Fusion of prostasomes to human spermatoza stimulates the acrosome reaction

Objective: To determine the effect of the fusion of prostasomes to spermatozoa on the acrosome reaction. Design: In vitro study of human spermatozoa. Setting: Healthy volunteers in an academic research environment. Patient(s): Healthy volunteer men, 25 to 35 years old. Intervention(s): Human semen was fractionated into spermatozoa and prostasomes. Fusion of prostasome to spermatozoa was performed at pH 5.5. Progesterone (1 muM) was added when required. Main Outcome Measure(s): Evaluation of the acrosome reaction by fluorescence microscopy. Result(s): The percentage of spontaneously acrosome-reacted cells was very low unless the Ca2+-ionophore A 23187 was added. The treatment of spermatozoa with 1 muM of progesterone scarcely affected the acrosome reaction; a pretreatment in conditions permitting fusion increased it. The addition of progesterone to prostasome-fused spermatozoa further increased the extent of the acrosome reaction. Conclusion(s): The H+-dependent fusion with prostasomes makes spermatozoa more sensitive to the effect of progesterone on acrosome-reaction induction. (C) 2003 by American Society for Reproductive Medicine.