title: Effect of a prostaglandin F2α analogue on the cyclic corpus luteum during its refractory period in cows.
abstract: BACKGROUND
  The goal of this study was to examine the response of the cyclic corpus luteum of cows to the administration of a prostaglandin F2α analogue (PGF) during the transition of refractoriness to responsiveness by investigating ultrasonographic changes in the corpus luteum and changes in plasma progesterone concentration in cows following the administration of PGF 3 and 5 days after ovulation.
  
  
  RESULTS
  All cows that responded to PGF given on day 5 ovulated on day 9. In the cows that did not respond on day 5, the luteal cross-sectional area stagnated after treatment, whereas the plasma progesterone concentration continued to increase. In the cows that received PGF on day 3 of the oestrous cycle, the luteal cross-sectional area and the plasma progesterone concentration continued to increase.
  
  
  CONCLUSIONS
  The results of this study suggest that the transition of the bovine corpus luteum from refractoriness to responsiveness to PGF occurs during day 5 of the oestrous cycle because in 5 of 8 cows given PGF on day 5, early luteal regression was evident during the examination 24 hours after PGF administration.
authors.affiliation: Clinic for Reproductive Medicine, Vetsuisse-Faculty University of Zurich, Zurich, Switzerland. bwenzinger@vetclinics.uzh.ch
authors.forename: Beatrice
authors.initials: B
authors.lastname: Wenzinger
authors.forename: Ulrich
authors.initials: U
authors.lastname: Bleul
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003338:Corpus Luteum / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000502:physiology*; D030762:Estrous Cycle; D005260:Female; D003341:Luteolysis / Q000187:drug effects / Q000502:physiology; D011374:Progesterone / Q000097:blood / Q000378:metabolism; D011461:Prostaglandins F, Synthetic / Q000008:administration & dosage / Q000494:pharmacology*; D014463:Ultrasonography
chemical_list: D011461:Prostaglandins F, Synthetic; D011374:Progesterone; C049643:luprostenol