Scanning electron microscopic and morphometric analysis of the guinea pig uterine luminal surface: cyclic and ovarian...

A morphometric and scanning electron microscopic analysis of endometrial, luminal topographical changes of cyclic and ovariectomized, ovarian steroid-treated guinea pigs was undertaken to determine the effects of cyclic endocrine influences on the uterine surface features recognized to be involved in the process of interstitial blastocyst implantation. Estrogenic stimulation of the uterine epithelial layer induced microvillus growth and closed the endometrial gland openings on the luminal surface. Progestins antagonized these parameters, as indicated by short, sparse microvillus formation over a flat luminal uterine surface on which gland openings were both numerous and prominent. The combined effects of estrogen and progesterone therapies induced luminal epithelial changes resembling those characterizing the cyclic uterine surface at the time of blastocyst implantation. These data indicate that the cyclic alterations in the uterine luminal surface are directly regulated by ovarian steroid hormones, and that these changes in surface structure are synchronized and directly involved in the preparation for blastocyst-uterine interaction during the nidatory process in this species.