Cryopreservation of rabbit semen comparing the effects of different cryoprotectants

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The low survival of sperm after freezing is a major
drawback for the widespread use of frozen semen in artificial
insemination programs for livestock animals such as
the rabbit, in which spermcryopreservation has only been
used for experimental purposes [1]. During cryopreservation,
sperm cells undergo stress such as changes in the
osmotic balance and temperatures during cooling, freezing,and rewarming. These changes lead to ice crystal formation,
which is among the main biophysical factors which
cause sperm death [2]. Cryoprotective agents (CPAs) that
permeate the cell membraneare needed to increase
membrane fluidity and partially dehydrating the cell,
lowering the freezing point, and thus reducing the number
and size of intracellular ice crystals formed. However, theparadox is that CPAs themselves can have a toxic effect on
sperm (membrane destabilization, protein and enzyme
denaturation) and this effect is related directly to the
concentration used and the timeof cell exposure [3]. Added
to the freezing medium, nonpermeating cryoprotective
substances such as proteins, or amino acids and sugars,
acting mainly as osmoprotectants, can mitigate thecryodamage
caused by permeating CPAs. At similar concentrations,
these substances are less toxic than permeable CPAs,
inhibit ice growth and help the sperm to stabilize internal
solute concentrationsunder osmotic stress, and this
reduces the amount of penetrating CPAs needed [3].
According to the freezing rate, sperm cryopreservation
techniques can be divided into two main categories: slowfreezing (conventional freezing) and ultrarapid freezing
(vitrification or similar state to vitrification). Conventional
freezing involves a step-wise reduction in temperature,
but ice crystals that formwithin the cell can have
extremely deleterious effects, such that a balance needs to
be found between the beneficial and toxic effects of
permeating CPAs. Alternatively, vitrification is a...
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