Procaine-induced hyperactivation of cryopreserved stallion sperm

It was tested if cryopreserved sperm responded to increasing procaine concentrations in a similar fashion as diluted sperm. Figure 7 shows changes in sperm motility parameters for cryopreserved sperm that was diluted with Tyrode A medium supplemented with increasing concentrations of procaine after thawing. It seems that a higher procaine concentration is required for cryopreserved sperm for attaining a similar increase in curve line velocity as diluted sperm (8 mM instead of 5 mM for a VCL of about 200 µm s^-1).

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4.2.5. Discussion

In the present study is described that procaine can induce hyperactivation, both in capacitating and non-capacitating medium, whereas in vitro capacitation properties are not affected by procaine. Capacitation and hyperactivation are are processes that are often suggested to be linked and dependent on each other since they are both required for fertilization. There are, however, reports that hyperactivation and capacitation can be induced separately, and they involve independent signaling pathways (for review see Suarez, 2008). The results described in this study are in agreement with this. Marquez & Suarez (2004) describe the use of pharmacological agents to induce hyperactivation of uncapacitated bovine sperm.

They, however, found that hyperactivation could not be induced under capacitating conditions that support acrosomal exocytosis. We found that induction of hyperactivation is also possible for cryopreserved sperm, although this requires higher concentrations of procaine

In the current study we found that in vitro capacitation of stallion sperm followed a similar pattern in Tyrode and modified Whittens capacitation medium.

McPartlin et al (2008) reported that modified Whittens medium was most successful in inducing in vitro capacitation in equine spermatozoa. When a procaine-induced hyperactivation was performed in this medium, they obtained 60.7% fertilized oozytes for use in equine IVF (McPartlin et al., 2008, 2009).

Procaine-induced sperm hyperactivation is evident as a star-shaped motility pattern using computer assisted sperm analysis sperm can be classified as hyperactivated objectively. We observed a dose-dependent change in motility

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parameters, with attaining a maximum curve line velocity and lateral head movement with 5mM procaine. Sperm from different stallions, however, exhibited differences in the procaine concentration needed for attaining a similar state of hyperactivation.

Taken together, hyperactivation and capacitation of stallion sperm can be induced under in vitro conditions. It remains to be determined, however, how substances like procaine affect embryo development, and dependent on the outcome of such studies if they can be applied for in vitro fertilization for use in equine reproduction.

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