Influence of hyperthyroid conditions on gene expression in rat tibialis anterior

Extraocular muscles (EOMs) are a highly specialized type of tissue with a wide range of unique properties, including characteristic innervation, development, and structural proteins. Even though EOMs are frequently and prominently involved in thyroid-associated diseases, little is known about the immediate effects of thyroid hormone on these muscles. In order to create a comprehensive profile of changes in gene expression levels in EOMs induced by thyroid hormone, hyperthyroid conditions were simulated by treating adult Sprague-Dawley rats with intraperitoneal injections of 25 μg T3 per 100 g body weight over the course of six weeks; subsequently, microarray analysis was used to determine changes in mRNA levels in EOMs from T3-treated animals relative to untreated controls. RNA isolated from tibialis anterior muscles of the same animals was used as a reference fast-twitch muscle. Adult Sprague-Dawley rats (initial body weight 200 ± 40 g) were fed ad libitum with standard laboratory diet and tap water. Eight rats were randomly divided into a T3-treated and a control group, three males and one female each. To simulate a chronically hyperthyroid state, T3 treatment was administered by intraperitoneal injections of 25 µg T3 (Sigma-Aldrich, St. Louis, MO, U.S.A.) per 100 g body weight. Injections were administered every second day over a period of six weeks. 24 hours after the last injection, the animals were sacrificed by CO2 asphyxiation, muscles were dissected immediately after death. Each of the four biological replicates in each group was used for a single microarray each. RNA from EOMs was used. Tibialis anterior RNA from the same animals served as a fast-twitch reference muscle.