Uterine epithelial-sperm interaction, endometrial cycle and sperm storage in the terminal zone of the oviducal gland in the placental smoothhound, Mustelus canis.

The fate of spermatozoa deposited within the female reproductive tract has been described in the smoothhound, Mustelus canis. Evidence of uterine epithelial-sperm interaction is presented, as well as documentation of sperm storage specifically in the terminal zone of the oviducal gland. Sperm fate is correlated with morphology of the endometrial cycle and specificity of storage in the oviducal gland. The endometrium of M. canis undergoes dramatic tissue remodeling associated with gestation. In females harboring fertilized ova or preimplantation yolk-reliant embryos, the uterine epithelium is simple cuboidal with mucous droplets for lubrication. The presence of the embryo elicits a response from the uterus, which becomes modified for nutrient and respiratory exchange into vascular uterine attachment sites that abut the distal aspect of the yolk sac. Areas of the uterus adjacent to the uterine attachment sites are termed paraplacental sites. Uterine attachment sites are simple squamous while the paraplacental epithelium is simple columnar. Paraplacental cells have basal metachromatic vesicles and a dense array of apical cytoplasmic filaments. Immediately postpartum the uterine attachment sites, now termed uterine or placental scars, begin to remodel to a mucous epithelium for the next gestational cycle. Paraplacental cells slough off the apical filamentous portion, and sperm become embedded in the epithelium. Bundled sperm occur throughout gestation in the terminal zone of the oviducal gland. Sperm are not embedded in the terminal zone epithelium as in the uterus. Following sperm release from the uterus, the paraplacental epithelium reverts to a mucous epithelium for the next reproductive cycle. Fertilization is presumed to occur in the anterior oviduct above the oviducal gland. The physiological mechanisms that mediate sperm-uterus attachment, release, and storage in the terminal zone of the oviducal gland are currently under investigation.