SPERM MOTILITY HYPERACTIVATION FACILITATES PENETRATION OF THE HAMSTERZONA-PELLUCIDA

These experiments were conducted to determine whether or not sperm mot ility hyperactivation facilitates penetration of the zona pellucida of the oocyte. Two approaches were used. For the first, hamster sperm we re incubated for 4.0-4.25 h in a capacitating medium that contained ei ther 2.9 or 25.0 mM sodium bicarbonate. in these media, sperm became e qually capacitated as evidenced by their ability to undergo the acroso me reaction when exposed to lysophosphatidyl choline or intact zonae p ellucidae; however, sperm became hyperactivated only in the medium con taining 25.0 mM bicarbonate. When these sperm were added to cumulus-fr ee oocytes in vitro, only 2 of 88 oocytes were penetrated by sperm pre incubated in 2.9 mM bicarbonate, while 31 of 86 oocytes were penetrate d by sperm in 25.0 mM bicarbonate. It was found that equal numbers of sperm were bound to the oocytes and that equal numbers were acrosome-r eacted on the surface of the zonae in the two media. For the second ap proach, sperm were incubated in a capacitating medium containing 25 mM bicarbonate. When > 70% were hyperactivated, aliquots were added to t hree sets of oocytes. After 10 min had been allowed for sperm to attac h and acrosome-react, inhibitors of hyperactivation were added and the sperm and oocytes were incubated for an additional 20 min before fixa tion and examination for zona penetration. In the dishes treated with the inhibitors verapamil or Cd2+ 1 of 42 and 0 of 42 oocytes were pene trated, respectively, compared with 25 of 40 in controls. Therefore, i t appears that hyperactivation facilitates penetration of the hamster zona pellucida.