Perchlorate Ion Enhances Mouse Thyroid Responsiveness to Thyrotropin, Human Chorionic Gonadotropin and Long Acting Thyroid Stimulator

Publisher Website
Google Scholar
Abstract
Perchlorate treatment of mice increased by 1.5 to 2-fold the thyroid secretory response to TSH [thyrotropin], hCG [human chorionic gonadotropin] and LATS [long-acting thyroid stimulator] in the McKenzie bioassay. Perchlorate alone did not increase basal plasma radioactivity. Perchlorate augmentation of the secretory response index was roughly proportional to the level of stimulation; it was similar for all 3 stimulators despite their different time courses of action which were unaltered by perchlorate; it was the same whether perchlorate administration preceded, coincided with or shortly followed injection of the stimulator, a finding in keeping with the slow clearance of this ion. The perchlorate effect was dose-related, although within a narrow range (6.25-12.5 .mu.g/mouse). Near-maximal perchlorate effect was obtained with a dose (12.5 .mu.g) which, when tested in different experimental conditions (MMI[methimazole]-blocked thyroid), discharged 80% of intrathyroidal radioiodide. Perchlorate exerted its augmenting effect by enhancing thryoid secretion: it increased plasma radioiodothyronines and radioiodide concentrations without decreasing the blood disappearance rates of iodide and iodothyronines. The potentiating effect of perchlorate probably takes place at a step prior to cyclic AMP action since it did not affect dbc[dibutyryl cyclic]AMP-stimulated secretion. The perchlorate effect may be indirect, through mobilization of minute amounts of intrathyroidal iodide.