Summary. Ram cauda epididymal spermatozoa were incubated for 10 min at 34°C with or without 1·0 mm-RS-α-chlorohydrin before (1) 5 mm-d-glucose or (2) 10 mm-l-lactate plus 1 mm pyruvate or (3) 5 mm-d-glucose plus 10 mm-l-lactate plus 1 mm-pyruvate or (4) no substrate was added. Without α-chlorohydrin, the motility, the ATP concentration and the energy charge of the spermatozoa were maintained for 240 min by substrate combinations 1–3 but with no added substrate (4) the motility declined after 60 min. All the values decreased dramatically after 10 min in spermatozoa exposed to α-chlorohydrin in substrate conditions 1 and 3 (glucose present) but α-chlorohydrin had no significant effect in conditions 2 and 4 (no glucose) except after prolonged incubation. In a dose—response experiment glucose-dependent ATP dissipation began to occur with 0·025 mm-rs-α-chlorohydrin. A similar effect was seen in boar spermatozoa exposed to 0·1–5·0 mm-α-chlorohydrin and 5 mm-d-glucose. With boar spermatozoa the presence of 10 mm-l-lactate and 1 mm-pyruvate as well as glucose prevented the loss of ATP.
We conclude that this concerted action of α-chlorohydrin and glucose is probably responsible for the contraceptive action of α-chlorohydrin and propose that it may depend on 'futile substrate cycling' in the glycolytic pathway.