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 μg of rhTSH, IM or IV, or 1 unit of bTSH, IM, respectively, in a crossover design. The 20 client-owned dogs received 75 μg of rhTSH, IV. Blood samples were taken before and 6 hours after TSH administration for determination of total serum thyroxine (T4) concentration. Additional blood samples were taken after 2 and 4 hours in Beagles that received rhTSH, IM.
Results—There was a significant increase in T4 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 T4 concentration between the 2 groups.
Conclusions and Clinical Relevance—Results indicated an equivalent biological activity of rhTSH, compared with bTSH. Use of 75 μg 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 T4 concentration was ≥ 2.5 μg/dL and at least 1.5 times basal T4 concentration.
Objective—To evaluate 4 methods used to measure plasma insulin-like growth factor (IGF) 1 concentrations in healthy cats and cats with diabetes mellitus or other diseases.
Animals—39 healthy cats, 7 cats with diabetes mellitus, and 33 cats with other diseases.
Procedures—4 assays preceded by different sample preparation methods were evaluated, including acid chromatography followed by radioimmunoassay (AC-RIA), acid-ethanol extraction followed by immunoradiometry assay (AEE-IRMA), acidification followed by immunochemiluminescence assay (A-ICMA), and IGF-2 excess followed by RIA (IE-RIA). Validation of the methods included determination of precision, accuracy, and recovery. The concentration of IGF-1 was measured with all methods, and results were compared among cat groups.
Results—The intra-assay coefficient of variation was < 10% for AC-RIA, A-ICMA, and AEE-IRMA and 14% to 22% for IE-RIA. The linearity of dilution was close to 1 for each method. Recovery rates ranged from 69% to 119%. Five healthy cats had IGF-1 concentrations > 1,000 ng/mLwith the AEE-IRMA, but < 1,000 ng/mL with the other methods. Compared with healthy cats, hyperthyroid cats had significantly higher concentrations of IGF-1 with the A-ICMA method, but lower concentrations with the IE-RIA method. Cats with lymphoma had lower IGF-1 concentrations than did healthy cats regardless of the method used.
Conclusions and Clinical Relevance—Differences in the methodologies of assays for IGF-1 may explain, at least in part, the conflicting results previously reported in diabetic cats. Disorders such as hyperthyroidism and lymphoma affected IGF-1 concentrations, making interpretation of results more difficult if these conditions are present in cats with diabetes mellitus.