Relationship between motility and oxygen consumption of sperm from the cauda epididymides of the rat

The oxygen consumption of rat sperm was low (2.7 mu L O-2 10(8) sperm(-1) h (-1)) in caudal epididymal semen (CES) when stimulation of motility was avo ided. The addition of 1 mu L of Krebs Ringer phosphate buffer (KRP) to 40 m u L of CES (CES : KRP = 40 : 1) did not activate motility, but stimulated o xygen consumption 2-fold. Inclusion of 1-5 mM glucose, acetate, pyruvate or lactate in the KRP further stimulated respiration rate (up to 4.3-fold) wi thout activating motility, but respiration was reduced when 2-deoxyglucose replaced energy substrates. Inclusion of dibutyryl cAMP (1 mM) activated sp erm motility in all samples and stimulated oxygen consumption 2.9-fold. Dil ution of CES at the ratio of CES : KRP = 40: 1000 also activated sperm moti lity and stimulated respiration rate 2.9-fold. The combined effect of dibut yryl cAMP and glucose in stimulating respiration was greater than their ind ividual effects. However, the response to cAMP or substrates was not altere d by incubation in KRP containing either 0 or 0.5 mM Ca2+. It was concluded that the motility and metabolism of rat epididymal sperm are suppressed in vivo. Respiration can be stimulated by a small (1.025-fold) dilution and f urther stimulated by the inclusion of energy substrate, without activating motility. However, a larger dilution or inclusion of cAMP activated motilit y and simultaneously stimulated metabolism, with exogenous substrate being required to stimulate respiration to the maximum rate. This suggests that p rior to activation, the rate of oxygen consumption and sperm motility are n ot coupled.