Comparison of the biological activity of recombinant human thyroid-stimulating hormone with bovine thyroid-stimulating hormone and evaluation of recombinant human thyroid-stimulating hormone in healthy dogs of different breeds

Objective-To evaluate whether use of recombinant human (rh) thyroid-stimulating hormone (TSH) induces equivalent stimulation, compared with bovine TSH (bTSH), and to evaluate activity of rhTSH in dogs of various large breeds. Animals-18 healthy research Beagles and 20 healthy client-owned dogs of various breeds with body weight > 20 kg. Procedures-The 18 Beagles were randomly assigned to 3 groups, and each dog received either 75 mu g of rhTSH, IM or IV, or I unit of bTSH, IM, respectively, in a crossover design. The 20 client-owned dogs received 75 mu g of rhTSH, IV. Blood samples were taken before and 6 hours after TSH administration for determination of total serum thyroxine (T-4) concentration. Additional blood samples were taken after 2 and 4 hours in Beagles that received rhTSH, IM. Results-There was a significant increase in T-4 concentration in all dogs, but there were no differences between values obtained after administration of bTSH versus rhTSH or IV versus IM administration of rhTSH. Although there was a significant difference in age and body weight between Beagles and non-Beagles, there was no difference in post-TSH simulation T-4 concentration between the 2 groups. Conclusions and Clinical Relevance-Results indicated an equivalent biological activity of rhTSH, compared with bTSH. Use of 75 mu g of rhTSH, IV, did not induce a different magnitude of stimulation in large-breed dogs, compared with Beagles. Euthyroidism was confirmed if post-TSH simulation T, concentration was >= 2.5 mu g/dL and at least 1.5 times basal T, concentration.