Summary
Concentrations of serum thyroxine (T4) and 3,3′ ,5-triiodothyronine (T3) were determined in 7 clinically healthy adult dogs before and after administration of freshly reconstituted thyrotropin (tsh) and tsh that had been previously reconstituted and frozen for 1, 2, and 3 months. The 4 tsh response tests were performed at 30-day intervals by collecting blood samples for serum T4 and T3 determinations before and 4 and 6 hours after iv administration of tsh (0.1 U/kg of body weight). Baseline serum concentrations of T4 and T3 were similar at each of the 4 sample collection times over the 3-month period of the study. Mean serum concentrations of T4 and T3 increased significantly (P < 0.01) over baseline values after administration of freshly reconstituted tsh or tsh that had been previously frozen for 1, 2, or 3 months. Significant difference was not found in the mean post-tsh serum T4 or T3 concentration after injection of freshly reconstituted tsh or tsh that had been previously frozen for 1, 2, or 3 months. In 2 of the 7 dogs, mild reactions—mild ataxia and weakness—were observed during the last of the series of tsh response tests (ie, after iv administration of tsh that had been previously frozen for 3 months). Results of this study suggest that for use in dogs, reconstituted tsh stored at — 20C maintains adequate biological activity for at least 3 months. The ability to store reconstituted tsh for a longer period than the recommended 48 hours represents an economic advantage, because it allows clinicians to perform more tsh response tests per vial of tsh.
