Creatine enhances the duration of sperm capacitation: a novel factor for improving in vitro fertilization with small numbers of sperm

AbstractSTUDY QUESTIONWhy are many sperm required for successful fertilization of oocytesin vitro, even though fertilization occursin vivo when only a few sperm reach the oocyte?SUMMARY ANSWERCreatine produced in the ovary promotes efficient fertilizationin vivo; however,in vitro, creatine is not contained in thein vitro fertilization (IVF) medium.WHAT IS KNOWN ALREADYThe IVF medium enables capacitation of sperm. However, the IVF medium does not fully mimic thein vivo environment during fertilization. Consequently, fertilizationin vitro is more inefficient than in the oviduct.STUDY DESIGN, SIZE, DURATIONFollicular and oviductal fluids were collected and then analyzed for creatine and glucose levels. To determine the physiological functions of creatine, the creatine antagonist 3-guanidinopropionic acid (GPA) was injected into hormonally primed mice. Using conventional IVF protocols, sperm were pre-incubated in IVF medium with creatine and then co-cultured with 10 ovulated cumulus-oocyte complexes (1 –1000 per oocyte) in 50 μl medium droplets.PARTICIPANTS/MATERIALS, SETTING, METHODSGlucose and creatine levels were measured using commercial enzymatic assay kits. The effect of creatinein vivo was assessed by mating experiments using mice treated with or without GPA just before ovulation. To assess the functions of sperm incubated in IVF medium containing creatine, we analyzed (1) the motility of sperm using computer-assisted sperm assay, (2) the capacitation level of sperm by ...
Source: Human Reproduction - Category: Reproduction Medicine Source Type: research