Abstract:

【Abstract】 Objective To observe the effect of nitric oxide （NO） on exflagellation of malaria parasite. Methods The level of parasitemia and gametocytemia in DBA/2 mice infected with Plasmodium yoelii 17XL was measured by scanning Giemsa-stained blood smears, and the NO level in culture supernatant of splenocytes was checked using Griess reaction. The mice were injected with different doses of NO donor （NOC5） on day 4 post-infection, and control mice were injected with NOC5 precursor. On day 6 post-infection, mice were injected with NOS inhibitor （L-NMMA）, and control mice were injected with D-NMMA and PBS, respectively. Blood samples were collected from tail vein of mice before injection, 30 and 60 min after being injected with NOC5 and NOC5 precursor, 4 and 8 h after being injected with L-NMMA, D-NMMA, and PBS respectively. Exflagellation number of gametocytes in blood culture was counted under microscope. Results The NO level in culture supernatant of splenocytes from mice on day 4 and 6 post-infection was 16.5 mmol/L and 30.4 mmol/L， and exflagellation number was 11.33 and 0.66, respectively. The number of exflagellation in parasitized erythrocytes, obtained from mice on day 4 post-infection， was 5.33 and 2.66， respectively， 30 and 60 min after injection of 1 mg NO donor （NOC5）, significantly lower than that of the control （P＜0.01）. The number of exflagellation in parasitized erythrocytes derived from mice on day 6 post-infection was 1.83， 8 h after the injection of NOS inhibitor （L-NMMA）， which was significantly higher than that of the control （P＜0.01）. Conclusion NO is a major effector molecule resulting in natural transmission-blocking of malaria parasite by directly inhibiting exflagellation of male gametocytes.