Reversible Inhibition of Rabbit Sperm- Fertilizing Ability by Cholesterol Sulfate1

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Abstract
Experiments were carried out to examine the influences of lipid treatments on the fertilizing ability of rabbit spermatozoa. In vitro insemination of tubal oocytes with in vivo-capacitated sperm resulted in fertilization (IVF) of 81% of the oocytes (38/47) and in vitro development to the morula or blastocyst stage of 92% (35/38) of the embryos within 72 to 96 h. Treatment of capacitated sperm with cholesterol (Ch, up to 100 .mu.g/ml) did not reduce the proportion of oocytes fertilized (fertilization rate, 100%, 8/8). Cholesterol-3-sulfate (Chs) at concentrations of 100 and 1,000 .mu.g/ml significantly (p < 0.001) decreased fertilization rates to 1.36% (8/59), and 3.5% (1/29), respectively. Hypercholesterolemic serum (HChs, 1295 mg cholesterol/dl vs. 45 .+-. 18 mg/dl in normal serum), incubated for 2 h with in vivo-capacitated sperm, did not inhibit fertilization. However, a decreasing trend in fertilization was associated with increasing levels of HChS cholesterol. ChS effectively inhibited the fertilizing ability of capacitated sperm (p < 0.05) compared to control, Ch, and HChS. In another experiment the use of ChS at 100 .mu.g/ml significantly (p < 0.05) reduced the fertilization rate from 56.6% (30/53) to 14.3% (7/49). When a phospholipid-enriched serum medium was added to sperm treated with 100 .mu.g ChS/ml, the fertilization rate was 57.7% (23/40), which was not significantly (p < 0.05) different from the fertilization rate of sperm not treated with ChS (56.6%, 30/53). These data suggest that rabbit sperm fertilizing ability can be reversibly inhibited by cholesterol sulfate.