title: Blood vessel remodeling in pig ovarian follicles during the periovulatory period: an immunohistochemistry and SEM-corrosion casting study.
abstract: BACKGROUND
  The present research aims to describe the process of vascular readjustment occurring in pig ovary during the periovulatory phase (from LH surge to ovulation) that drives the transformation of the follicle, a limited blood supplied structure, into the corpus luteum, a highly vascularised endocrine gland required to maintain high levels of progesterone in pregnancy. The swine model was chosen because it is characterized by a long periovulatory window (about 40-44 hrs-similar to human) that permits to recover follicles at a precise endocrinological timing.
  
  
  METHODS
  By validated hormonal protocol (eCG+hCG), able to mimic the physiologic gonadotropin stimulation, preovulatory follicles (PreOFs, 60 h-eCG), follicles in the middle (early periovulatory follicles, EPerOFs, 18 h-hCG) or late (LPerOFs, 36 h-hCG) periovulatory phase were isolated from prepubertal gilts. To understand the angiogenic process, morphological/morphometrical analyses were performed by combining immunohistochemistry (IHC) and SEM of vascular corrosion casts (VCC) techniques.
  
  
  RESULTS
  PreOFs showed a vascular plexus with proliferating endothelial cells (EPI). This plexus was characterized by a dense inner capillary network, with angiogenic figures, connected to the outer network by anastomotic vessels (arterioles and venules of the middle network). EPerOFs decreased their EPI, blood vessel extension in the outer network, and evidenced a reduced compactness of blood vessels. In LPerOFs, a rapid neovascularization was associated to an intensive tissue remodeling: the follicle acquired an undulated aspect presenting arterioles/venules near the basal membrane, increased vascular extension by EPI, sprouting and non-sprouting angiogenesis.The analysis of vascular geometric relations and branching angles evidenced similar values at all stages.
  
  
  CONCLUSIONS
  These data allow us to hypothesize that EPerOFs are in a quiescent status. LPerOFs represent the "metamorphic" follicles that rapidly turn-on angiogenesis to sustain a successful corpus luteum formation. Particularly, it is interesting to underlie that the non-sprouting angiogenesis, typical of structures in rapid neovascularization, occurred only in the LPerOFs. Moreover, vascular geometric relations showed as blood vessel remodeling occurs with the "maximum output and the minimum energetic expense".This knowledge will allow to better understand the mechanisms regulating the reproductive success and to clarify the complex physiological angiogenic process in adult tissues.
authors.affiliation: Department of Comparative Biomedical Sciences, University of Teramo, Piazza A, Moro, 45, 64100 Teramo, Italy. amartelli@unite.it
authors.forename: Alessandra
authors.initials: A
authors.lastname: Martelli
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Palmerini
authors.forename: Valentina
authors.initials: V
authors.lastname: Russo
authors.forename: Carlo
authors.initials: C
authors.lastname: Rinaldi
authors.forename: Nicola
authors.initials: N
authors.lastname: Bernabò
authors.forename: Oriana
authors.initials: O
authors.lastname: Di Giacinto
authors.forename: Paolo
authors.initials: P
authors.lastname: Berardinelli
authors.forename: Stefania Annarita
authors.initials: SA
authors.lastname: Nottola
authors.forename: Guido
authors.initials: G
authors.lastname: Macchiarelli
authors.forename: Barbara
authors.initials: B
authors.lastname: Barboni
mesh_terms: D000199:Actins / Q000032:analysis; D000818:Animals; D016319:Corrosion Casting; D004730:Endothelium, Vascular / Q000166:cytology; D005260:Female; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000032:analysis; D008855:Microscopy, Electron, Scanning; D018919:Neovascularization, Physiologic; D006080:Ovarian Follicle / Q000098:blood supply* / Q000648:ultrastructure; D010060:Ovulation / Q000502:physiology*; D013552:Swine; D014841:von Willebrand Factor / Q000032:analysis
chemical_list: D000199:Actins; D019394:Ki-67 Antigen; D014841:von Willebrand Factor