Freeze Preservation of Isolated Populations of Highly Motile Human Spermatozoa

Abstract

Contemporary procedures for the freeze preservation of human and other mammalian spermatozoa involve dilution of the whole semen with a cryoprotective agent alone, such as glycerol, or a semen extender(e.g. glycerol-egg yolk-citrate). After suitable equilibration has occurred, the semen suspension is frozen and stored in liquid nitrogen. Various quantitative protocols have been applied for the rates of cooling of the semen suspension before freezing, and the rates of rewarming during and after thawing. In the human, the great majority of results have indicated that approximately 30%–70% of spermatozoa that were motile prior to freezing regained their motility initially after thawing.^1-11 This range of values seems to be at least as much an indication of the variability of human semen quality as a result of different freeze-thaw protocols. Indeed, human semen of very good quality(high percentage motility, vigorous, progressive sperm swimming) appears to be more resistant to the stresses of freezing and thawing than human semen of less than optimal quality.⁵ This distinction represents a practical limitation of contemporary human semen freeze preservation: It is difficult to anticipate a priovi what the post-thaw motility recovery of a human sample will be.