Thyrotropin stimulation test–new perspective on value of monitoring triiodothyronine.

The research shows that in both horses and dogs, testing for increased triiodothyronine (T3) hormone levels is a quicker and more effective indicator of thyroid function post Thyrotropin (TSH) administration than testing for increased thyroxine (T4) levels.

Introduction

• The research study focuses on the triiodothyronine (T3) response to Thyrotropin (thyroid stimulating hormone; TSH) injection in horses and dogs.
• TSH is administered to stimulate the thyroid cells, and the subsequent increased concentrations of T3 and thyroxine (T4) in the serum of the subjects are studied.
• The primary aim of the research is to ascertain if testing for T3 can be used as a quicker measure of thyroid function following TSH administration than testing for T4.

Methodology

• In the study, horses were given 5 IU of TSH intravenously.
• It was observed that the T3 values in horses doubled 0.5 hours after TSH injection, with a peak response of 5 times the base-line value appearing 2 hours after injection.
• Similarly, dogs were administered with 0.2 IU TSH/kg of body weight and the maximum dose did not exceed 5 IU.
• The doubling of base-line T3 values in dogs was noticed at 1 hour, whereas T4 response doubled between 1.5 and 2 hours post-injection.

Results

• The peak releases of T3 and T4 in response to TSH in dogs had not fully developed by 4 hours.
• However, the percentage increase over base-line values at early sampling time points was greater for T3 than T4.
• This response resulted in an increased T3/T4 ratio in hypothyroid dogs.
• Overall, in both dogs and horses, these studies indicated that T3 response to TSH could be used as an earlier and more effective measure of thyroid function post TSH administration that that of T4 response.

Conclusion

• The findings of the study give a new perspective on the value of monitoring T3 levels post TSH administration in dogs and horses as a measure of thyroid function.
• This research may improve the effectiveness of thyroid function test for early detection and treatment of thyroid-related diseases in animals.