STUDIES OF LYSOPHOSPHOLIPIDS RELATED TO THE HAMSTER SPERM ACROSOME REACTION IN-VITRO

Phospholipase A2 and lysophospholipids have been implicated in the mam malian sperm acrosome reaction. In this study we further investigated the role of this enzyme and lysophospholipids on the acrosome reaction of hamster spermatozoa. Hamster epididymal spermatozoa were incubated under capacitation and acrosome reaction-inducing conditions. After 3 .0 and 3.5 h, the spermatozoa were treated with different doses of lys ophosphatidylcholine for 12 min. Then the percentage of motility, hype ractivation, and acrosome reaction was evaluated by light microscopy. Lysophosphatidylcholine, 10 mug/ml, was the highest acrosome reaction- inducing dose without an effect on sperm motility. Lysophosphatidylcho line induced the acrosome reaction only when added to spermatozoa capa citated for a minimum of 2 h. This effect was apparent after 1 min of its addition and reached a plateau after 5 min. Lysophosphatidylethano lamine and lysophosphatidylinositol were also effective in inducing th e acrosome reaction. Lysophosphatidylserine did not have any effect on the reaction, but caused an increase in sperm hyperactivation. Sperm treated with the phospholipase A2 inhibitors quinacrine dihydrochlorid e and p-bromophenacyl-bromide showed an inhibition of the spontaneous occurrence of the acrosome reaction. These inhibitors, however, did no t block the acrosome reaction induced by lysophosphatidylcholine. The time course of the lysophosphatidylcholine-induced acrosome reaction w as the same whether control or inhibitor treated spermatozoa were used . These results suggest that the membrane events of the acrosome react ion initiate with the activation of the phospholipase A2, thus produci ng the fusogen agents necessary for this exocytotic event. (C) 1993 Wi ley-Liss, Inc.