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Abstract: The result of cryopreservation of semen is crucial for patients in need of fertility preservation.The cryopreservation method is not optimized since only 10 % the sperms are expected tosurvive the treatment. The sperms are exposed to many risk factors such as oxidative stress,osmotic chock and ice crystallization. To minimize the risks, use of cryoprotectants is needed.The use of cryoprotectants helps the cell to dehydrate as penetrating cryoprotectants cancreate space between ice crystals and cell membrane.Two studies were performed. In study one, two different freezing medias (SpermFreezesolution and Cryoprotect II effect on sperm motility after freezing in were compared). Studytwo investigate whether the motility were best preserved if semen froze with all the contentsof the ejaculate or if the sample should be concentrated, with removal of seminal plasma,epithelium cells and dead sperm cells by gradient centrifugation.The project was performed according to recommended instructions for each freezing media.In total, 55 samples were collected for the first study and 23 samples were collected for thesecond study. The sperm motility was measured both before freezing and after thawing.The Cryoprotect II medium preserved the cells better than the SpermFreeze medium(p=0,006). Using SpermFreeze, higher rate of motility was obtained when centrifugation wereperformed before freezing (p=0,033), while this was not observed when using Cryoprotect II(p=0,055). In conclusion Nidacon preserved sperm more effectively than Vitrolife freezemedium. Vitrolife’s freezing medium preserved the samples better if centrifugation wereperformed before freezing. Nidacons freezing medium gave the same result for the samplesno matter centrifugation were performed before or after freezing.

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