Effects of oxytocin and vasopressin on sperm transport from the cauda epididymis in sheep

Abstract

This study was performed to determine whether oxytocin or vasopressin affect the transport of spermatozoa from the epididymis of rams in vivo. Under general anaesthesia, cannulae were inserted into each ductus deferens and passed into the cauda epididymis of 24 Oxford Down cross rams and the luminal fluid was collected at 10 min intervals for 2-3 h. Animals were divided into seven groups and received either (i) 2 ml 0.9% saline, (ii) 10 micrograms oxytocin, (iii) 100 micrograms oxytocin, (iv) 100 micrograms oxytocin antagonist, (v) 300 micrograms oxytocin antagonist followed by 100 micrograms oxytocin, (vi) 100 micrograms vasopressin, or (vii) 100 micrograms vasopressin followed by 100 micrograms oxytocin, all by i.v. injection. The mass of fluid and number of spermatozoa in each 10 min sample was measured and the motility of the spermatozoa was assessed. Treatment with saline did not affect the mass or the number of spermatozoa in the fluid collected. Oxytocin at 10 micrograms significantly increased both the output of fluid and the number of spermatozoa by twofold. Oxytocin at 100 micrograms produced a greater increase in both fluid output and the number of spermatozoa within 10 min of administration of the peptide. Treatment with oxytocin antagonist had no immediate effect, but subsequently caused a significant reduction in both fluid output and the number of spermatozoa. Pretreatment with oxytocin antagonist inhibited the stimulatory effect of oxytocin. Vasopressin did not increase the number or concentration of spermatozoa in the fluid and appeared to decrease fluid output. No significant changes in the morphology or motility of the spermatozoa collected was observed in any of the samples. These data demonstrate that oxytocin has specific actions on the epididymis to increase sperm transport. They indicate that local oxytocin may be involved in regulating basal contractility of the cauda epididymidis and that augmentation by the peptide in the peripheral circulation, as occurs around the time of ejaculation, may promote a significant increase in the transport of spermatozoa into the vas deferens and ejaculate.

Differential modulation of bovine epididymal activity by oxytocin and noradrenaline

“…The latter finding was unexpected since OT has been generally thought to stimulate epididymal contractility in vivo (Melin 1970, Nicholson et al 1999, Assinder et al 2000 and in vitro (Hib 1974, Filippi et al 2002, Studdard et al 2002. However, these authors primarily investigated the caput and cauda epididymidis.…”

“…Higher doses of AVP have also been shown to stimulate epididymal contractility in rabbits, rams and rats (Kihlstrom & Agmo 1974, Knight 1974, Jaakola & Talo 1981 and increase the seminal volume and sperm content in the ejaculate of the rabbit (Kihlstrom & Agmo 1974). Using lower doses of AVP, Nicholson et al (1999) described a lack of effect in the sheep cauda epididymidis. This is in accordance with the findings in the present study.…”

“…Similar concentrations of AVP and xOT were necessary to induce contraction in the cauda (m), and both peptides administered cumulatively at high doses showed no significant additive effect. Hence, in the cauda (m), VPR seem to be absent and AVP may act through OTR (see also Knight 1974, Nicholson et al 1999.…”

“…It is also well established that oxytocin (OT) is implicated in many male reproductive functions including steroidogenesis and reproductive tract contractility , Thackare et al 2006. OT has been shown to regulate epididymal basal contractility and stimulate sperm release from the epididymal storage at ejaculation in several species (Melin 1970, Hib 1974, Knight 1974, Berndtson & Igboeli 1988, Nicholson et al 1999, Studdard et al 2002, Filippi et al 2003. The circulating level of OT in mammals is in the picomolar range; however, a pulse in systemic OT has been described at ejaculation (Schams et al 1982, Murphy et al 1987.…”

Projections of the posterodorsal preoptic nucleus and the lateral part of the posterodorsal medial amygdala in male gerbils, with emphasis on cells activated with ejaculation

“…Circulating oxytocin increases seminal fluid volume and the number of sperm in the ejaculate of rabbits (Kihlstrom and Melin, 1963) and sheep (Nicholson et al, 1999). It presumably exerts these effects by acting on oxytocin receptors in the epididymis, which have been identified in primates and boars (Ivell et al, 1997).…”