Thyroid Hormone Assays T3 and

Measurement of thyroid hormone concentrations in the serum has become an important final step in the endocrine safety pharmacology procedures (Capen 1992, O Connor et al. 2002). Basal concentrations are measured in serum samples in the morning before treatment (to avoid artefacts by the in diurnal fluctuation of thyroid hormone concentrations). In contrast to the rise in TSH after a test injection of TRH (dynamic function test), there is no pronounced rise after TRH stimulation. However, in specific situations, the secretion of thyroid hormones may be stimulated by the injection of a biosynthetic TSH preparation. 

Standard radio-immunoassay procedures are applied, nowadays mainly solid phase assays which can be rapidly performed and evaluated, they are also several enzyme-linked immunoassay (ELISA) procedures from commercial suppliers. It is recommended to perform an internet check for the most appropriate method at the time of the study (for example DSL 2005). Methods have been described for triiodothyronine (Nejad et al. 1975, Chopra etal. 1972a, Larsen 1972a, 1972,) and for thyroxin (Chopra etal. 1971, Chopra 1972). The use of assays based on thyroxin binding globulin (Chopra et al. 1972b) is no longer recommended and cannot be applied to the rat, because the rat does not have this binding protein. However, for the human, measurement 

The usual procedure for radio-immunoassay data is calculation by a computer programmme, from standard curves of the hormone to be measured, it is important to have a sufficient number of animals per group, to be able to perform analysis of variance and statistical evaluation by tests of significance 

There are now many methods of RIA and ELISA design available for the rat and dog thyroid hormones. It is recommended that each laboratory performs an onsite validation for the methods to be selected for routine evaluation of endocrine safety pharmacology. 

CapenCC (1992) Pathophysiology of chemical injury of the thyroid gland. Toxicol Lett 64-65 P381-388 Chopra IJ, Solomon DH, Ho RS (1971) A radio-immunoassay of thyroxine. J Clin Endocrinol 33 865-868 Chopra IJ (1972) A radioimmunoassay for the measurement of thyroxine in unextracted serum. J Clin Endocrinol Metab 34 938 

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