Effects of phospholipase A2, lysophosphatidyl choline, and fatty acid on the acrosome reaction of human spermatozoa.

An in vitro penetration assay employing zona-free hamster eggs was used to study the effects of phospholipase A2, lysophosphatidyl choline, and fatty acid on the acrosome reaction of human spermatozoa. Human spermatozoa were preincubated for 4 hr in modified Biggers, Whitten, and Whittingham's medium (mBWW) containing a specific phospholipase A2 inhibitor, p-bromophenacyl bromide (p-BPB: 1 X 10(-5) - 1 X 10(-3) M), lysophosphatidyl choline (LC: 5-500 micrograms/ml), and arachidonic acid (AA: 5-500 micrograms/ml), prior to the addition of zona-free superovulated hamster eggs. Eggs were examined microscopically 2 or 4 hr later for evidence of swelling or decondensing sperm heads in the cytoplasm. Lysophosphatidyl choline increased penetration rates of spermatozoa from 43.2% (control) to 91.4% (LC: 50 micrograms/ml). Arachidonic acid also increased penetration rates from 51.6% (control) to 87.0% (AA: 5 micrograms/ml) and 80.5% (AA: 50 micrograms/ml). p-BPB decreased penetration rates from 90.6% (1% dimethyl sulfoxide) to 16.0% (1% dimethyl sulfoxide+p-BPB 1 X 10(-4) M). These results suggest that endogenous phospholipase A2 may break membrane phosphatidyl choline into lysophosphatidyl choline and fatty acid, when the acrosome reaction occurs.