responses in the tissues of the body. One hormone molecule and the adenylate cyclase it activates can generate around one hundred cAMP molecules which can then activate one hundred kinase molecules. Each kinase, in turn, can stimulate hundreds of responses. Each stage of this amplification that occurs allows one hormone molecule to stimulate millions or billions of responses in the target cell in just a few minutes. When a hormone is no longer present at its receptor sites, phosphodiesterase breaks down cAMP and restores cell functions to their non-hormone stimulated state. The tropic hormones of the anterior pituitary, some of the hypothalamic releasing hormones, PTH, adrenaline, glucagon, gastrin, and secretin depend on the cAMP version of the two-messenger model of hormonal control. Insulin, however, relies on cyclic guanine monophosphate (cGMP) instead of on cAMP.
