Cholesterol-loaded cyclodextrin inhibits premature acrosomal reactions in liquid-stored rabbit spermatozoa.

The effect of pretreatment of rabbit sperm cells with different concentrations of cholesterol-loaded cyclodextrin (CLC) on the occurrence of premature acrosome reactions during 72 h of liquid storage was investigated in three successive experiments. The aim of the first experiment was to establish a liquid storage model to facilitate premature acrosome reactions in rabbit sperm cells and, therefore, examined the relative effects of different dilution rates (1:5, 1:25 or 1:50) and storage temperatures (4°C or 35°C) on the occurrence of premature acrosome reactions. Increasing both dilution rate (from 1:5 to 1:25; P<0.05) and storage temperature (from 4°C to 35°C; P<0.0001) significantly enhanced the percentage of sperm cells that underwent premature acrosome reactions during storage. Therefore, a constant dilution rate of 1:25 and storage temperature of 35°C was employed for the rest of the study. The second experiment examined the effect of different CLC concentrations (0, 0.5, 1.0 and 3.0mg per 120×10(6) spermatozoa) on the occurrence of premature acrosome reactions in sperm cells. CLC supplementation of the extender inhibited (P<0.001) premature acrosome reactions in sperm cells in a dose-dependent manner during 72 h of storage. In the third experiment, the ability of CLC-pretreated sperm cells to undergo acrosome reactions induced by lysophosphatidylcholine (LPC) was evaluated following 72 h of storage. A considerable proportion of sperm cells pretreated with CLC (between 68.7 and 91.8%) underwent the acrosome reaction in response to LPC following 72 h of liquid storage. However, the ability of the sperm cells to undergo the acrosome reaction varied with regards to the dose levels of CLC pretreatment (P<0.001). In conclusion, CLC supplementation prevents premature acrosome reactions in liquid-stored rabbit spermatozoa.