Poly-implantation and Embryonic Death

Abstract

Embryo implantation in the vizcacha begins at 18 days post-coitum(dpc). It occurs in the caudocranial direction, that is, from the caudal to the cranialuterine segments. For each uterine horn, between 5 and 6 implantation sites (IS) arefound. In each IS, an interstitial and antimesometrial implantation is observed, withan elongated blastocyst due to the growth of the visceral endoderm. Between 26 and70 dpc, the death and resorption of the embryos begins in the cranial and middle IS;on the other hand, the caudal IS keep their growth and development rate, giving riseto two precocial pups after 5 months of gestation. Former studies concluded thatdeath was not due to infectious agents, superfetation, or macro and microscopicvariations in the uterine horns. However, later studies revealed that the uterine hornsare heterogeneous in their anatomy and physiology along their craniocaudal extension.It is proposed that the uterine glands and blood vessels would have a differentialrole between the IS that are resorbed and those that will survive. It was observedthat embryonic death in this species follows a morphological pattern like that registeredin murine rats and mice, considered classic physiological and experimentalmodels. That pattern is characterized by the presence of hemorrhage, neutrophilicinfiltration, necrosis, and fibrosis. Morphological and physiologicalsimilarities observed between related and phylogenetically distant species allow usto propose the vizcacha as an unconventional model for studying spontaneousembryonic death.