The estrogen steroid hormones are estrane steroids. It contains characteristics found in the chemical nucleus of both estrogen and androgen hormones. It is an analogue of androgen steroid hormones like testosterone and DHT. Libido in males is linked to levels of sex hormones, particularly testosterone. The thyroid hormones thyroxine and triiodothyronine contain iodine. This is regulated partly through control of secretion of hormones from the pituitary gland. Excessive production of the thyroid hormones is called hyperthyroidism. Iodine is essential in the synthesis of thyroid hormones. Iodine is needed in trace amounts for the production of thyroid hormones such as thyroxine. Steroids have different biological roles as hormones and signaling molecules. It can lead to hyperthyroidism and consequently high blood levels of thyroid hormones (hyperthyroxinemia). It can be caused by increased levels of androgen hormones. Radiation therapy causes a gradual loss of production of other pituitary hormones with time. Distributive shock associated with adrenal crisis results from inadequate steroid hormones. Little is known about intracellular kinetics of thyroid hormones.