Endocrine system disruption 266

Detection of developmental effects induced by endocrine system disruption is discussed in chapter 5. Significant effects on any of these measures may be considered adverse if the results are consistent and biologically plausible. 

A second problem concerns delimiting the mechanisms of action which should be included in the definition, to exclude effects which are a secondary consequence of overt toxicity in other body systems. For example, disruption to the endocrine system caused by general metabolic disturbance, such as in severe liver damage, should not be grounds for calling a chemical an ED. 

The liver plays an important role in the endocrine system. The concentrations of hormones in plasma, and the activity of the glands which secrete them, are determined by the rate at which they are deactivated by the liver. The liver also has a major function in female reproduction since it is the target tissue of ovarian estrogen, to which it responds by producing the yolk protein vitellogenin. " Xenobiotics that affect either of these functions can therefore be considered to be potential endocrine disrupters. 

Fish have many advantages as experimental models in the study of endocrine disruption, and although they do have some significant differences in their endocrine system to that of mammals, the underlying basis is very similar. Chemicals which are shown to be either actual or potential endocrine disrupters... 

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). 

As onr knowledge of the pathways of effects for EDCs has evolved, the number of chemicals classified as EDCs has increased, and a more extensive list of these chemicals is detailed later in this chapter. The terminology used to describe chemicals that affect the endocrine system has also changed over time. Some now refer to EDCs as endocrine-active or endocrine-modulating, rather than endocrine-disrupting chemicals, as they do not necessarily always have deleterious effects. 

Endocrine disrupters Chemicals that cause disturbances of the endocrine system (e.g., by acting as agonists or antagonists of the estrogen receptor). 

All OCPs are polytropic, parenchymatous poisons, afflicting the central nervous system, liver, kidneys, the heart muscle, the stomach and intestines, and the endocrine system (mostly the adrenal glands, thyroid, and ovaries). Morphological changes in warm-blooded creatures poisoned by OCPs vary from insignificant disruptions in circulation and reversible dystrophy to focal necroses these effects depend on the organism, the dose of OCP, how long the OCP remains active, as well as on other factors [9, 39, 40, A47, A79]. 

An increase in plethora and focal dystrophic changes in the endocrine system matches clinical observations of changes in adrenal and thyroid function, as well as changes in local and general vascular dystonia, all detected in humans poisoned by OCP. Morphological changes in the brain s nerve cells conform to information on the disruption of reflex activity in the early stages of OCP exposure. 

Pesticides have a statistically reliable effect on children in zones where OCPs are intensively used (in the Salyansk region of Azerbaijan, the amount of OCPs introduced into humans exceeded public health standards by up to 7.7 times). Primary illness of the endocrine system increased 3.1 times in children up to age 15 (over a five year observation period) in disruptions in diet and metabolism, the nervous system, and the sensory and respiratory organs in increased frequency of illness (over five years) in children up to age 15 (an overall increase by 3.6 times, and by class of illness, from 2.2-7.6 times) in the prevalence of pathological disruptions according to data from medical examinations of children from 8-14 years (an overall increase by 2.3 times, and by class of illness by 2.0-8.4 times) in... 

ZEA resembles the human 17P-oestradiol hormone produced by theovaries. Although almost non-toxic, in very small doses it has oestrogenic effects that can disrupt the human endocrine system (Benbrook, 2005). It is important to note that transformation products of ZEA can have three to four times higher endocrine disrupting activity than ZEA. 

From these studies, some patterns of effect potentially mediated by the endocrine system have been observed. These include the accumulation of vitellogenin in ticks [50-52] and accelerated ovarian development in beetles and ticks [51, 53]. Different researchers have attributed these effects to a range of different mechanisms, including induced excitation of neurosecretory cells releasing juvenile hormone [50], and ecdysteroid disruption either by blocking the neuropeptide itself or at the epidermal site of synthesis [51]. Other researchers have not corroborated these results and have even found contradictory effects, e.g., suppressed ovarian development [52], Therefore at present for SPs, there is no clear evidence for adverse population-relevant effects with an underlying endocrine mode of action. 

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