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Summary.Acrosin and acrosomal hyaluronidase were inhibited by tetradecyl sodium sulphate (TDSS) in vitroat concentrations of < 10−4M. TDSS prevented the removal in vitroof the cumulus oophorus by testicular hyaluronidase and the zona pellucida by acrosin. TDSS had a contraceptive effect in rabbits when administered intravaginally before coitus or released at levels of 1–3 μg/day from intrauterine silicone rubber devices.

Summary.Introduction of 0·5 mg β-sitosteryl sulphate, a potent acrosin inhibitor, in K-Y jelly into the vagina of rabbits before coitus lowered the pregnancy rate. Cholesteryl sulphate had no effect. A 1·5 × 10 mm silicone rod containing 10% (w/w) β-sitosteryl sulphate released 1–2 μg of compound per day over a 16-day period in vitro. When such implants were placed in rabbit uteri, there was a significant reduction in the numbers of embryos in those horns.

Summary.Four 3 β-hydroxy-Δ5-steroid sulphates were found to be potent and specific inhibitors of the sperm acrosomal proteinase, acrosin. Two of these acrosin inhibitors, desmosteryl sulphate and cholesteryl sulphate, occur naturally in spermatozoa. Desmosteryl sulphate, an inhibitor of the in-vitro capacitation of hamster spermatozoa, has a Kiof 3·5 × 10−6mfor the inhibition of acrosin. The mechanism of inhibition of sperm capacitation by sterol sulphates is probably due to their inhibition of acrosin.