Levothyroxine acts like the endogenous thyroid hormone thyroxine (T 4 , a tetra-iodinated tyrosine derivative). In the liver and kidney, T 4 is converted to T 3 , the active metabolite. In order to increase solubility, the thyroid hormones attach to thyroid hormone binding proteins, thyroxin-binding globulin, and thyroxin-binding prealbumin (transthyretin). Transport and binding to thyroid hormone receptors in the cytoplasm and nucleus then takes place. Thus by acting as a replacement for natural thyroxine, symptoms of thyroxine deficiency are relieved.
Bufotoxins are a family of toxic steroid lactones . They occur in the parotoid glands , skin and poison of many toads ( genus Bufo ) and other amphibians, and in some plants and mushrooms.    The exact composition varies greatly with the specific source of the toxin. It can contain: 5-MeO-DMT , bufagins , bufalin , bufotalin , bufotenin , bufothionine , epinephrine , norepinephrine , and serotonin . The term bufotoxin can also be used specifically to describe the conjugate of a bufagin with suberylargine.