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

Abstract

The oxygen consumption of rat sperm was low (2.7 microL O2 10(8) sperm(-1) h(-1)) in caudal epididymal semen (CES) when stimulation of motility was avoided. The addition of 1 microL of Krebs Ringer phosphate buffer (KRP) to 40 microL of CES (CES:KRP = 40:1) did not activate motility, but stimulated oxygen 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) without activating motility, but respiration was reduced when 2-deoxyglucose replaced energy substrates. Inclusion of dibutyryl cAMP (1 mM) activated sperm motility in all samples and stimulated oxygen consumption 2.9-fold. Dilution of CES at the ratio of CES:KRP = 40:1000 also activated sperm motility and stimulated respiration rate 2.9-fold. The combined effect of dibutyryl cAMP and glucose in stimulating respiration was greater than their individual effects. However, the response to cAMP or substrates was not altered 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 further stimulated by the inclusion of energy substrate, without activating motility. However, a larger dilution or inclusion of cAMP activated motility and simultaneously stimulated metabolism, with exogenous substrate being required to stimulate respiration to the maximum rate. This suggests that prior to activation, the rate of oxygen consumption and sperm motility are not coupled.

Motility activation and second messenger signalling in spermatozoa from rat cauda epididymidis

“…The basic tenet of this proposal is that caudal spermatozoa are immobilized by the mechanical constraint imposed by the high viscoelasticity of plasma from the cauda epididymidis, the dilution of which permits motility (Usselman and Cone, 1983). However, the present study and earlier work (Armstrong et al, 1994;Murdoch et al, 1999) has clearly demonstrated that activation of sperm motility can occur in the absence of dilution. Moreover, only plasma from the cauda epididymidis of rats, hamsters and to a much lesser extent guinea pigs, contain immobilin, yet spermatozoa from other species including mice, dogs, elephants and tammar wallabies, are quiescent in situ in the absence of immobilin (Jones, 1973(Jones, , 1978Carr et al, 1985;Clulow et al, 1992;Jones and Murdoch, 1996).…”

“…Samples (1 l) of semen from the cauda epididymidis were also diluted fivefold with epididymal plasma or fluid from the prostatic or seminal vesicles. The second method, adapted from the procedure used by Pholpramool et al (1985), Clulow et al (1992), Armstrong et al (1994) and Murdoch et al (1999), used a volumetric pipette to deliver various chemical reagents in 50 nl of 300 mOsmol sucrose l −1 to 1 l samples of semen from the cauda epididymidis. This dilution (1.05-fold) with the sucrose solution alone was examined in all studies and did not activate sperm motility.…”

“…A minimum of three replicates was carried out when the test reagent did not activate sperm motility. Armstrong et al, 1994;Murdoch et al, 1999). A fivefold dilution with BWW, which consistently achieved motility scores of 9-10, was used as a reference, against which all motility was scored.…”

Why are epididymal tumours so rare?

“…34 This may stem from the epithelial principal cells' expressing high activities of indoleamine-2,3-dioxgenase (IDO) and tryptophan-2,3-dioxgenase (TDO), both of which can incorporate molecular oxygen into their substrates, 35 and from the high number of luminal spermatozoa, which consume oxygen even when concentrated and immotile. 36 Complementing this non-oxidative environment are anti-oxidant enzymes and components removing superoxide radicals and hydrogen peroxide, 37 some of which are reported in the human epididymal proteome. 38,39 These anti-oxidant strategies make excessive oxidative damage to epididymal cell DNA unlikely.…”

Cell signaling in sperm midpiece ensures quiescence and survival in cauda epididymis

“…It has been well established that sperm may spend up to a few weeks in the cauda epididymis without losing viability and motility potential, before being ejaculated (Jones 2004), while the superfluous/defective sperm are eliminated by altered signaling. The nature's robust cell-survival processes ensure prolonged sperm viability and functionality under extreme stressful conditions of cell crowding (Kempinas & Lamano-Carvalho 1988), limited nutrition (Turner 2002), suppressed respiration (Murdoch et al 1999), hyperosmotic environment (Si et al 2009) and continuous oxidative stress (Aitken et al 2012) in the cauda epididymis. However, the molecular processes that maintain sperm viability under such stressful conditions have not been elucidated.…”