title: Autoregulation of thyroid iodide transport: evidence for the mediation of protein synthesis in iodide-induced suppression of iodide transport.
abstract: The role of protein synthesis in iodide-induced suppression of subsequent iodide transport (iodide autoregulation) was studied in cat thyroid slices. Thyroid slices were pretreated for 60-120 min in the presence or absence of either excess (30 microM) sodium iodide, inhibitors of protein synthesis, or both. Tissue was then washed in the presence of 2 mM methimazole to prevent subsequent iodination reaction and remove excess iodide. Iodide transport activity was finally evaluated by measurement of the ratio of tissue to medium iodide concentrations in 90-min incubations. Addition of 0.1 mM cycloheximide during the preexposure of thyroid tissue to excess iodide had no effect on either control levels of iodide transport or iodide-induced autoregulation. However, if thyroid tissue was treated with cycloheximide alone for 1 h before preexposure to excess iodide, there was a significant reduction in the degree of iodide-induced induced autoregulation. Similar results were obtained with pretreatment of the tissue with 0.5 mM puromycin and 1 microgram/ml emetine. These findings suggest that protein synthesis is involved in the mechanism of thyroid autoregulation of iodide transport. Cycloheximide had no effect on the ability of excess iodide to reduce TSH-stimulated cAMP formation. Two-dimensional gel electrophoresis-isoelectric focusing and Sephadex G-25 column chromatography employing dual-isotope comparison of iodoprotein labeling of control and cycloheximide-treated tissue suggest that the ability of cycloheximide to suppress iodide-induced autoregulation is associated with the reduced iodination of an 8- to 10-kilodalton soluble component of the thyroid gland.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002415:Cats; D002417:Cattle; D003513:Cycloheximide / Q000494:pharmacology; D004640:Emetine / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects; D066298:In Vitro Techniques; D007454:Iodides / Q000378:metabolism*; D007467:Iodoproteins / Q000502:physiology; D008970:Molecular Weight; D014176:Protein Biosynthesis; D011691:Puromycin / Q000494:pharmacology; D012756:Sheep; D013961:Thyroid Gland / Q000378:metabolism*
chemical_list: D007454:Iodides; D007467:Iodoproteins; D011691:Puromycin; D003513:Cycloheximide; D004640:Emetine