Inhibition of gap-junctional-intercellular communication in thyroid-follicular cells by propylthiouracil and low iodine diet

Propylthiouracil (PTU) or low-iodine diet (LTD) treatment increases thyroid-follicular-cell proliferation, possibly by disrupting the movement of small molecules ( < 1.2 kD) through membrane channels called gap junctions. Numerous tumor promoters and proliferative disease slates exhibit inhibited gap-junctional-intercellular communication (GJIC) prior to the induction of cell proliferation, yet the association between CJIC and apoptosis is unclear. In the present study, we used an ex vivo method to examine whether GJIC is inhibited in the thyroid of PTU- or LID-treated rats. Tn addition, the effect of these models of hypothyroidism on thyroid-follicular-cell proliferation and apoptosis was examined to determine the association between GJIC and cell homeostasis. After 14 days of treatment of either PTU or LID (plus 1% KClO4 in the drinking water), serum tri-iodothyronine (T-3) and thyroxine, (T-4) was decreased to nearly undetectable levels and serum TSH was increased in PTU- and LID-treated rats. At the same time point, GJIC was decreased 30-35% in PTU- and LID-treated rats while thyroid-follicular-cell proliferation increased nearly threefold in both treatment groups. Interestingly, apoptosis increased twofold in both hypothyroid treatment groups. These data suggest that PTU or LID treatment inhibit thyroid GJIC during a state of increased thyroid-follicular-cell proliferation and apoptosis. While the increase in proliferation was anticipated, the paradoxical increase in apoptosis during decreased GJIC in thyroid-follicular cells warrants further examination. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.