Use of recombinant human thyroid-stimulating hormone for evaluation of thyroid function in guinea pigs (cavia porcellus)

Objective-To evaluate the effects of administration of recombinant human (rh) thy- roid-stimulating hormone (TSH) for evaluation of thyroid function in euthyroid guinea pigs (Cavia porcellus). Design-Prospective, experimental study. Animals-10 healthy, sexually intact, pet guinea pigs (approx 1 year of age). Procedures-Guinea pigs were given rhTSH (100 μg, IM); plasma thyroxine concen- trations were determined prior to and 3 and 4 hours after rhTSH injection. The animals were housed in 2 groups on the basis of sex and fed different commercial mainte- nance diets according to their husbandry. Results-There was no significant difference in thyroxine concentrations between males and females before or after rhTSH injection. There was also no difference between thyroxine concentrations at 3 versus 4 hours after rhTSH injection. There was a significant difference between thyroxine concentrations before (median, 9.05 nmol/L [0.70 μg/dL]; 10% to 90% range, 7.39 to 16.99 nmol/L [0.57 to 1.32 μg/dL]) and after (mean ± SD, 23.95 ± 4.2 nmol/L) rhTSH injection. Euthyroid guinea pigs had plasma thyroxine concentrations of at least 7.30 nmol/L (0.57 μg/dL) and an in- crease of at least 2.6 times prestimulation thyroxine concentrations at 3 or 4 hours after stimulation. Conclusions and Clinical Relevance-The results suggested that rhTSH adminis- tered IM can be used for the TSH stimulation testing in guinea pigs. We suggest thyroxine concentration in a euthyroid guinea pig should at least double 3 to 4 hours after rhTSH injection.