| Selenium has been confirmed to have extensive biological effects, while the studies about the effects of selenium on the prevention and treatment of mastitis are limited at present. This study was designed to build an artificial model of acute mastitis antioxidant damage by the injection of Staphylococcus aureus to teat duts in lactating rats, and then the clinical symptoms, hematological changes, and viscera index were observed, the activity of relevant antioxidant enzymes in breast, liver and serum, and the mRNA expression of relevant antioxidant factors in breast were examined, respectively.140 healthy pregnant Wistar rats with the same age (3 months) and near weight (200g to 250g) were randomly divided into low dose group (0.2 mg/L, n=35), medium dose group (0.4 mg/L, n=35), high dose group (0.4 mg/L, n=35) and control group(0.0 mg/L, n=35). On the 4th day after parturition,0.1ml Staphylococcus aureus suspension (2×107cfu/mL) was injected into each side of the fourth(abdominal) mammary duct. The rats were anaesthetized at Oh,6h,12h,24h,48h,72h and 96 h after injected, then blood, breast, liver, thymus and spleen were collected for determining viscera Index, blood routine, blood biochemistry, activity of relevant antioxidant enzymes in liver, breast and serum, mRNA expression of GPx1, GPx2, GPx3, GPx4, SOD1 and SOD2 in breast. The results are as follows:1. After injected, rats in four groups all showed depression, declined diet, congestion swelling in breast. The number of Gran and WBC, and the activity of AST in blood were significantly increased at first then decreased subsequently in overall, and the peak appeared at 6 to 24h after injection. The statistics of Lymph, ALT (except for the high dose group) and ALP showed the trend of "first decrease then increase to decrease" as a whole, and the valley appeared at 6 to 24h after injection. While the statistics of Mon, RBC, PLT, CREA, BUN, TP, TBIL, DBIL and IDBIL showed no remarkably difference in overall except for some times. In general, selenium supplement could reduce or significantly reduce the thymus index and spleen index as well as the Gran,WBC,PLT, ALT, AST, ALP, TBIL, DBIL and IDBIL(except for some times) (P<0.05), but had no significant effects on the Lymph, Mon, RBC, CREA, BUN and TP(except for some times).6 to 24h after injecting bacteria, the rats from high dose group showed increase or significantly increase in PLT, ALT, CREA and BUN(P<0.05).2. After the injection of Staphylococcus aureus, the statistics of GSH-Px, T-SOD, T-AOC and MDA in liver showed the tendency of first increase then decrease in overall, of which some were significant changed(P<0.05); the statistics of GSH-Px, T-SOD and T-AOC in breast first decreased then increased, while MPO and MDA first increased then decreased, some of them had significant difference(P<0.05); the statistics of T-SOD and T-AOC in serum first decreased then increased overall, while GSH-Px, MPO and MDA first increased then decreased, some of them were significant different(P<0.05). Selenium supplement could make GSH-Px, T-SOD and T-AOC in liver and serum, and GSH-Px in breast increased or significantly increased (P<0.05); and the T-AOC (12h to 48h) and T-SOD (48h to 96h) in breast (P<0.05)significantly decreased; and the MPO in breast increased or significantly increased in overall (except for some times) (P<0.05); but it had no significant effect on MDA in liver, breast and serum (except for some times). The statistics of MDA from high dose group were overall higher than those in other three groups.3. After the injection of Staphylococcus aureus, the mRNA level of GPx1, GPx3, GPx4 and SOD1 in breast significantly decreased (except for some times) (P<0.05), and showed the trend of decrease first then increase subsequently; the mRNA level of GPx2 and SOD2 were overall increased first then decreased, and the peak appeared at 12h to 48h after injection with significant difference (except for the 12h of high dose group)(P<0.05). In general, without the consideration of some times, selenium supplement had no significant effect on the mRNA level of GPx1 and GPx3; increased or significantly increased the mRNA level of GPx2 (12h to 48h) and GPx4 (48 h to 96 h) (P<0.05); decreased or significantly decreased the mRNA level of SOD1 and SOD2(P<0.05).The results suggested that the acute infection of Staphylococcus aureus to breast could induce inflammation and liver damage in rats, which lead to the increase of Gran, WBC and AST in blood. Selenium supplement could improve the antioxidant function of body, the mRNA expression of GPx2 and GPx4 in breast at the latter stage of inflammation, and the activity of GSH-Px in liver, breast and serum, thereby reducing the breast and liver damage, inhibiting body’s inflammation response or development, which finally caused the delay or the drop of the peak in Gran and WBC count, the decrease of PLT, ALT, AST, ALP, TBIL, DBIL and IDBIL in blood. Therefore, the protective function of sodium selenite on the acute mastitis induced by Staphylococcus aureus was mainly achieved by improving the systemic antioxidant activity (liver and blood). In our study, the overall antioxidant effect of medium dose group was better than other two experiment groups. |
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