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Other Hormone Systems The story of endocrine disruption began with discoveries that synthetic compounds could interfere with the action of estrogens, first by mimicking them (as with diethylstilbestrol and bisphenol A, both discovered as synthetic estrogens in the 1930s), and then by antagonizing them. The interference may be directly through binding with a specific hormone receptor, or indirectly, for example by altering the rate of synthesis or metabolic breakdown of a hormone. Now hormone disruptors have been shown to interfere with many more hormone systems (see below). The list keeps growing. With over 70,000 chemicals in commercial use today, the fact that synthetic hormone disruptors have not been identified for every hormone system is most likely due to the sheer volume of testing required. The cautious assumption would be that all chemically-mediated communication systems—of which hormones are one class—are vulnerable to disruption. |
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Thyroid Thyroid hormones play an important role in learning, memory, auditory function and behavior. They are essential for brain development because they regulate the proliferation and differentiation of neuronal cells in the fetal brain. Research on the disruption of the thyroid hormone system has involved three main areas of study:
The weight of the evidence indicates that thyroid disruption occurs in wildlife in polluted areas. In humans, several studies suggest that in utero exposure may affect fetal neurodevelopment and, later, childhood cognitive function, but the mechanisms are not well understood. |
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Progesterone In human females, progesterone is involved in the menstruation cycle, and during pregnancy acts to relax the smooth muscle allowing the cervix to expand. Progesterone is also involved in the biochemical pathway in the synthesis of testosterone. PCBs have been reported to interfere with the production of progesterone supported testosterone. The mechanism of this action is unknown but is not the result of direct progesterone receptor binding. There is, however, evidence that some chemicals will bind with the progesterone receptor. More... |
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Retinoids Retinoids are key hormones in vertebrate tissue differentiation and development, including limb development. Exposure in utero to excessive amounts of retinoic acid can have a teratogenic effect. The ability of the insect growth regulator, methoprene, has been reported to bind with retinoid receptors in mammals and amphibians. |
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Glucocorticoids Glucocorticoids play an important role in glucose regulation, as well as carbohydrate, lipid and protein metabolism. These adrenal hormones regulate immune, circulatory and renal function. Additionally, glucocorticoids influence growth (including weight regulation), development, bone metabolism and central nervous system activity. PCB metabolites have been reported to bind to glucocorticoid receptors. More... At extremely low levels (10 ppb), arsenic inteferes with glucocorticoid-receptor control of DNA transcription. This may be important in understanding the links between low level chronic exposure to arsenic, cancer and diabetes. More... |
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