title: Mechanisms responsible for increase in circulating inhibin levels at the time of ovulation in mares.
abstract: In female mammals, inhibin is secreted by the granulosa cells and selectively inhibits secretion of FSH. Although circulating immunoreactive (ir)-inhibin levels decrease after ovulation as a result of the disappearance of its main source, they abruptly increase at the time of ovulation in mares. To investigate the mechanisms responsible for this increase, 50 ml of equine follicular fluid (eFF) was administered into the abdominal cavity of mares during the luteal phase (eFF, n = 4). One hour after treatment, plasma levels of ir-inhibin and inhibin pro-alphaC (but not estradiol-17beta) were significantly higher in eFF-treated mares than in control mares (n = 4). The hormone profiles in eFF-treated mares were similar to those in mares with the spontaneous or hCG induced ovulations. The present study demonstrates that the release of follicular fluid into the abdominal cavity when the follicle ruptures is responsible for the ovulatory inhibin surge in the mare. These findings also suggest that circulating inhibin pro-alphaC may be useful for determining the time of ovulation in the mare.
authors.affiliation: Laboratory of Molecular and Cellular Biology, Clinical Science and Pathobiology, Equine Research Institute, Japan Racing Association, Tochigi. ynambo@center.equinst.go.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Nambo
authors.forename: K
authors.initials: K
authors.lastname: Nagaoka
authors.forename: Y
authors.initials: Y
authors.lastname: Tanaka
authors.forename: N
authors.initials: N
authors.lastname: Nagamine
authors.forename: H
authors.initials: H
authors.lastname: Shinbo
authors.forename: S
authors.initials: S
authors.lastname: Nagata
authors.forename: T
authors.initials: T
authors.lastname: Yoshihara
authors.forename: G
authors.initials: G
authors.lastname: Watanabe
authors.forename: N P
authors.initials: NP
authors.lastname: Groome
authors.forename: K
authors.initials: K
authors.lastname: Taya
mesh_terms: D000818:Animals; D006063:Chorionic Gonadotropin / Q000008:administration & dosage; D004958:Estradiol / Q000032:analysis / Q000097:blood; D030762:Estrous Cycle; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry / Q000502:physiology; D006736:Horses / Q000097:blood*; D007265:Inhibins / Q000032:analysis / Q000097:blood*; D007700:Kinetics; D006080:Ovarian Follicle / Q000502:physiology; D010060:Ovulation / Q000502:physiology*; D010062:Ovulation Induction; D011498:Protein Precursors / Q000097:blood
chemical_list: D006063:Chorionic Gonadotropin; D011498:Protein Precursors; C095971:inhibin-alpha subunit precursor; D004958:Estradiol; D007265:Inhibins