title: 24-hour secretion patterns of plasma oestradiol 17beta in pony mares in late gestation.
abstract: The mare exhibits nocturnal uterine contractions in the last 6 days of gestation. It is hypothesized that estradiol 17beta (O17beta) may be associated with the nightly increase in uterine contractions. The 24-h secretion pattern of plasma O17beta was measured in 3 pony mares in late gestation to identify changes in release as the mare neared parturition. Blood was collected weekly at 08:00 hours beginning on day 240 and every third day from day 330 until delivery. Serial blood samples were collected from each mare every 30-min for 24-h beginning on gestation day 310 and every sixth day thereafter until parturition. Concentrations of O17beta were elevated at night with lowest concentrations occurring directly before sunset (p < 0.01). The natural log of the variance was increased at sunset (p < 0.01) and was decreased during the 6-h period immediately after sunrise. This pattern was especially evident in the 6 days that preceded parturition. The contrast between nocturnal and daytime concentrations of O17beta in the last 6 days of gestation may contribute to night-time delivery in the mare.
authors.affiliation: Department of Large Animal Clinical Sciences, University of Florida, Gainesville, FL, USA.
authors.forename: L J
authors.initials: LJ
authors.lastname: O'Donnell
authors.forename: B R
authors.initials: BR
authors.lastname: Sheerin
authors.forename: J M
authors.initials: JM
authors.lastname: Hendry
authors.forename: M J
authors.initials: MJ
authors.lastname: Thatcher
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
authors.forename: M M
authors.initials: MM
authors.lastname: LeBlanc
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D004958:Estradiol / Q000097:blood*; D005260:Female; D006736:Horses / Q000097:blood*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000097:blood*; D014590:Uterine Contraction / Q000502:physiology*
chemical_list: D004958:Estradiol