Abstract: 　Objective To determine the role of sodium nitroprusside (SNP) in regulating DNA synthesis of Toxoplasma gondii tachyzoites. Methods Hypodiploid peak of tachyzoite DNA induced by SNP was assessed according to DNA fragmentation. The effect of SNP on appearance of hypodiploid peak and the effect of Ca 2+ on the growth of tachyzoites were evaluated. The intracellular Ca 2+ chelator (BAPTA/AM), antagonist of Ca 2+ channel(verapamil) and the extracellular Ca 2+ chelator (EGTA) were used. The change of DNA content was measured by flow cytometry. Results SNP inhibited DNA synthesis of tachyzoites in a dose and time dependent pattern. The antiproliferative effect of SNP on tachyzoites was inhibited by verapamil, EGTA and BAPTA/AM. The inhibition of the growth of tachyzoites by SNP was associated with increased subploid peak through a Ca 2+ dependent mechanism. Conclusion SNP induced a hypodiploid peak in tachyzoites by altering the Ca 2+ concentration in the plasma of tachyzoite, resulting in damages of the parasite.

Key words: Toxoplasma gondii, tachyzoite, sodium nitroprusside (SNP), nitric oxide, DNA content, flow cytometry