Collagen fibrillar network in estrous and hCG-stimulated rabbit uterus: a SEM study after NaOH maceration.

The three-dimensional (3-D) organization of the collagen fibrillar network in rabbit uterus was studied by cell maceration/scanning electron microscopy (SEM) method, both during estrus and after stimulation with 100 I. U. of human chorionic gonadotropin (hCG). The cellular elements of glutaraldehyde-fixed tissue were effectively removed with 2N-NaOH at 25 degrees C for 5-7 days, followed by rinsing in distilled water. Correlative light microscopy (LM) and transmission electron microscopy (TEM) observations were also made in order to better clarify the natural location and distribution of collagen structures in the uterine layers. In estrous and ovulatory rabbits the superficial compartment of the endometrial stroma was composed of diffusely organized individual collagen fibrils and thin bundles of fibrils, forming specific supporting structures around the uterine glands. The deeper stroma showed a more condensed lamellar arrangement, particularly in the central part of the endometrial folds (plicae). Two distinct collagen networks, detected in the circular and longitudinal muscle layers of the myometrium, represented plexuses of anastomosing fine sheaths around the individual smooth muscle cells. A condensation of the fibrillar framework was observed around the large blood vessels between these two layers. Little alteration in uterine fibrillar network could be noticed in ovulatory animals 12 h after stimulation with hCG. Marked changes indicating collagen reorganization occurred in progestational animals 7.5 days after hCG administration. In this case, the collagen fibrillar network of the endometrium showed an irregular pattern consisting of slender elongations surrounding the labyrinthine spaces of the epithelium and corresponding to numerous, extremely attenuated plicae. Such a rearrangement of fibrils is very likely a response to hormonal stimulation of the uterus. To further identify the location of the blood vessels in the uterine collagen skeleton, vascular casts were also prepared. The collagen fibrillar network not only provides a mechanical support for the structural components of the uterus but also creates a favourable milieu for their activities.