Effects of Toxoplasma gondii Infection on the Level of Serum Nitric Oxide of Rats and Mice

Objective To explore the effect of Toxoplasma gondii infection on the level of serum nitric oxide (NO) of rats and mice. Methods Spraque-Group of six Dawley female rats were divided into six groups. Group Ⅰ: normal control. Group Ⅱ: T.gondii infected. Group Ⅲ: subcutaneous injection with dexamethasone 2 mg/kg, every two days for two weeks, then stop. Group Ⅳ: subcutaneous injection with dexamethasone 2 mg/kg, every two days for two weeks, then infected with T.gondii tachyzoite and stop dexamethasone injection. Group V: subcutaneous injection with dexamethasone 2 mg/kg, every two days during the experiment. Group Ⅵ: subcutaneous injection with dexamethone 2 mg/kg, every two days for two weeks, then infected with T.gondii tachyzoite and continued dexamethone injection. Sera were collected at weekly interval. Rats were killed at sixth week, and sera were collected. Infected rat brains were homogenized and inoculated into the abdominal cavity of mice. Specific SAG1 gene of toxoplasma in these brains was also amplified by PCR. Thirty-six Kunming mice were inoculated intraperitoneally with T.gondii RH strain. Mice were killed at 0, 1, 2, 3, 4, and 5 days post-infection and their sera were collected. The concentration of serum NO was determined by method of nitrate reductase. Results Concentration of serum NO in normal rat serum was (29.30±2.77)?滋mol/L. Two weeks after treatment with dexamethasone, the concentration of serum NO in rats of group Ⅲ, Ⅳ, Ⅴand Ⅵ were (13.24±2.30), (13.33±2.41), (14.98±1.71), and (14.55±2.99) ?滋mol/L, respectively. The level of serum NO in group Ⅱ was increased to (76.79±6.93) ?滋mol/L at the 3rd week after infection with T.gondii, and decreased to (52.34±4.50) ?滋mol/L at the 6th week. The level of serum NO in group Ⅲ was increased to (26.32±2.93) ?滋mol/L at the 4th week, and the concentration was maintained at the normal level. In group IV, the concentration of serum NO was increased to (36.19±7.42) ?滋mol/L at the 3rd week, and reached the peak of (63.60±16.32) ?滋mol/L at the 5th week. The level of NO was then declined. In group V, serum NO was maintained at a low level (13.96～14.98) ?滋mol/L. The level of serum NO in group Ⅵ of rat was found to increase steadily to (58.89±21.70) ?滋mol/L, and the level was then declined. The SAG1 fragment was amplified from the brains of one rat in group Ⅳ and two rats in group Ⅵ. In addition, tachizoite was found in the abdominal fluid of the mice inoculated by the brain of two rats in group Ⅵ. Interestingly, the level of serum NO in these rats were remained low during the experiment. In mice, the concentration of serum NO was (27.47±4.41) ?滋mol/L before infection with T.gondii tachyzoite and decreased to (19.29±3.07) ?滋mol/L 24 hours post infection. Then serum NO increased rapidly and reached to a maximum value of (114.51±8.19)?滋mol/L at day-5 post infection. Conclusion In rat, the concentration of serum NO can be reduced by dexamethasone. Infection with T.gondii resulted in an increase in serum NO. In T.gondii infected mice, a transient reduction of serum NO was seen in the first day after infection. However, the subsequently increase in NO failed to prevent mice from the lethal infection.