Generation of Diacylglycerol during the Acrosome Reaction Induced by Ca²⁺ and Ca²⁺ Ionophore A23187 in Frozen-Thawed Spermatozoa from Fertile and Subfertile Japanese Black Bulls

Abstract

This study investigated the activation of phosphoinositidase C (PIC) and phosphatidylcholine-specific phospholipase C (PLC) during the acrosome reaction of spermatozoa induced by Ca²⁺ and Ca²⁺ ionophore A23187 in a subfertile Japanese black bull. Sperm motility, viability, morphology and penetration of cervical mucus by spermatozoa in a subfertile bull were comparable to those in a fertile bull. When frozen-thawed spermatozoa were stimulated with 3 mM Ca²⁺ and 1 μM A23187, both bulls' spermatozoa showed a time-dependent increase in percent acrosome reactions, but the increase was more rapid and higher in spermatozoa from the fertile bull. The amounts of 1,2-diacylglycerol (DAG) mass, a product of PIC and PLC, peaked at 1 min after a similar treatment with a gradual decline towards 10 min in both bulls' spermatozoa but were significantly higher throughout stimulation for the subfertile bull. These results suggest that active PIC/PLC may be present in spermatozoa of the subfertile bull, and that other mechanisms were possibly associated with the lowered induction of the acrosome reaction. However, it remains unclear whether the high levels of 1,2-DAG mass were responsible.