Figure 4: Effect of CNP on the human sperm acrosome reaction by the Coomassie brilliant blue staining method. (a) Data showing the percentage of acrosome-reacted cells at different incubation times under different concentrations of CNP (0, 10−7 and 10−6 mol l−1). (X̄ ± standard deviation, n = 10, *P < 0.05, **P < 0.01, compared with the control group). (b) The acrosome region is stained blue in the acrosome-intact sperm but unstained or stained light purple in the acrosome-reacted sperm, Original magnification ×1000. CNP: C-type natriuretic peptide.