after injecting this rats with thyroxine, normal rat will become hyperthyroidic but will never suffer from goiter. injecting thyroxin into the system of the normal rat will elevate the levels of thyroid hormone in the blood making it to develop hyperthyroidism. the rat will not develop goiter because it has enough thyroid hormone in its system. goiter is enlargement of thyroid gland. this enlargement is occurs when this gland activities are increased in an attempt of producing enough hormone.