Influence of hyperthyroid conditions on gene expression in rat extraocular muscles

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. 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. To simulate a chronically hyperthyroid state, T3 treatment was administered by intraperitoneal injections of 25 µg T3 (Sigma-Aldrich) 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. For RNA isolation, the extraocular muscles (EOMs) were removed, flash-frozen in liquid nitrogen and stored at -80 °C until further use.