Abstract: Objective To determine whether atrial tissue shows alterations in electrophysiological proterties and in the expression and distribution of Cx43 in dogs with hyperthyroidism induced by Levothyroxine. Methods Sixteen mongrel canines of either sex weighing 12-17kg were randomized into control group (n=6) and L-thy group (n=10). Levothyroxin (80μg/kg) was administered daily by intraperitoneal injection for 8 months to all dogs in the L-thy group. Every 2 months atrial effective refractory period (AERP) was measured in both groups. Atrial tissues were collected at the 8th month. The expression of Cx43 in atria was evaluated with western blot analysis. Cx43 in atria was located by immunofluorescence and detected with Laser Scanning Confocal Microscope. Results compared with the control group, AERP of the L-thy group in the 4th, 6th and 8th month was significantly shorter (P<0.05). Levothyroxine significantly reduced the expression of Cx43 in left and right atrial (P<0.01), and the heterogeneous Cx43 down-regulation between left and right atria in the L-thy group was significant (P<0.05). Connexin43 located at the intercalated disc of atrial myocardium in the L-thy group was significantly reduced (P<0.01). Conclusions Thyroid hormone leads to atrial electrical remodeling and gap junction remodeling, involving heterogeneous reduction in Cx43 expression and disturbance in the distribution of Cx43. These changes are components of a variety of remodeling processes necessary, although not causative, for AF to become sustained.

Key words: Hyperthyrodism, connexin, gap junction, atrial fibrillation