The blood vascular wreath of rat ovarian follicle, with special reference to its changes in ovulation and luteinization: A scanning electron microscopic study of corrosion casts.

Abstract

Summary. Blood vascular casts of rat ovaries were prepared by injection of a low viscosity methacrylate medium, and observed by scanning electron microscopy. The proper vascular pattern of the rat ovarian follicle starts as a basket-like wreath of fine capillaries around the primary follicle. As the follicle grows larger, the wreath becomes more developed. The fully developed wreath around the Graafian follicle consists of sinusoidal capillaries. In ovulation, the apical area of the wreath is opened and the basal area of the wreath is elevated. After ovulation, the wreath shrinks and its opened area is closed, with markedly dilated vessels directly continuous with the arterial capillaries. The wreath then transforms, by intense new formation of capillaries, into a conglomerated sinusoidal capillary plexus with an avascular area within it. The avascular area soon disappears by continued intense formation of capillaries in the plexus, and a complete and dense vascular network of the corpus luteum is formed. The capillaries of the fully developed corpus luteum are small in caliber and not sinusoidal in nature. Discontinuities of the capillaries and a flattening of the efferent branches are the initial signs of the degeneration of the corpus luteum. The small markedly degenerated corpus luteum contains only scattered thready capillaries. The corpus albicans contains few blood vessels.

The Microvasculature of the Ovary. A Review by SEM of Vascular Corrosion Casts.

“…is similar to the vascular architecture found in corpora lutea of late diestrous rats [31] and notpregnant pigs and monkeys [50]. Small, flat venules were seen forming on the surface of these PPCL through the confluence of several sinusoidal capillaries [36].…”

“…At present, scanning electron microscopy (SEM) of vascular corrosion casts allows the best morphological 3D reconstruction of the vascular supply, including its finest ramifications, in both normal and experimental conditions, as observed in ovary of rodents [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], horses [42], cows [43,44] and sheep [45,46]. This technique allowed significant information on the ovarian cycle, and better clarified the role of vascular morphodynamics in the development of the LFC [37,[47][48][49].…”

“…Half of the samples were frozen at 18 C and cut with a cooled razor blade, to allow the visualization of the internal structures of the casts. All samples were air dried, mounted on aluminum stubs and coated with gold or platinum [31,[34][35]. SEM observations were performed at low accelerating voltage (3-7 kV), in Hitachi FE S-4000 and S2R or Cambridge Stereoscan 150 scanning electron microscopes.…”

“…On the other hand, these follicles showed an individual and well recognizable, although peculiar, vascularization. Presumably they underwent recruitment from the resting primordial pool [31], but were stopped in their further growth and destined to form a reservoir of steroid-synthetic cells for the interstitial gland [35], being in any case active in modulating a districtual control of ovarian activities.…”

“…According to the previous SEM studies on ovarian vascular casts [31,48] and to electron microscopic data on unstimulated rabbit ovaries [2], Types 1 and 2 VP corresponded to the theca microvasculature of growing follicles in the evolutive phase, from primary to preovulatory stages [26-28, 31, 34, 37-49]. This VP, in fact, displayed a gradual increase of the wall thickness, and a development of the inner vascular layer from a polygonal-meshed network of thin capillaries (Type 1 VP) to a rounded-meshed network of thick sinusoids (Type 2 VP).…”