EFFECT OF ENDOTOXIN ON HORMONAL RESPONSES TO THYROTROPIN AND THYROTROPIN-RELEASING-HORMONE IN DOGS

Objective-To determine whether administration of endotoxin affects thy roid gland function in dogs. Animals-24 Beagles. Procedure-Dogs were g iven thyrotropin (TSH) or thyrotropin-releasing hormone (TRH) on 2 occ asions. Twenty-four hours before the second challenge with TSH or TRH, all dogs were given 5 mu g of endotoxin/kg of body weight. Serum conc entrations of thyroxine (T4), free T4 (fT4), 3,3',5-triiodothyronine ( T3), reverse T3, autoantibodies to T3, and plasma concentrations of AC TH and cortisol were determined. Results-Treatment with endotoxin was associated with reduced baseline concentration of serum T3 and increas ed baseline concentration of reverse T3 and free T4. Endotoxin treatme nt resulted in reduced peak serum concentration of T4 after TSH and TR H. However, peak serum concentration of fT4 after TSH and TRH were not affected by endotoxin. Conclusions-A single dose of endotoxin affects several aspects of thyroid gland function in dogs, including T4 bindi ng, deiodinase activity, and the thyroidal response to TSH and TRH. Cl inical Relevance-Acute or chronic nonthyroidal illness may affect thyr oid gland function in dogs. Determination of fT4 concentration may pro vide a means of differentiating the effects of nonthyroidal illness fr om those of thyroid dysfunction, because endotoxin treatment was assoc iated with increased baseline serum free T4 concentration and unchange d peak serum fT4 concentration after administration of TSH or TRH.