Changes in the Vasculature of Bovine Corpus Luteum During the Estrous Cycle and Prostaglandin F2α-induced Luteolysis

Abstract

Abstract.To investigate the possible role of the vasculature in the local regulation of corpus luteum (CL) function, we determined the densities of capillaries and large blood vessels in the center of the bovine CL during the estrous cycle and following prostaglandin (PG) F2α-induced luteolysis. The CLs at the early (Days 2-3 post-ovulation), developing (Days 5-7), mid , late and regressed (Days 19-21) stages were collected. In addition, the CLs were collected by transvaginal ovariectomy from 12 cows (Day 10 after ovulation), i.e., non-treated (n=3, 0 h, control), at 0.5 (n=3), 2 (n=3) and 12 h (n=3) after injection of a luteolytic dose of PGF2α. Immunohistochemical staining with von Willebrand Factor (specific for endothelial cells that are found in both types of blood vessels) revealed that the density of the luteal blood vessels was significantly higher at the developing and late luteal stages (P<0.05) than at the other stages, whereas the number of larger blood vessels (those stained with α-smooth muscle actin) was higher at the late and regressed luteal stages (P<0.05) than at the other stages. Furthermore, both the density of blood vessels and the number of blood vessels with smooth muscle were significantly higher in the CLs obtained at 2 h and 12 h after PGF2α administration (P<0.05) than in those without PGF2α treatment. These results suggest that the number of blood vessels with smooth muscle per unit area in the regressing CL increased as a result of losing steroidogenic cells and capillaries. The overall results demonstrate that the capillaries disappeared earlier than the large blood vessels during structural luteolysis and suggest that the loss of capillaries in the CL results in a reduced supply of nutrients and oxygen to luteal cells followed by cell death. . It reaches structural and functional maturity by the mid-luteal phase and then begins to regress after Day 17 post-ovulation of the nonfertile cycle. Luteal regression in cows is known to be induced by uterine prostaglandin (PG) F2α until the CL is completely degraded. In cows, luteal regression is characterized by a reduction in P4 production (functional luteolysis) and tissue degeneration by apoptosis (structural luteolysis) [2,3].The development of the bovine CL is known to be associated with an intensive angiogenic process. The intensity of this angiogenic process in the developing CL is similar to the intensities of angiogenesis in the fastest growing tumors [4], and this results in the mature CL becoming one of the most highly vascularized organs in the body [5][6][7] and vascular endothelial cells accounting for up to 50% of the total cells of the mid CL [8,9]. Furthermore, luteal endothelial cells have been known to secrete some vasoactive substances that directly regulate P4 secretion within the CL [10][11][12]. Therefore, in order to know the mechanisms regulating the function of the bovine CL, it is important to investigate the changes in the luteal vasculature.Recently, capillaries and a few blood vessels with smooth muscle were...

Possible action of vasohibin-1 as an inhibitor in the regulation of vascularization of the bovine corpus luteum

“…This Vasohibin-1 in bovine corpus luteum finding is supported by previous studies in which the expression of VEGFA was acutely inhibited and redundant vascular system gradually disrupted during luteolysis in cows (Neuvians et al 2004, Hojo et al 2009, Berisha et al 2010. On the other hand, it is well known that acceleration of luteolysis mobilizes macrophages into the luteal tissue via monocyte chemoattractant protein-1 (MCP1) expression (Penny 2000, Cavicchio et al 2002.…”

“…If pregnancy is not successfully established, the CL is functional for only 17-18 days and must then regress within a few days to allow for the next cycle of ovulation (McCracken et al 1981). In the cow, luteal regression is induced by uterine prostaglandin (PG) F 2a together with disruption of the vascular system, including blood and lymphatic vessels (Niswender et al 1976, Acosta et al 2002, Hojo et al 2009. Vascular systems and endothelial cells within the CL thus have essential roles in luteal function.…”

Lymphatic Involvement in the Disappearance of Steroidogenic Cells from the Corpus Luteum during Luteolysis

“…In the regressing CL, the microvasculature disappears, but the arterioles with smooth muscle remain [23]. Similarly, the large lymphatic vessels with smooth muscle remain within the regressing CL after the lymphatic capillaries disappear [8].…”

Expression of matrix metalloproteinases in bovine luteal cells induced by prostaglandin F2α, interferon γ and tumor necrosis factor α

“…Endothelial cells in the ovine CL detach from the ECM [ 41 ] and undergo apoptosis during luteolysis [ 42 ]. In cattle, capillaries in the CL have been reported to disappear during luteolysis [ 43 ]. It is possible that MMPs induce apoptosis of bovine capillary cells by degrading the ECM.…”