Fertilization through spermatozoal microinjection: significance of acrosome reaction.

Acrosome-reacted spermatozoa were microinjected into the perivitelline space of mouse oocytes. After 2 h incubation in culture medium containing lactate and albumin, spermatozoa were transferred into culture medium containing 12 mM of dibutyryl cyclic guanosine 3',5'-monophosphate (dbcGMP) and 10 mM imidazole for 20 min. One motile spermatozoon was injected into the perivitelline space of each oocyte. Fertilization was recognized by the presence of a second polar body and two pronuclei. The overall fertilization rate was 19.6% in the case of dbcGMP-treated spermatozoa as compared to 5.3% for non-treated spermatozoa. Thus, acrosome-reacted motile spermatozoa improve the fertilization rate of sperm microinjection. Sperm microinjection may be a method to foster fertility in cases of oligo-/asthenozoospermia in human in-vitro fertilization.