The endocrine disruptor story gets more and more complicated as new research findings are revealed. One of the biggest, and probably most complex, mysteries is how substances with different shapes and structures produce similar physiological results. The most well studied effects are of compounds that simply bind to a hormone receptor and mimic or block normal hormone responses. It now appears that some environmental hormones produce their effects via elaborate signaling pathways and other complex modes of action that are independent of binding hormone receptors.
Receptors are protein molecules that read and respond to hormone signals.
Hormones and their receptors have compatible, interlocking shapes, something like two puzzle pieces or a lock and key. The activated hormone receptor then turns on specific genes, causing cellular changes that lead to responses typical of a ligand-hormone receptor complex. In the case of estrogen, these responses can include uterine growth in preparation for pregnancy or prevention of bone loss. One way foreign substances can mimic hormones is by binding to specific estrogen receptors inside a cell. At one point, scientists thought only a specific hormone could trigger a specific receptor into action, just like how only one key opens only one lock.