Sensitive, practical bioassay of thyrotropin, with use of FRTL-5 thyroid cells and magnetizable solid-phase-bound antibodies.
We have developed a new method for assessing the bioactivity of thyrotropin (TSH) in human serum by measuring cAMP production in FRTL-5 thyroid cells as an index of stimulation. To eliminate serum inhibitors of the cAMP response to TSH, we purified samples by mixing them with anti-TSH antibodies coupled to magnetizable particles. This method of immunoaffinity purification was simple and suitable for the measurement of a large number of samples. The detection limit of the bioassay was 3.13 milli-int. units of human TSH per liter. Intra-assay and interassay coefficients of variation ranged from 5.4 to 8.6% and from 12.6 to 21.5%, respectively. The concentrations of bioassayable TSH closely correlated with those of immunoassayable TSH, both in the immunoaffinity-purified samples (r = 0.946, P less than 0.001) and in the serum samples (r = 0.945, P less than 0.001) from 14 euthyroid subjects and 53 hypothyroid patients with Hashimoto's thyroiditis. The bioactivity-to-immunoactivity ratio was almost constant (0.84 +/- 0.30; mean +/- SD) over the range of concentrations of immunoassayable TSH in serum, 6.3 to 177 milli-int. units/L. We also demonstrate that the technique is applicable to measurements of bioactivities of circulating forms of immunoreactive TSH in different pathophysiological conditions.
Tokuda
Y
Y
Department of Nuclear Medicine, Kyoto University School of Medicine, Japan.
Kasagi
K
K
Iida
Y
Y
Hatabu
H
H
Hidaka
A
A
Misaki
T
T
Konishi
J
J
D000818:Animals; D000906:Antibodies; D001681:Biological Assay / Q000379:methods; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D006801:Humans; D008280:Magnetics; D011247:Pregnancy / Q000097:blood; D011869:Radioligand Assay; D051381:Rats; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism; D013967:Thyroiditis, Autoimmune / Q000097:blood; D013972:Thyrotropin / Q000097:blood*
D000906:Antibodies; D013972:Thyrotropin; D000242:Cyclic AMP