Reversible inhibition of rabbit sperm-fertilizing ability by cholesterol sulfate.

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 micrograms/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 micrograms/ml significantly (p less than 0.001) decreased fertilization rates to 13.6% (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 less than 0.05) compared to control, Ch, and HChS. In another experiment the use of ChS at 100 micrograms/ml significantly (p less than 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 micrograms ChS/ml, the fertilization rate was 57.7% (23/40), which was not significantly (p less than 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.