title: Thyroid hormone supplementation improves bovine embryo development in vitro.
abstract: BACKGROUND
  Early embryo development (EED) forms the basis of assisted reproductive technologies (ARTs), which are used to treat human infertility and to propagate other mammalian species. Thyroid hormones (THs) play an important role in the post-implantation development of the embryo in mammals; however, the effects of THs on pre-attachment embryos are not known. Currently utilized in-vitro embryo production media are devoid of THs and hence our main objective was to examine whether THs affected EED in a bovine model.
  
  
  METHODS
  To determine if THs are present at the site of fertilization and EED in cattle, we evaluated the presence of the hormones in oviductal and uterine horn tissues. To assess the outcome of free TH supplementation (50 ng/ml of each hormone: triiodothyronine-T3 and thyroxin-T4), embryos were followed through standard and TH-supplemented in-vitro procedures, and evaluated for the cleavage rates, blastocyst formation rate and hatching rates. Embryo quality was assessed using TUNEL assay and post-cryopreservation survival was also evaluated.
  
  
  RESULTS
  Although TH levels in in-vitro culture media were found to be approximately 60% of the administered doses, the TH-treated embryos exhibited significant increases in blastocyst formation and hatching rates (P < 0.05). Embryo quality was significantly improved in the treated groups as demonstrated by greater total cell counts and reduced proportions of apoptotic cells (P < 0.05). Finally, TH supplementation was associated with improved post-cryopreservation viability, defined by blastocyst re-expansion and hatching rates after frozen embryos had been thawed and cultured (P < 0.05).
  
  
  CONCLUSIONS
  These findings not only provide a way of optimizing ART efficiency, but also further our understanding of how THs influence embryonic development in mammals.
authors.affiliation: Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada, N1G 2W1.
authors.forename: Fazl A
authors.initials: FA
authors.lastname: Ashkar
authors.forename: Esther
authors.initials: E
authors.lastname: Semple
authors.forename: Chris H
authors.initials: CH
authors.lastname: Schmidt
authors.forename: Elizabeth
authors.initials: E
authors.lastname: St John
authors.forename: Pawel M
authors.initials: PM
authors.lastname: Bartlewski
authors.forename: W A
authors.initials: WA
authors.lastname: King
mesh_terms: D000818:Animals; D001682:Biological Availability; D002417:Cattle; D015925:Cryopreservation / Q000662:veterinary; D046149:Embryo Culture Techniques; D004622:Embryo, Mammalian / Q000187:drug effects*; D047108:Embryonic Development / Q000187:drug effects*; D005260:Female; D011247:Pregnancy; D027724:Reproductive Techniques, Assisted / Q000662:veterinary*; D013963:Thyroid Hormones / Q000494:pharmacology*; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D013974:Thyroxine