Thyrotropin stimulation test--new perspective on value of monitoring triiodothyronine.
Thyrotropin (thyroid stimulating hormone; TSH) stimulus to thyroid cells of horses and dogs resulted in increased serum triiodothyronine (T3) concentrations that were detected earlier than those of thyroxine (T4). Doubling of the base-line T3 values in horses was detected 0.5 hours after injection of 5 IU of TSH IV, with peak response of 5 times base-line value detected 2 hours after injection. Doubling of T4 values in horses was noticed between 2 and 3 hours, with the peak response of 2.4 times base-line value at 4 hours after injection of TSH. Doubling of base-line T3 values in dogs in response to 0.2 IU TSH/kg of body weight (IV-5 IU maximum dose) was noticed at 1 hour, whereas T4 response doubled between 1.5 and 2 hours. Peak release of T3 and T4 in response to TSH in dogs had not developed by 4 hours; however, the percentage increase over base-line values was greater for T3 than T4 at early sampling time points, and this response has resulted in an increased T3/T4 ratio in hypothyroid dogs. Thus, in both dogs and horses, these studies indicated that T3 response to TSH could be used as a measure of thyroid function at earlier time intervals after TSH administration than one measures T4 response.
D000818:Animals; D004283:Dog Diseases / Q000503:physiopathology*; D004285:Dogs; D005260:Female; D006736:Horses; D007037:Hypothyroidism / Q000503:physiopathology / Q000662:veterinary*; D007273:Injections, Intramuscular; D007275:Injections, Intravenous; D008297:Male; D013268:Stimulation, Chemical; D013960:Thyroid Function Tests / Q000662:veterinary*; D013972:Thyrotropin / Q000008:administration & dosage / Q000494:pharmacology*; D013974:Thyroxine / Q000378:metabolism*; D013997:Time Factors; D014284:Triiodothyronine / Q000378:metabolism*
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine