ENVS 1030 Lecture Notes - Endocrine Disruptor, Nerve Growth Factor, Testicular Cancer

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Published on 1 Aug 2012
University of Guelph
Environmental Sciences
ENVS 1030
Chapter 9: Environmental Endocrine Disruption:
Some chemicals unintentionally interfere with hormone function in animals and in
some cases in humans.
A wave of interdisciplinary research over the past few years has been demonstrated
that chemicals in our environment can interfere with endocrine function.
In adults the endocrine system exhibits the ability to recover from fairly significant
perturbations, in the fetus even minor change in hormone levels can result in
lifelong effects.
Historical background:
A study in laboratory animals have demonstrated that estrogenic properties of a
number of industrial chemicals including bisphenol A, now widely used in plastics,
resins and dental sealants.
Hormonally active chemicals are widely used for beneficial medical purposes, but
adverse effects also occur.
Diethylstilbestrol (DES) daughters have an increased risk of reproductive and
immunological abnormalities, while sons are at risk of genital anomalies and
abnormal spermatogenesis.
Examples of DES indicate that fetus rather than the adult may be most at risk from
adverse effects of hormonal disruption.
Mechanisms of Action and Fetal Vulnerability:
Some pesticides and other industrial checmicals can directly bind to or block
hormone receptors, thereby initiating or blocking receptor-activated gene
transcription—the production of protentis from genetic information.
Other environmental chemical act indirectly on hormonal balance by altering
hormone production, hormone transport on hormonal balance by altering hormone
production, hormone transport on binding proteins, receptor numbers on target
organs or hormone metabolism.
Polychliroinated biphenyls (PCBs) interfere with thyroid function by a variety of
mechanism, including increased metabolism of the thyroid hormone T4., interfere
with T4 delivery to the developing brain by displacement from the carrier protein
and interfere with the conversion of T4 to the active form of thyroid hormone
known as T3.
During development, the fetus is more sensitive to hormonal fluctuation.
Low level exposure to hormones or toxicants may result in permanent physiological
changes not seen in adults exposed at similar levels.
Subtle hypothyroidism during fetal and neonatal life causes disruption of
neurotransmitters, nerve growth factors, nerve cell growth and normal energy
production in the developing brain, altering cognitive and neuromotor development.
Potential Health implications:
Reported abnormalities in labortoary animals and wildlife exposed to endocrine-
disrupting chemicals include feminization of males, abnormal sexual behaviour,
birth defects, altered sex ratio, lower sperm density, decreased testis size, altered
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