title: Histological analysis of arteriovenous anastomosis-like vessels established in the corpus luteum of cows during luteolysis.
abstract: BACKGROUND
  The mechanisms regulating the function and regression of the corpus luteum (CL) have not yet been elucidated in detail. The regressed CL of cows was previously reported to be filled with unusual vessels like arteriovenous anastomosis (AVA); however how these vessels are being established during luteolysis remains unknown.
  
  
  METHODS
  The bovine CL at different luteal stages and regressing bovine CL induced by prostaglandin F2α(PGF) were histologically analyzed using light and electron microscopic levels. The changes in mRNA expression of genes encoding α-smooth muscle actin (SMA; Acta2) and transforming growth factor β1 (Tgfb1) in luteal tissues were analyzed by quantitative RT-PCR.
  
  
  RESULTS
  AVA-like vessels appeared in the regressed CL with a diameter less than 1.5 cm in which no functional luteal cells and macrophages were observed. Epithelioid cells in the AVA-like vessel wall were immunoreactive for SMA, and the lumen of the vessels were narrow. Immunoreaction for SMA was found in the tunica media of typical arteries and arterioles, and pericytes around capillary vessel. Cells with elongated cytoplasmic processes -resident fibroblasts expressing vimentin- distributed in the CL parenchyma without any association with blood vessels are also immunoreactive for SMA, and accumulated around arteries and arterioles during the late-luteal stage. In the regressed CL, walls of arteries and arterioles consisted of more than two layers of epithelioid cells positive for both SMA and desmin, suggesting that they are myofibroblasts transformed from fibroblasts. The percentage of the area positive for SMA and the mRNA expression of Acta2 were significantly increased in the regressed CL; however, they did not alter when a luteolytic dose of PGF was injected in vivo and collected within 24 h after the injection. On the other hand, Tgfb1, a known regulator for myofibroblast transformation, was significantly increased in PGF-induced regressing CL as well as in the CL during the late-luteal stage.
  
  
  CONCLUSIONS
  SMA-positive myofibroblasts accumulates around the arteries and arterioles to form AVA-like vessels during luteolysis in cows. PGF indirectly regulates myofibroblast transformation through enhancing the expression of TGFβ1. These peculiar AVA-like vessels may be involved in the regulation of blood flow in the bovine CL during luteolysis.
authors.affiliation: Laboratory of Histology and Cytology, Hokkaido University Graduate School of Medicine, Kita 15-Nishi 7, Kita-ku, Sapporo, 060-8638, Japan. niojun@med.hokudai.ac.jp.
authors.forename: Junko
authors.initials: J
authors.lastname: Nio-Kobayashi
authors.affiliation: Laboratory of Histology and Cytology, Hokkaido University Graduate School of Medicine, Kita 15-Nishi 7, Kita-ku, Sapporo, 060-8638, Japan.
authors.forename: Kaya
authors.initials: K
authors.lastname: Miyazaki
authors.affiliation: Laboratory of Reproductive Physiology, Graduate School of Environmental and Life Science, Okayama University, Tsushima Naka Kita-ku 1-1-1, Okayama, 700-8530, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Hashiba
authors.affiliation: Laboratory of Reproductive Physiology, Graduate School of Environmental and Life Science, Okayama University, Tsushima Naka Kita-ku 1-1-1, Okayama, 700-8530, Japan.|Obihiro University of Agriculture and Veterinary Medicine, 2-11, Nishi, Inada-cho, Obihiro, 080-8555, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Okuda
authors.affiliation: Laboratory of Histology and Cytology, Hokkaido University Graduate School of Medicine, Kita 15-Nishi 7, Kita-ku, Sapporo, 060-8638, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Iwanaga
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001163:Arteriovenous Anastomosis / Q000166:cytology* / Q000648:ultrastructure; D015415:Biomarkers; D002417:Cattle; D003338:Corpus Luteum / Q000033:anatomy & histology / Q000098:blood supply* / Q000502:physiology*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D015870:Gene Expression; D007150:Immunohistochemistry; D003341:Luteolysis / Q000502:physiology*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
chemical_list: D000199:Actins; D015415:Biomarkers; D053773:Transforming Growth Factor beta1
keywords: Arteriovenous anastomosis; Luteolysis; Myofibroblasts; PGF2α; TGFβ1