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

This study was performed to determine whether oxytocin or vasopressin affec t the transport of spermatozoa from the epididymis of rams in vivo. Under g eneral anaesthesia, cannulae were inserted into each ductus deferens and pa ssed 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 in to seven groups and received either (i) 2 mi 0.9% saline, (ii) 10 mu g oxyt ocin, (iii) 100 mu g oxytocin, (iv) 100 mu g oxytocin antagonist, (v) 300 m u g oxytocin antagonist followed by 100 mu g oxytocin, (vi) 100 pg vasopres sin, or (vn) 100 pg vasopressin followed by 100 mu g oxytocin, all by i.v. injection. The mass of fluid and number of spermatozoa in each 10 min sampl e 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 flu id collected. Oxytocin at 10 mu g significantly increased both the output o f fluid and the number of spermatozoa by twofold. Oxytocin at 100 mu g prod uced a greater increase in both fluid output and the number of spermatozoa within 10 min of administration of the peptide. Treatment with oxytocin ant agonist had no immediate effect, but subsequently caused a significant redu ction in both fluid output and the number of spermatozoa. Pretreatment with oxytocin antagonist inhibited the stimulatory effect of oxytocin. Vasopres sin did not increase the number or concentration of spermatozoa in the flui d and appeared to decrease fluid output. No significant changes in the morp hology or motility of the spermatozoa collected was observed in any of the samples. These data demonstrate that oxytocin has specific actions on the e pididymis to increase sperm transport. They indicate that local oxytocin ma y be involved in regulating basal contractility of the cauda epididymidis a nd that augmentation by the peptide in the peripheral circulation, as occur s around the time of ejaculation, may promote a significant increase in the transport of spermatozoa into the vas deferens and ejaculate.