antibiotic use monitoring programme (DANMAP, 2004), since their ban antimicrobial growth promoters have increasingly been replaced by prescribed therapeutic antibiotics. Veterinary prescription of antibiotics in Denmark has increased continously from 48 tonnes in 1996 to 112.5 tonnes in 2004. In the case of pigs in particular, it increased by 10% between 2003 and 2004. Thus several products, including spray dried animal plasma (SDAP), have been postulated as alternatives. The effect of SDAP on piglet performance has been previously reviewed (Coffey and Cromwell, 2001; van Dijk et al., 2001a). The objective of this paper is to review the evidence available to support the use of spray dried animal plasma as an alternative to antibiotics in weaning pigs. At weaning, the supply of the beneficial factors provided by sows milk to the piglet is suddenly stopped. Among these epidermal growth factor, polyamines, insulin and insulin like growth factor have been reported to contribute to the development of the intestinal tract (Pluske et al., 1997). Sows milk also contains protective antibodies, the main immunoglobulin in milk being IgA (Husband and Bennell, 1980). After the first days of age, the IgA and other milk immunoglobulins are not absorbed at the intestinal level; they provide continuous defence throughout the intestinal lumen against infectious organisms to which the sow is resistant (Svendsen and Larsen, 1977). This protection is essential while the piglets own IgA production has not completely developed; this does not occur until 6-8 weeks of age (Svendsen and Brown, 1973). Therefore piglets weaned at 3-4 weeks of age lose the protection from maternal antibodies and cannot efficiently fight infections. It has been estimated that by 3 to 4 weeks of age the piglet receives approximately 1.6 g of IgA/d (Svendsen and Brown, 1973). Ideally the piglet should be offered sows milk for the first days post-weaning. Unfortunately this is not possible, but an attempt to use ingredients with similar characteristics is feasible. The sows mammary epithelium transforms precursors from blood or interstitial fluid into milk constituents by different processes. Among these transcytosis is of special interest; by this mechanism, intact proteins, immumoglobulins, hormones and growth factors can cross the mammary epithelium and be secreted intact in the milk (Hunziker and Kraehenbuhl, 1998; Monks and Neville, 2004). Many of the components in sows milk may also be present in SDPP, and therefore SDPP may be a good substitute for sows milk.