Ovarian microvasculature in normal and hCG stimulated rabbits. A study of vascular corrosion casts with particular regard to the interstitium

Abstract: The microvasculature of rabbit ovaries, with special regard to the interstitial-stromal tissue, was studied by scanning electron microscopy (SEM) of vascular corrosion casts. The casting medium (Mercox) was injected in normal animals and in animals in which ovulation was induced by 100 l.U. of human chorionic gonadotropin (hCG) i.v. Vascular baskets of different size and architecture related to follicles in various developmental stages were observed in the ovarian cortex. Small (primary) follicles showed thin and thready capillaries. Larger (secondary and antral) follicles showed a progressive increase in number, size and tortuosity of round-meshed capillaries, related to adaptation of the growing follicle to the approaching ovulation. Capillary sprouts, due to the enhanced angiogenesis of growing follicles, were seen. These aspects were more evident in ovulatory follicles. In addition, numerous resin leakages, due to the increased permeability of the sinusoidal net, were seen in the cavities of ovulatory follicles. Interstitial-stromal tissue capillaries were diffusely distributed in the cortex among the follicular baskets. Their morphology remained unchanged after hCG stimulus. In the periphery of the cortex, the microvascular net showed large (79-90-mu-m) irregularly rounded meshes, with thin, thready capillaries often anastomosed with those of primary follicles. Inner cortex capillaries were thin, thready and arranged in polygonal meshes of 40-70-mu-m. The arrangement and the distribution of the interstitial-stromal capillaries may have some special role during the cyclic activity of the ovary. In particular, they may be directly involved in the initial development of follicles with consequent differentiation of the theca (peripheral capillary net) and in promoting the vascular supply of steroid-secreting cells of stromal origin (inner cortex capillary net).