title: Thyroid function tests in euthyroid dogs treated with L-thyroxine.
abstract: The effects of treatment with L-thyroxine (1 mg/m2 of body surface/d, PO, for 8 weeks) on the thyroxine (T4) and triiodothyronine (T3) responses to thyrotropin (TSH) and thyrotropin-releasing hormone (TRH) administration were determined in 10 euthyroid Beagles; 4 other dogs acted as controls. The TSH response test was performed before treatment and at weeks 2, 4, and 8 of treatment in all dogs and at 2 and 4 weeks after cessation of treatment in 6 dogs. The TRH response test was performed before treatment and at week 6 of treatment in all dogs and at 5 weeks after cessation of treatment in 6 dogs. Suppression of the T3 response to TSH was evident at treatment week 2, whereas the T4 response was suppressed at week 4 and remained suppressed for the duration of the study. Four weeks after stopping treatment, T4 and T3 responses to TSH in 2 dogs were within the hypothyroid range. The T4 response to TRH was completely suppressed after 6 weeks of thyroxine treatment, but returned to pretreatment values by 5 weeks after cessation of treatment. Suppression of thyroid and pituitary function is evident after administration of a replacement dose of L-thyroxine to euthyroid dogs.
authors.affiliation: Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison 53706.
authors.forename: D L
authors.initials: DL
authors.lastname: Panciera
authors.forename: E G
authors.initials: EG
authors.lastname: MacEwen
authors.forename: C E
authors.initials: CE
authors.lastname: Atkins
authors.forename: W T
authors.initials: WT
authors.lastname: Bosu
authors.forename: K R
authors.initials: KR
authors.lastname: Refsal
authors.forename: R F
authors.initials: RF
authors.lastname: Nachreiner
mesh_terms: D000818:Animals; D004285:Dogs / Q000502:physiology*; D005260:Female; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology; D013960:Thyroid Function Tests / Q000662:veterinary; D013961:Thyroid Gland / Q000187:drug effects / Q000502:physiology*; D013972:Thyrotropin / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage; D013974:Thyroxine / Q000097:blood; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood / Q000494:pharmacology
chemical_list: D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D013974:Thyroxine