title: Effect of dexamethasone administration on serum thyroid hormone concentrations in clinically normal horses.
abstract: The effect that 5 consecutive days of treatment with dexamethasone (0.04 mg/kg of body weight, IM, q 24 h) would have on baseline concentrations of triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3), free T3 (FT3), and free T4 (FT4), and on response to thyroid-stimulating hormone (TSH) administration was determined in 12 clinically normal horses. Results of TSH response tests indicated that the horses could be placed into 2 groups: in 6 horses (group A), T4 concentration after administration of TSH was more than twice the baseline concentration; in the other 6 horses (group B), T4 concentration 6 hours after administration of TSH was less than twice the baseline concentration. Baseline serum concentrations of T3, T4, rT3, FT3, and FT4 were not significantly different between group-A and group-B horses. In both groups of horses, serum T3, T4, rT3, and FT4 concentrations were significantly increased 6 hours following TSH administration, compared with baseline concentrations. Treatment with dexamethasone resulted in significant (P < 0.05) increases in baseline concentrations of rT3 and FT3 in group-A horses and baseline concentrations of rT3 in group-B horses. The response to TSH administration following dexamethasone treatment appeared to be blunted with significant (P < 0.05) increases only in T3, T4, and FT4 concentrations in group-A horses and FT4 concentration in group-B horses. The magnitude of change in serum FT3 concentration in response to TSH administration was significantly less (P = 0.05) following dexamethasone treatment, compared with magnitude of change prior to dexamethasone treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia 65211.
authors.forename: N T
authors.initials: NT
authors.lastname: Messer
authors.forename: V K
authors.initials: VK
authors.lastname: Ganjam
authors.forename: R F
authors.initials: RF
authors.lastname: Nachreiner
authors.forename: G F
authors.initials: GF
authors.lastname: Krause
mesh_terms: D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D006736:Horses / Q000097:blood*; D008297:Male; D012016:Reference Values; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism; D013972:Thyrotropin; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*
chemical_list: D014284:Triiodothyronine; D003907:Dexamethasone; D013972:Thyrotropin; D013974:Thyroxine