EN07 - Validation of the Thyrotropin-releasing Hormone Simulation Test in Healthy Cats

Abstract: Background – A thyrotropin-releasing hormone (TRH) stimulation test can be used to evaluate the integrity of the pituitary-thyroid gland axis. Administration of exogenous TRH (0.1mg/kg) to cats with normal thyroid function will increase thyroid stimulating hormone (TSH) and serum total thyroxine (tT4) concentrations. However, adverse side effects (vomiting, panting, hypersalivation) are common with that protocol.




Hypothesis/Objectives – To determine the lowest intravenous dose of TRH that adequately increases serum TSH and tT4 concentrations in normal cats. Our hypothesis was that TRH administered at doses lower than 0.1 mg/kg will adequately stimulate TSH and tT4 production in healthy cats and cause less side effects.




Animals – Six adult healthy research cats.




Methods – Cats were randomly administered 3 different doses of TRH (0.01, 0.05, or 0.1mg/kg) intravenously. Serum TSH and tT4 concentrations were measured using Immulite® 1000 at time 0, 30 and 60 minutes after TRH administration.

Results – All 3 TRH doses induced a significant TSH response (0.01 mg/kg, P = 0.0055; 0.05 mg/kg, P = 0.0017; 0.1 mg/kg, P = 0.0001). There was no statistical difference among the different TRH doses in stimulation of TSH (Figure 1). Only the lowest dose of TRH (0.01 mg/kg) induced an increase in serum T₄ concentration (P= 0.03). Administration of lower TRH doses (0.01 and 0.05 mg/kg) caused less side effects (1/6 cats) than did the highest concentration (0.1 mg/kg; 3/6 cats). 

Conclusions and clinical importance – TRH stimulation test induced a significant TSH response at all concentrations in adult healthy cats. The results suggest using lower TRH doses to decrease the side effects.