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

Abstract

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(-3) 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(-4)-10(-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 less than 0.0025) from the control. However, 10(-5) mU/liter TSH produced a response significantly different (P less than 0.0025) from the control after an exposure time of 180 sec, and the range of the dose-response 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.