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Time-Related Thyroid Stimulation by Thyrotropin and Thyroid-Stimulating Antibodies, as Measured by the Cytochemical Section Bioassay^*

Subdepartment of Molecular Biophysics, Department of Nuclear Medicine, The Middlesex Hospital Medical School London WIN 8AA, England

Address requests for reprints to: Dr. Patricia A. Ealey, Subdepartment of Molecular Biophysics, Department of Nuclear Medicine, The Middlesex Hospital Medical School, Mortimer Street, London WIN 8AA, England.

The time course of response of thyroid sections in the cytochemical bioassay to either TSH or thyroid-stimulating antibodies is bell shaped. The maximal staining for lysosomal naphthylamidase activity achieved was found to be the same regardless of the dose of stimulator applied; however, the rate at which the maximum was attained was dose dependent. Sections exposed to 10^–1 mU/liter TSH showed a maximal response at 120 sec, and those exposed to 10^–1 mU/liter TSH showed a maximal response at 210 sec. A similar dose-time effect was seen with immunoglobulin G from a thyrotoxic patient. Thus, by selecting a specific exposure time, a dose-response curve to the stimulator was obtained. A dose-response curve to a range of concentrations from 10^–410^–1 mU/liter TSH was obtained by exposing sections to the hormone for 90 sec. TSH (10^{– 3} mU/ liter) produced a response significantly different (P < 0.0025) from the control. However, 10^–5 mU/liter TSH produced a response significantly different (P < 0.0025) from the control after an exposure time of. 180 sec, and the range of the doseresponse curve at this exposure time was 10^–6-10–^–3 mU/liter TSH. Each point on these two dose-response curves was determined in quintuplicate, and precision profiles were constructed. The assay performed at 90 sec had a lower relative precision of 30% at a dose of 10^–1 mU/liter TSH, and at 180 sec, the best lower relative precision achieved was 80%. Thus, the sensitivity of the assay was improved by increasing the exposure time of the sections to TSH, but with a resultant loss of relative precision.

^* This work was supported by a grant from the Medical Research Council of the United Kingdom.

Received July 22, 1980.