Animal experiment:

Rats[2]Sprague-Dawley female rats (N=22) are used. Non-pregnant rats are divided into four groups: 1) control, 2) hypothyroidism, 3) hypothyroidism treated with low doses of L-Thyroxine (20 μg/kg/day) and 4) with high doses of L-Thyroxine (100 μg/kg/day). Control rats (group 1) are fed with standard diet, while the intervention rats are fed with iodine-free diet for 12 weeks to induce hypothyroidism (groups 2-4) which is continued for four more weeks to allow screening of hypothyroid status and L-Thyroxine-treatment. Food and water (iodine-free diet) are available ad libitum. The hypothyroid group treated with low (group 3) or high doses of L-Thyroxine (group 4) are injected intraperitoneally every 24 h with respectively 20 μg/kg/day and 100 μg/kg/day. Blood samples are collected for thyroid function screening at week 12 and 16 following the initiation of either the control or iodine-free diet. Hysterectomy is performed under general anesthesia (isoflurane 2%) at the end of the treatment and the two uterine horns are placed in physiological Krebs' solution until isometric tension measurements within no more than 1 h.