KClO4 inhibits thyroidal activity in the larval lamprey endostyle in vitro

An in vitro experimental system was devised to assess the direct effects of the goitrogen, potassium perchlorate (KClO4), on ra-dioiodide uptake and organification by the larval lamprey endostyle. Organification refers to the incorporation of iodide into lamprey thyroglobulin (Tg). Histological and biochemical evidence indicated that endostyles were viable at the termination of a 4 h in vitro incubation. A single iodoprotein, designated as lamprey Tg, was identified in the endostylar homogenates by polyacrylamide gel electrophoresis andWestern blotting. Lamprey Tg was immunoreactive with rabbit anti-human Tg serum and had an electrophoretic mobility similar to that of reduced porcine Tg. When KClO4 was added to the incubation medium, both iodide uptake and orga-nification by the endostyle were significantly reduced relative to controls as determined by gamma counting, and gel-autoradiography and densitometry, respectively. Western blotting showed that KClO4 significantly lowered the total amount of lamprey Tg in the endostyle. Based on the results of this in vitro investigation, we conclude that KClO4 acts directly on the larval lamprey endostyle to inhibit thyroidal activity. These data support a previous supposition from in vivo experimentation that KClO4 acts directly on the endostyle to suppress the synthesis of thyroxine and triiodothyronine, resulting in a decrease in the serum levels of these two hormones