Summary. The movement of radio-opaque medium in the vas deferens of rabbits during sexual rest, after sexual stimulation, and after ejaculation, was followed. Bilateral injections of 20 μl Ethiodol were given at the vas–epididymal junction in the urethral direction. Serial radiographs revealed proximal transport of the dye (towards the testis) within 24 h and total containment in the cauda epididymidis within 1–4 days. Subsequently, small amounts of dye moved from the epididymis through the vas and out of the urethra during sexual rest until no dye remained (11 days–8 weeks). Animals with a ligated vas deferens showed no decrease in dye density. Sexual stimulation moved the dye from the epididymis into the vas. The dye was then either rapidly transported proximally during subsequent rest or removed distally if ejaculation followed stimulation. Ejaculation removed some vasal and epididymal dye via the urethra; however, dye left in the vas after ejaculation was rapidly (< 30 min) transported to the proximal duct and then into the epididymis by 24 h. It is concluded that vasal contents are transported in both urethral and testicular directions during sexual rest and that, after stimulation and ejaculation, the rate of proximal transport is increased. This may be indicative of a sperm removal mechanism by the vas deferens which involves the maintenance of an optimal sperm number in the cauda epididymidis at all times.
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