In addition to interference with the endocrine system’s ability to synthesize and secrete hormones, exogenous chemicals can disrupt a hormone’s normal function in several ways. These foreigners can mimic some hormones and hence can bind to those target cellular sites receptive of the natural hormones. When these receptors mistreat an intruder as the natural hormone, they respond as they would to the hormone. In mimicking the natural hormone, some intruders can serve as inhibitors by reducing the number of receptors for binding. Some other intruders can cause the body into over-responding as more receptors are activated.

Still some exogenous chemicals, such as the insecticide lindane and the herbicide atrazine, can modulate the metabolic pathway of certain sex hormones (e.g., Crain et al., 1997; Hayes et al., 2002). There are also some intruders that can activate enzymes that speed up the metabolism of some hormones. For example, certain enzymes in the testes are known to be capable of metabolizing estrogens (Toppari, et al., 1996). These enzymes can break down an estrogen rapidly to a form where the target receptors can no longer recognize this hormone. Either way, some exogenous chemicals can directly or indirectly modify the metabolic pathways of certain hormones substantially. Such a disruption in turn can cause the natural hormone not to be able to bind to the target receptors at the right time or in the right manner.

In short, the modes of endocrine disruption include mainly, but are not limited to, agonistic and antagonistic receptor binding, and those actions that affect the biosynthesis, storage, release, transport, and clearance of hormones (Kavlock, et al., 1996). In either case, hormonal functions can be altered substantially, possibly leading to a severe health outcome.