BREAKTHROUGHS IN ANDROLOGY - HYALURONIC-ACID ENHANCES THE ZONA-PELLUCIDA-INDUCED ACROSOME REACTION OF MACAQUE SPERM

Hyaluronic acid (HA) not only surrounds the zona pellucida as part of the cumulus matrix but also is present throughout the zona pellucida a nd the perivitelline space of many mammalian oocytes. However, most in vitro techniques to study sperm-oocyte interaction eliminate HA from the oocyte through enzymatic digestion and/or do not expose sperm to H A prior to zona pellucida binding. This study explores the effect of p reincubation of sperm or oocytes with HA on sperm-zona pellucida bindi ng and subsequent acrosome reaction of bound sperm. Cynomolgus macaque semen was washed, incubated, chemically capacitated with dibutryl cyc lic adenosine monophosphate (dbcAMP) and caffeine, and sperm-zona pell ucida binding assays were performed. In one experiment, sperm were pre treated with HA (100 mu g/ml) during the last 10 minutes of the 30-min ute period for chemical capacitation. In another experiment, only the oocytes were preincubated in the media containing HA. In the third exp eriment, gametes were exposed to HA for 10 minutes after sperm had bee n allowed to bind to zonae pellucida. The preincubation of either sper m or zonae pellucida with HA enhanced the percentage of bound sperm th at were acrosome reacted. However, HA did not affect the number of spe rm bound to zonae pellucida. When sperm already bound to the zona pell ucida were exposed to HA, there was no increase in the percentage of b ound acrosome-reacted sperm. The HA enhancement of the acrosome reacti on of sperm bound to the zona pellucida shown in this study required l ess than 1 minute of sperm exposure to HA-treated zonae during the zon a binding process. However, this enhancement was observed only if the HA exposure preceded sperm-zona binding. This result suggests that HA is interacting with the sperm surface, possibly via a receptor, at the time of initiation of the acrosome reaction. It is unlikely that the effects noted in the current experiments were the result of motility r etention or improvement because the full enhancement of the acrosome r eaction was observed when only the oocytes were pretreated with HA.