Cyclical changes in epithelial cells of the vaginal cul-de-sac of brushtail possums (Trichosurus vulpecula)

The aim of this study was to describe and quantify the changes that occur i n cul-de-sac tissue, in particular to epithelial cells and their constituen ts, at specific stages of the estrous cycle in the brushtail possum. Stereological techniques were used to quantify changes in cul-de-sac epithe lial cells collected at four stages of the estrous cycle; the time of remov al of pouch young (RPY; n = 5), of initial follicle development (n = 5), of preovulatory follicle formation (n = 5), of midluteal stage (n = 4), and a gain at RPY(n = 5) after completion of the experiment to examine for any ef fects due to season or time. Tissue was weighed and processed for light mic roscopy, transmission electron microscopy, and stereological analysis. Cul-de-sac epithelial cell volume increased approximately 17-fold at the ti me of preovulatory follicle formation compared with that at the time of RPY , before declining (approximately four-fold greater than at RPY) during the midluteal phase. Epithelial cell volume enlargement was correlated strongl y with the size of the preovulatory follicle present, and maximum size was coincidental with the formation of extracellular spaces and projection of c ell processes between lateral cell membranes. Maximum cell volume was assoc iated with an approximate 25-fold and six-fold increase in cytoplasmic and nuclear volume, respectively Enlargement of the epithelial cells coincided with an increase in cytoplasmic organelle numbers, microvilli prominence, a nd accumulation of secretory vesicles. In the possum, the cul-de-sac epithelial cell undergoes phenomenal remodell ing during the estrous cycle to accommodate an approximate 17-fold increase in volume. This increase in cell volume is coincident with morphological c hanges characteristic of secretory activity and appears to be under estroge n regulation. Anat Rec 254:307-321, 1999. (C) 1999 Wiley-Liss, Inc.