Figure 3. NPPC induces sperm accumulation in the capillary.

(a) Effect of NPPC on sperm accumulation in the capillaries at different concentrations. After capacitation, spermatozoa were added to a 150 mL droplet at a final concentration of 1–2 × 10⁶ cells/mL, and capillaries were exposed to various doses of NPPC. The number of spermatozoa in the capillaries was counted after incubation for 20 min. Bars indicate the mean ± SEM of three experiments with three repeats per group in each experiment. *P < 0.05; **P < 0.01. (b) Effect of NPPC on sperm accumulation in the capillaries with ascending and descending gradients. For the ascending gradient, the droplet had no NPPC, and the capillary was supplemented without (−/−) or with 0.1 nM NPPC (−/+). For the descending gradient, the droplet contained 0.1 nM NPPC, and the capillary was supplemented without (+/−) or with 0.1 nM NPPC (+/+). Bars indicate the mean ± SEM of three experiments with two repeats per group in each experiment. *P < 0.05; **P < 0.01. (c) Effect of NPPC on cGMP levels in spermatozoa. Capacitated spermatozoa were incubated without or with 1 nM NPPC for 20 min, and the amounts of cGMP were evaluated using enzyme immunoassay kits. Bars indicate the mean ± SEM of four experiments. **P < 0.01.