Diacylglycerol and alkylacylglycerol stimulate ram sperm phospholipase A2

Abstract

• 1.

  1. We have investigated the susceptibility of ram sperm phospholipase A₂ (PLA₂) to stimulation by diacyi- and alkylacylglycerols and by monoacyi- and monoalkylglycerols.

• 2.

  2. PLA₂ activity in sonicates from ram spermatozoa was enhanced when l-stearoyl-2-arachidonoyl-sn-glycerol, the diacylglycerol usually generated by polyphosphoinositide breakdown, was added to a radioactive phosphatidylcholine substrate; the effect was time- and Ca²⁺-dependent.

• 3.

  3. Both diacyi- and alkylacylglycerol considerably enhanced PLA₂ activity; 1-O-hexadecyl-2-O-methyl-rac-glycerol, however, only showed slight stimulatory ability.

• 4.

  4. The monoradylglycerols 1-monohexadecanoyl-rac-glycerol, 2-monohexadecanoylglycerol, and 1-O-hexadecyl-.sn-glycerol had very little effect on the enzyme's activity.

• 5.

  5. Exposure of spermatozoa to 1-oleoyl-2-acetyl-.sn-glycerol (OAG) or 1-O-hexadecyl-2-acetyl-rac-glycerol (1-O-C₁₆/2-C₂), when cells were stimulated with the ionophore A23187 and Ca²⁺, resulted in higher PLA₂ activity in sperm sonicates. Furthermore, parallel experiments showed that exocytosis was enhanced if spermatozoa were treated with A23187/Ca²⁺ and either OAG or 1-O-C₁₆/2-C₂. Since both diacyi- and alkylacylglycerols increased PLAi activity and exocytosis, stimulation of PLA₂ activity by these diglycerides may take place independently from protein kinase C activation.