Endocrine disruptors system

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine system because of the abihty of these chemicals to mimic or block endogenous hormones, or otherwise interfere with the normal function of the endocrine system. Chemicals with this type of activity are most commonly referred to as endocrine disruptors. Some scientists believe that chemicals with the ability to disrupt the endocrine system are a potential threat to the health of humans, aquatic animals, and wildlife. Others believe that endocrine disrupting chemicals do not pose a significant health risk, particularly in light of the fact that hormone mimics exist in the natural environment. Examples of natural hormone mimics are the isoflavinoid phytoestrogens (Adlercreutz 1995 Livingston 1978 Mayr et al. 1992). 

Successful reproduction (and sex) involves many complex chemical processes that can be disrupted at various points to reduce fertility and conception. Part of this process is under control of the endocrine system, and chemicals that affect the endocrine system are termed endocrine disruptors. In the 1950s, understanding of the endocrine system led to the development of birth control pills as a way to reduce fertility in humans. This is a desirable and planned use of endocrine disruptors. Subsequently, it was discovered that a number of chemicals released into the environment could disrupt the endocrine system and reduce fertility of wildlife. Some are concerned that exposure to these chemicals, such as DDT and dioxin (TCDD), may also affect human fertility (Table 17.1). Approximately 15% of couples of reproductive age are infertile. Endocrine disruptors may also affect fetal development, causing demasculization and feminization of the offspring, which in turn cause reduced fertility in the next generation. 

Depending upon the circumstance and desired effects, endocrine-disrupting chemicals can be either good or bad. The endocrine system is a finely balanced system responsible for fertility and many of the feminine and masculine traits we are all familiar with. Endocrine disruptors are used by millions of women in the form of the pill to control fertility. Chemicals in birth control pills subtly manipulate the endocrine system to reduce fertility. Unfortunately, we now know that many chemicals are capable of influencing the endocrine systems. When these chemicals, such as DDT and TCDD, are released into the environment, they reduce the fertility of wildlife. Exposure to endocrine disruptors is linked to decreased fertility in shellfish, fish, birds, and mammals. Endocrine disruptors such as nonylphenol have been shown to feminize male fish, interfering with reproduction. Some studies have also linked exposure to endocrine disruptors to decreases in human male sperm count. Ironically, urinary metabolites of the birth control pill as well as the female hormone estrogen pass through waste treatment plants and are released into the aquatic environment, where even small concentrations cause feminization of male fish. 

Most of the knowledge that we have regarding the interaction of chemicals with the endocrine system comes from in vitro receptor binding data. These receptor interaction data form the basis for many of the structure-activity relationships that have been derived for potential endocrine disruptors. It is important to note that potency measured in in vitro studies may or may not be relevant to the in vivo situation. The relative binding affinity (RBA) and potency of binding vary significantly within a given class of substances. For example, Branham et al. [11] reported... 

Endocrine disruptor. An exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism or its progeny or (sub)popu-lations. 

Dysfunction of the endocrine system could be due to either hyperfunction (excessive hormone production or responses) or hypofunction (insufficient hormone production or responses). Environmental chemicals that have the potential to perturb the endocrine system are known as endocrine or, synonymously, hormone disruptors. 

One study that overcomes some of the shortcomings of those just cited reported adverse neurodevelopment outcomes following maternal exposures to 19 organic solvents and mixtures of these. 13 In this study, the women were occupationally exposed to the chemicals listed in Table 24.3. Also included in this table are the K, values and whether or not the specific chemical is a known teratogen or a known endocrine disruptor. 5 It is interesting to note that only three of the chemicals in the study—ethanol, trichloroethylene, and mineral spirits (a mixture of hydrocarbon solvents)—are endocrine disruptors. This shows that teratogenic effects can be induced by chemicals and mixtures that are independent of the endocrine system. 

Anabolic steroids are not only reinforcing drugs, as are many narcotics, but they also interfere with the normal function of the endocrine system, and as such are endocrine disruptors. The presence of exogenous anabolic steroids in the blood causes a negative feedback in the brain, specifically the hypothalamus and the pituitary. This feedback leads to a reduction in the synthesis of gonadotropins —water-soluble hormones that travel in the blood to the testes, where they stimulate the synthesis of testosterone. This reduction... 

It is also clear that it is difficult to relate cause and effect to any specific chemical since, with the exception of point source effluents, many waterways contain a multitude of chemicals, of which the active endocrine disruptor may not be that which has been measured in the water or tissue. For such reasons, many studies have used in vitro experiments in which isolated tissue, either from a control animal or one captured in a polluted water system, is exposed to a single pollutant in the laboratory. Such experiments have shown significant disruption to testicular activity by a wide range of xenobiotics, including cadmium, lindane, DDT, cythion, hexadrin and PCBs. ... 

EC. 1999. Communication from the Commission to the Council and the European Parliament on Community strategy for endocrine disruptors, a range of substances suspected of interfering with the hormone systems of humans and wildlife. COM (1999) 706 Final. http / ec.europa.eu/environment/docum/99706sm.htm... 

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