Abstract
Differences between the in vitro and in vivo environment in which fertilization occurs seem to play a key role in the low efficiency of porcine in vitro fertilization (IVF). This work proposes an IVF system based on the in vivo oviductal periovulatory environment. The combined use of an IVF medium at the pH found in the oviduct in the periovulatory stage (pHe 8.0), a mixture of oviductal components (cumulus-oocyte complex secretions, follicular fluid and oviductal periovulatory fluid, OFCM) and a device that interposes a physical barrier between gametes (an inverted screw cap of a Falcon tube, S) was compared with the classical system at pHe 7.4, in a 4-well multidish (W) lacking oviduct biological components. The results showed that the new IVF system reduced polyspermy and increased the final efficiency by more than 48%. This higher efficiency seems to be a direct consequence of a reduced sperm motility and lower capacitating status and it could be related to the action of OFCM components over gametes and to the increase in the sperm intracellular pH (pHi) caused by the higher pHe used. In conclusion, a medium at pH 8.0 supplemented with OFCM reduces polyspermy and improves porcine IVF output.
Highlights
Differences between the in vitro and in vivo environment in which fertilization occurs seem to play a key role in the low efficiency of porcine in vitro fertilization (IVF)
During fertilization the environment in which gamete interaction takes place has a pH close to 8.02,21 but this encounter of gametes does not occur by a random process: rather, the spermatozoa must be guided towards the oocyte by different mechanisms[12] through the tortuous path that is the isthmus
Monospermy and efficiency rates increased in the presence of OFCM, reaching the highest percentages at pHe 8.0 with the S device
Summary
Differences between the in vitro and in vivo environment in which fertilization occurs seem to play a key role in the low efficiency of porcine in vitro fertilization (IVF). Unlike other species, the efficiency of in vitro embryo production is very low because of the high incidence of polyspermy that occurs during in vitro fertilization (IVF)[1]. Such polyspermic fertilization might be related with the high number of spermatozoa required to attain an acceptable penetration rate compared with the number that reaches the oviduct in vivo. It has been shown that a reduction in [H+]i and an increase www.nature.com/scientificreports/
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