THE TIME COURSE OF EXPERIMENTALLY ALTERED THYROID STATUS MANIFESTATIONS IN FEMALE C3H-A MICE
The female C3H-A mice with agouty fur color were used to model hyper- and hypothyroidism in the long lasting experiment. The study was carried out for 44 weeks. Hyperthyroidism was induced by the administration of the L-thyroxine injections on alternate days during the whole period of the investigation. Hypothyroidism was achieved by adding propylthiouracil to the drinking water. The change of thyroid state was characterized by biphasic change in body weight. At the beginning of the experiment the hypothyroid animals were retarding by their weight. Otherwise the hyperthyroid animals were advancing by their weight. But since the 18 <sup>th</sup>-21 <sup>st</sup> week the initial trends changed, i. e. the hypothyroid mice body weight started ahead the hyperthyroid one. In the open field test both hypo- and hyperthyroid animals demonstrated the higher level of the investigating activity in comparison with the euthyroid mice. In the hyperthyroid mice the frequency of side-activity acts (grooming) increased significantly. Thus, the hyperthyroid animals appeared to be more anxious. To the 18 <sup>th</sup> week of the experiment the animals of study groups started to demonstrate the apparent visual difference in their fur color. The hyperthyroid mice fur color became darker than one of the hypothyroid and the euthyroid mice. It is worthy of note that the hyper-thyroid mice fur color was getting lighter than one of the euthyroid animals. The results are discussed in the context of hypothalamic-pituitary-thyroid axis functioning. The possible mechanisms of hormonal regulation of the fur color in mice are considered to include the hypothalamic-pituitary-thyroid axis hormones activities.