Removal of sperm-bound seminal plasma components as a prerequisite to induction of the rabbit acrosome reaction

Abstract

When rabbit sperm were pretreated with media of high ionic strength (380 mOsM), which had previously been shown to facilitate removal of sperm-bound seminal plasma components, and subsequently treated with follicular fluid the acrosome reaction was completed rapidly. Treatment of the sperm with follicular fluid alone yielded a greatly decreased rate of acrosome reaction completion, and treatment with the high-ionic strength medium alone caused no visible alteration to the sperm. These results suggest that removal of the sperm-bound seminal plasma components destabilizes the acrosome and prepares it to undergo the acrosome reaction. This destabilization is virtually completed after a 5-minute preincubation of the sperm in high-ionic strength media. Direct comparison of epididymal and ejaculated sperm indicated that epididymal sperm acrosomes were apparently in the same stabilized condition as ejaculated sperm. The effect of the pretreatment by high-ionic strength media could be partially mimicked by pretreatment of sperm with alpha- or beta-amylase or neuraminidase but not by beta-glucuronidase, lipase, pronase, or trypsin. Comparison of the ability of bovine follicular fluid, rabbit follicular fluid, and rabbit serum to induce the rabbit acrosome reaction showed that bovine follicular fluid was 3 to 4 times more effective than rabbit follicular fluid and that rabbit serum was totally ineffective in producing the acrosome reaction. The data support a physiologic role for follicular fluids in the process of fertilization and indicate that removal of sperm-bound seminal plasma components is a prerequisite to efficient induction of the acrosome reaction.