Role of Estrogen in the Endocrine System - Essay Example

ESTROGEN MIMICS Introduction The endocrine system which controls and coordinates many basic functions is one of the most complex systems in the humanbody. It is known that the normal functions of all organ systems are regulated by this system. The endocrine system controls maturation, development, growth, and regulation within the body. It consists of glands (such as the pituitary, the pancreas, the adrenals, and the testes) and hormones, which are natural chemical messengers. The endocrine glands secrete carefully measured amounts of these messenger chemicals into the bloodstream. They travel to different parts of the body and bind to specific receptors in order to control and adjust many life functions. Any small disturbances in endocrine function, especially during certain stages of the life cycle such as development, pregnancy, and lactation, can lead to profound and lasting effects (Kavlock, et al. 1996, 1-26). For example, estrogen is a hormone secreted primarily by the ovaries. It controls the menstrual cycle, fertility, and maintenance of a healthy pregnancy, among other critical activities in adults. In the fetus, estrogen is essential for normal development of both males and females (NRDC, N.D.). Scientists have identified dozens of human made chemicals that can disrupt endocrine system. For instance, some man made chemicals can act like estrogen in the body and are called “estrogen mimics”. Agricultural chemicals such as pesticides, herbicides, and fungicides are commonly known to mimic the activities of estrogen. These are being increasingly detected in agricultural runoff. Besides, effluent from water treatment plants often from drugs flushed down the toilet in homes and pollution from manufacturers including plastics factories and paper pulp mills also known for estrogen mimicking properties. These chemicals are also turning up in aquatic animals and birds that live in or near streams, rivers and the ocean. They are known -- in certain concentrations -- to disrupt the ability of alligators, frogs, birds and fish to mature and reproduce (Earth and Sky, 2000). Synthetic substances that can have the same effect as naturally occurring hormones in the body are called “hormone mimics” or "hormonally active agents (HAAs)" as the U.S. National Academy of Sciences termed them in a landmark report issued in August 1999. HAAs may be beneficial, such as the synthetic hormone drugs, estrogen and progesterone, that are found in birth control pills and in hormone replacement therapy taken by women after menopause. Many common foods, especially soy and other legumes and some vegetables, fruits and grains, naturally contain large quantities of HAAs with weak estrogen-like activity. These are called “phytoestrogens.” Dietary experts believe that a diet high in such foods may have beneficial effects on health. In addition, some industrial chemicals and some pesticides may have incidental hormone-like properties. Some scientists have hypothesized that the presence in the environment of low levels of these HAAs may interfere with naturally occurring hormones or with the normal function of the endocrine system, to cause possible adverse health effects. In this context, HAAs are often referred to as “endocrine disrupters” (American Chemistry Council, 2000, 1-108). Mechanism In order to explain the mechanism of how these synthetic chemicals interrupt the hormonal activities, scientists often use an comparison of “lock and key” to describe the way hormones and receptors work together. When the hormone (the “key”) meets the receptor (the “lock”), they join together just as a specific key fits into a specific lock. This results in certain signals to specific the cell or a group of cells to begin producing a specific protein or to perform some other specific function that the body needs. In general situations only one key opens any given lock. However, in the case of endocrine system that is not always the case. Occasionally a second key may be very similar to the first key, with some minor differences, and may actually open the lock. Sometimes the manmade hormones (i.e., “synthetic hormones”) that resemble naturally occurring hormones and can bind to the same receptor that binds natural hormones. When synthetic hormones bind to the receptors, they may produce the same effect in the body as naturally occurring hormones. Examples of such hormonally active agents (HAAs) are the man-made hormone drugs that are found in birth control pills. These man-made hormones fool the body by binding to the same receptors as the naturally occurring hormones, estrogen and progesterone, and thus prevent pregnancy (American Chemistry Council, 2000, 1-108). Environmental Estrogens A substance that produces the same effect on the body as natural estrogen is called an “estrogen mimic.” If it is manmade, either a drug intended to act as an estrogen or an industrial chemical with incidental estrogen-like properties, it is called a “synthetic estrogen.” If a synthetic estrogen is found in the environment, it is then referred to as an “environmental estrogen.” While some environmental estrogens are synthetic, many are not and are produced naturally by plants or fungi (American Chemistry Council, 2000, 1-108). Endocrine disrupting chemicals are suspected to be found in insecticides, herbicides, fumigants, and fungicides that are used in agriculture as well as in the home. Other endocrine disruptors are also found in industrial chemicals such as detergents, resins, plasticizers, and monomers in many plastics. Exposure to these chemicals occurs through direct contact in the workplace or at home, or through ingestion of contaminated water, food, or air. A few studies revealed that some of these chemicals leach out of plastics, such as the PVC plastics used to make IV bags. When these plastics, or other materials, are burned many unwanted byproducts that are endocrine disruptors or suspected endocrine disruptors are released into the air or water. The majority endocrine disrupting chemicals are fat-soluble. As a result, they do not get quickly flushed out of the body, and are accumulated in fat. These chemicals further bioaccumulate or concentrate up the food chain. In other words, very low levels of a chemical in the air, water, or soil result in higher levels in plant life, still higher levels in herbivores, and even higher levels in carnivores (NRDC, N.D.). Impact of Pesticides on Endocrine System and its Functions It is a well known fact that we need to eat a variety of fruits and vegetables daily in order to look and feel our best. But, along with vitamins, minerals, phytonutrients and fiber that these fruits and vegetables provide, several harmful residues of pesticides, fungicides and various chemical additives are also present in it. A recent USDA study showed that 73 percent of conventionally grown produce contained at least one pesticide residue. It does not include the chemicals used to make these produce look glossy, last longer or ripen on the truck as it makes the long journey from green fruit to grocery store shelf. These residues are not only harmful to plants but are also very harmful to human beings and other wild life. According to the USDA Pesticide Data Program (PDP) in 1996, a conventionally grown apple is likely to contain residues of at least four pesticides, and some individual apples had as many as 14 different residues. Other USDA research showed that over 90 percent of the tested conventionally grown apples, celery, peaches, pears, and strawberries had pesticide residues and likely contained multiple residues. Testing done by the PDP in 2002 determined that 72 percent of the apples tested were positive for the pesticide thiabendazole; ten percent had residues of cancer causing captan; and others had traces of highly toxic organophosphate insecticides, including phosmet (13 percent) and anzinphos methyl (37 percent). According to the Agency for Toxic Substances and Disease Registry, polycyclic aromatic hydrocarbons (PAH) are by-products of the partial burning of coal, gas and oil, and are used to make some pesticides. Studies show that PAHs cause tumors in laboratory animals through inhalation, via food, or through prolonged contact with skin. PAHs are also known xenoestrogens (“zeeno”-estrogens) or false estrogens, and they easily bind to estrogen receptor sites on our cells. Unlike the natural estrogen hormones that do their jobs and move on, estrogen-mimics aren’t as easy to turn off. They cause cellular functions to change, often with undesirable results such as the carcinogenic effects. False estrogens or synthetic estrogens have been associated with several forms of cancers. Though pesticides are essential agro-chemicals, and some might argue that xenoestrogens found in pesticide residues are present in levels that cause no observable effect (NOE) in laboratory studies, research indicates that combining a variety of xenoestrogens below NOE produces an estrogen-mimic effect (Petty, 2006). Besides, in agriculture a combination of different chemicals are sprayed seasonally in order to control pests and diseases. Today the use of these synthetic chemicals has become inevitable and farmers are highly dependent on these for plant protection. In developing countries even today extremely hazardous chemicals such as DDT, BHC, endosulfan etc are being used. These chemicals are banned in the developed nations. Pesticide spraying is important however, farmers need to follow sustainable agricultural practices and opt for more environmental friendly options when it comes to plant protection. Several pesticides are now known to interfere with normal hormonal function in human beings and animals (NRDC, N.D.). For example, Several organochlorine pesticides, including DDT, methoxychlor, endosulfan, and dicofol, mimic estrogen (Guillette, et al. 1994: 680-688; Cummings, 1997:367-379). Lindane, which is sometimes used to treat head lice in children, acts as an anti-estrogen, and is also toxic to the nervous system (Cooper, et al, 1989:384-394; Chadwick, et al, 1988: 147-158). Vinclozolin and iprodione, popular fungicides, both break down into a metabolite that interferes with testosterone and other androgens (Gray, et al, 1994:46-52). Atrazine, a popular herbicide, can disrupt ovarian function, cause mammary (breast) tumors in animals, and interferes with the binding of steroid hormones and the breakdown pathway of estrogen (Bradlow, et al, 1995: 147-150; Danzo, et al. 1997:294-301). Though no human studies have been done involving the endocrine effects of these chemicals, the endocrine system in animals is nearly identical with the human, making it likely that effects observed may be relevant to human health. In humans and animals, the endocrine system is critical to life. Disruption of hormone function can permanently alter normal development of the fetus and child (Tilson, 1998:807-811). Some pesticides have also been reported to be toxic to the immune system in animals (Thomas, 1995: 55-61). Testicular Cancer Endocrine-disrupting chemicals have been implicated as possible contributing factors in a number of diseases that afflict men and boys. Incidence of testicular cancer, and possibly of undescended testis and hypospadias (where the urethra opens, not at the tip of the penis, but along the shaft or scrotum), have increased (Greenpeace, October 2003). Sperm quality is low and appears to be still falling across many parts of Europe and the USA (Skakkebaek, et al. 2001: 972-978). The incidence of hypospadias doubled in the USA between 1970 and 1993 (Paulozzi, et al. 1997: 831-834). Testicular cancer has increased dramatically in some parts of the world and is now the most common form of cancer among young men in some countries (Hardell, et al. 1997: 828-830). Since the testes secrete the hormone testosterone and are regulated by hormones of the pituitary gland, it has been suggested that HAAs might cause testicular cancer. Results from studies that examined the incidence of testicular cancer in various countries were inconsistent with the “in utero hypothesis.” Specifically, the incidence of testicular cancer was found to be high in Denmark but low in nearby Finland despite similarities in economic development, diet and use of chemicals in these two countries. Also, in Bombay, India, a heavily polluted city where DDT (a pesticide with hormone-like properties) is still widely used, the incidence of testicular cancer is substantially lower than in Denmark or New Zealand where DDT is banned. Similarly, the incidence of testicular cancer varies from state to state in the United States, with the highest rates observed in the mountain states (as opposed to the industrial and agricultural states) of Montana, Idaho and Colorado (American Chemistry Council, 2000, 1-108). Female Fertility Disruptors In some parts of the world, girls are hitting puberty far younger than in the past, sometimes starting sexual development several years earlier than normal. A study in 2001 of children immigrating to Europe from parts of Latin America and Asia found that some girls started developing breasts before the age of eight and began their periods before they were ten (Krstevska-Konstantinova, et al, 2001: 1020-1026). Although scientists are unsure why this shift is occurring, exposure to the insecticide DDT in early life prior to immigration is one possible cause; high levels of the DDT breakdown product, DDE, were found in the blood of three - quarters of immigrating children exhibiting early puberty. Although DDT is banned in the developed world, many countries in the South and East continue to use it against malaria-carrying mosquitoes. DDT is rapidly transported worldwide and soon finds its way through the food chain to man. The pesticide is thought to have its effect because DDE mimics female oestrogen hormones. DDE, in combination with other oestrogen mimics, could trick a young girl’s body into entering puberty early. It is not unreasonable to assume that other synthetic mimics may have similar effects (Greenpeace, October 2003). It is now believed that xenoestrogens may contribute to ovarian cysts. Ovarian Cysts are products of failed or disordered ovulation. A functional ovarian cyst is formed when the follicle does NOT release its egg, and the follicle continues to grow forming a cyst.  An ovarian cyst can also be formed even if the follicle releases the egg, the hole where the egg is released closes up, the corpus luteum is not formed, and the cyst continues to grow (Smith, N.D.). Conclusion Several millions of new chemicals are introduced into the environment without the knowledge of their long-term effect on human and other animals. This calls for in depth research particularly on its impact on the endocrine system and its function. Several studies suggest the pesticides can have drastic impact on the endocrine system particularly in the form of xenoestrogens. Some of the studies on animals also suggest that these are carcinogenic in nature. A few independent researches suggest that pesticides and other harmful synthetic chemicals increase the risk of ovarian and testicular cancer. As far as the growing population is concern, it is important to feed them. And there is no doubt that pesticide play an important role in plant protection. However, it is essential that the focus need to be on sustainable farming, which reduces the overuse of synthetic pesticides and promotes the use of natural enemies, bio-pesticides etc. Adoption of such farming technique will not only benefit the present generation but also the future generations from their harmful effects. Work Cited American Chemistry Council, Chemicals in the Environment and the Endocrine System 2000, Arlington, 1-108, 4 April 2006, Bradlow, H.L., Davis, D.L., Lin, G., Sepkovic, D., Tiwari, R. Effects of pesticides on the ratio of 16 alpha/2-hydroxyestrone: a biologic marker of breast cancer risk. Environ Health Perspect 1995; 103 Suppl 7:147-150. Chadwick, R., Cooper, R., Chang, J., Possible antiestrogenic activity of lindane in female rats. J Biochem Toxicol 1988; 3:147-158. 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Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida. Environ Health Perspect 1994; 102:680-688. Hardell, L., Ohlson, C.G., Fredrikson, M. Occupational exposure to polyvinyl chloride as a risk factor for testicular cancer evaluated in a case-control study. Int J Cancer 1997; 73(6):828–830. Kavlock, R.J. et al., Research Needs for the Risk Assessment of Health and Environmental Effects of Endocrine Disruptors: A Report of the U.S. EPA-sponsored Workshop, Environ Health Perspect 1996; 104, Suppl 4:1-26. Krstevska-Konstantinova, M, Charlier, C., Craen, M., Du Caju, M., Heinrichs, C., de Beaufort, C., Plomteux, G., Bourguignon, J.P. Sexual precocity after immigration from developing countries to Belgium: Evidence of previous exposure to organochlorine pesticides. Hum Reprod 2001;16(5):1020–1026. Natural Resources Defense Council (NRDC), Endocrine Disruption - An Overview and Resource List 5 April 2006. Paulozzi, L.J., Erickson, D., Jackson, R.J. Hypospadias trends in two US surveillance systems. Pediatrics 1997;100(5):831–834. Petty, L. Dirty Details American Wellness Network, 5 April 2006, Skakkebaek, N.E., Rajpert-De Meyts, Main, K.M. Testicular dysgenesis syndrome: An increasingly common developmental disorder with environmental aspects. Hum Reprod 2001;16(5):972–978. Smith, E. The Cause of Ovarian Cyst- Xenoestrogens are Suspected of Causing Ovarian Cysts 6 April 2006, Thomas, P. Pesticide-induced immunotoxicity: are Great Lakes residents at risk? Environ Health Perspect 1995; 103:55-61. Tilson, H.A. Developmental neurotoxicology of endocrine disruptors and pesticides: identification of information gaps and research needs. Environ Health Perspect 1998; 106:807-811. Read More