Effect of Recombinant Human TSH on the Uptake of Radioactive Iodine (123i) by the Thyroid Gland in Healthy Beagles.

Campos M., Peremans K., Duchateau L., et al.

Conference Proceedings, (2010). American College of Veterinary Internal Medicine, Anaheim: p.684

In human medicine recombinant human TSH (rhTSH) increases the thyroid radioactive iodine uptake (RAIU) allowing radioiodine (131I) dose reduction and higher efficacy in the treatment of differentiated thyroid cancer and multinodular goiter. It can be expected that rhTSH has a similar effect in dogs. The goal of this study was to evaluate the effect of rhTSH, administered 24 h and 48 h before radioiodine (123I), on the thyroid RAIU in healthy dogs. 7 euthyroid healthy beagles were randomly divided in 3 groups in a prospective, blinded, cross-over study. On week 1, one group received 123I for a baseline RAIU, one group received 100 mg of rhTSH IV 24 h before 123I and one group received 100 mg of rhTSH IV 48 h before 123I. All dogs received 37 MBq of radioactive 123I IV and thyroid RAIU was determined 8 h, 24 h and 48 h thereafter. The study was designed in such a manner that each dog received the 3 treatments and a wash-out period of 3 weeks was respected between them. Blood samples were taken for measurement of serum total thyroxine (TT4) at baseline, 6 h, 12 h, 24 h and 48 h after rhTSH administration. rhTSH caused no significant change on thyroid RAIU. The over- all mean thyroid RAIU significantly decreased during the study independent of the treatment. rhTSH significantlyincreased serum TT4 concentration, which peaked 6 h after rhTSH administration. No adverse effects of rhTSH were observed during the study. Results suggest that 100 mg of rhTSH administered IV 24 h or 48 h before radioiodine have no influence on thyroid RAIU in healthy dogs. Further studies are needed to determine the best timing, dosage and route of rhTSH administration in healthy and thyroid carcinoma dogs.