Increased ovarian follicular angiogenesis and dynamic changes of follicular vascular plexuses induced by equine chorionic gonadotropin in the gilt

Abstract

Follicular angiogenesis and capillary degeneration are crucial ovarian processes in folliculogenesis. The present study was conducted to assess the changes in population of follicular vascular plexuses with different capillary status in prepubertal gilts 72 h after equine chorionic gonadotropin (eCG) (1,250 IU) treatment, using combined vascular corrosion casting and scanning electron microscopy. Follicular fluid concentrations of estradiol, progesterone and vascular endothelial growth factor (VEGF) were determined to confirm the follicular status. Based on the proliferative or degenerative characteristics of their capillaries, follicles were classified into three categories: active angiogenesis, low angiogenesis and degeneration. Irrespective of exogenous gonadotropin treatment in vivo, small follicular vascular plexuses (<4 mm in diameter) exhibited all three conditions in casted ovaries, while medium (4-5 mm) and large (>5 mm) plexuses showed only active angiogenesis or degeneration. eCG treatment significantly increased the population of large, but decreased that of small follicular plexuses. Most large follicular vascular plexuses showed active angiogenesis with higher follicular fluid estradiol: progesterone ratios and VEGF concentration. eCG also increased the percentage of medium follicular plexuses with active angiogenesis. The populations of small follicular plexuses with active angiogenesis were higher in controls, but decreased after eCG treatment. However, treatment of gilts with the gonadotropin increased the percentage of small plexuses (<1.0 mm) with low angiogenesis and those (1-3.9 mm) with extensive capillary degeneration. These findings are consistent with the hypothesis that angiogenesis is involved in selection and growth of small follicles in gilts under the regulation of gonadotropin.

Microvascularization of corpus luteum of bovine treated with equine chorionic gonadotropin

“…These morphological findings were correlated with increased expression of VEGF mRNA and bFGF in luteal tissue of the treated group (Macchiarelli et al, ). The active angiogenesis has also been described by Jiang et al () in vascular molds of pigs’ ovarian follicles treated with eCG. The treatment resulted in an atretic follicle population reduction and increased the amount of VEGF in the follicular fluid, so the angiogenesis is also involved in the selection and follicle growth under the regulation of gonadotropin.…”

“…Other studies have demonstrated that gonadotropin also increased the formation of blood vessels in ovarian follicles of mice (Sato et al, ) and rats (Koos and LeMaire, ). In more recent studies, this eCG angiogenic effect was related to the ability to regulate VEGF expression in granulosa cells, which induced proliferation of endothelial and perivascular cells by a paracrine mechanism, allowing for the formation of new blood vessels in the follicular wall (Barboni et al, ; Jiang et al, ). Moreover, other research that assessed the effects of FSH in vitro buffalo cells showed results of increased expression of VEGF and FGF2 by granulosa cells (Fátima et al, ).…”

Gene injections of vascular endothelial growth factor and growth differentiation factor-9 stimulate ovarian follicular development in immature female rats

“…The structure of the vascular network of cow, rat, and pig follicles is mesh-like (18)(19)(20)(21). Our findings indicated that the ovarian vasculature of the rat was similar to those of pig and cow ovaries.…”

Effect of direct ovarian injection of vascular endothelial growth factor gene fragments on follicular development in immature female rats

“…The preantral follicles have the thecal layer surrounding them (Iijima et al 2006). It has been reported in rabbits (Kanzaki et al 1982, Kitai et al 1985, Kikuta et al 1991, Macchiarelli et al 1993, cows (Yamada et al 1994), and pigs (Jiang et al , 2004) that the single-layered capillary wreath in preantral follicles develops into a multilayered structure in the thickened theca interna layer as the follicles develop into larger and preovulatory follicles. Thus, VEGF gene fragment injection may contribute to the growth of preantral follicles by developing the thecal layer including the blood vessels to supply the nutrients.…”