Indirect determination of stallion sperm capacitation based on esterase release from spermatozoa challenged with lysophosphatidylcholine.

: A spectrophotometric assay was developed to measure the amount of esterase released from stallion spermatozoa. This assay was used to determine the percentages of capacitated stallion spermatozoa, determined by the ability of spermatozoa to undergo an acrosome reaction and release esterase in response to a lysophosphatidylcholine challenge, for spermatozoa incubated under conditions to increase intracellular calcium and cAMP. Incubation with 100 nmol calcium ionophore A23187 l(-1) induced 66% of stallion spermatozoa to capacitate after 60 min of incubation at 37 degrees C. Subsequent experiments investigating the effects of compounds that increase intracellular cAMP concentrations, 8-bromo cAMP (8bcAMP) and isobutyl-methylxanthine (IBMX), revealed that A23187 in combination with IBMX capacitated stallion spermatozoa after incubation for 240 min, while the combination of A23187 + 8bcAMP + IBMX capacitated spermatozoa in 40 min at 37 degrees C. Treating spermatozoa with a combination of compounds that increase intracellular calcium (A23187) and cAMP (8bcAMP and IBMX) capacitate stallion spermatozoa and may provide an efficient method to capacitate stallion spermatozoa for in vitro fertilization procedures.