title: Effects of a non-steroidal aromatase inhibitor on ovarian function in cattle.
abstract: Effects of the non-steroidal aromatase inhibitor letrozole on ovarian function in cattle were determined. The hypothesis that letrozole would arrest growth of the dominant follicle, resulting in emergence of a new follicular wave at a predictable post-treatment interval, was tested. Heifers were assigned randomly to four groups 4 days after follicular ablation (~2½ days after wave emergence) and given intravenous doses of 500 (n = 9), 250 (n = 10), or 125 µg kg⁻¹ (n = 10) letrozole or phosphate-buffered saline (controls; n = 10). Blood was collected and ovarian structures were monitored daily by transrectal ultrasonography. Plasma concentrations of LH and FSH were measured by radioimmunoassay; plasma concentrations of letrozole were determined by high-performance liquid chromatography tandem mass spectrometry. A single intravenous dose of letrozole did not induce regression of the dominant follicle present at the time of treatment, nor did it directly affect FSH release. Conversely, treatment with letrozole increased endogenous concentrations of LH and extended the lifespan of the dominant follicle, which delayed the next FSH surge and subsequent follicular wave emergence. Letrozole continues to have potential as a non-steroidal treatment for controlling ovarian function in cattle.
authors.affiliation: Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4, Canada.
authors.forename: M Jimena
authors.initials: MJ
authors.lastname: Yapura
authors.forename: Reuben J
authors.initials: RJ
authors.lastname: Mapletoft
authors.forename: Jaswant
authors.initials: J
authors.lastname: Singh
authors.forename: Roger
authors.initials: R
authors.lastname: Pierson
authors.forename: Jonathan
authors.initials: J
authors.lastname: Naile
authors.forename: John P
authors.initials: JP
authors.lastname: Giesy
authors.forename: Hong
authors.initials: H
authors.lastname: Chang
authors.forename: Eric
authors.initials: E
authors.lastname: Higley
authors.forename: Markus
authors.initials: M
authors.lastname: Hecker
authors.forename: Gregg P
authors.initials: GP
authors.lastname: Adams
mesh_terms: D000818:Animals; D001141:Aromatase / Q000737:chemistry / Q000378:metabolism; D047072:Aromatase Inhibitors / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology*; D002417:Cattle / Q000502:physiology*; D002478:Cells, Cultured; D003433:Crosses, Genetic; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000378:metabolism; D030762:Estrous Cycle / Q000187:drug effects; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D006107:Granulosa Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006207:Half-Life; D007275:Injections, Intravenous / Q000662:veterinary; D000077289:Letrozole; D007986:Luteinizing Hormone / Q000097:blood; D009570:Nitriles / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology*; D009866:Oogenesis / Q000187:drug effects; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000502:physiology; D010060:Ovulation / Q000187:drug effects*; D014230:Triazoles / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology*; D014463:Ultrasonography
chemical_list: D047072:Aromatase Inhibitors; D009570:Nitriles; D014230:Triazoles; D004958:Estradiol; D000077289:Letrozole; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D001141:Aromatase