Effects of endocrine active substances in wildlife species: Genetic,
biochemical, and physiological factors in variable susceptibility to
endocrine disruptors
S. Kawai, M. Kobayashi, and H. Kaneko
Department of Human Environmental Sciences, Kobe College,
4-1 Okadayama, Nishinomiya, Hyogo 662-8505, Japan;
Department of Biology, Division of Natural Sciences, International Christian
University, 3-10-2 Osawa, Mitaka,Tokyo 181-8585, Japan;
Sumitomo Chemical Co.Ltd., 27-1, Shinkawa 2-chome, Chuo-ku, Tokyo 104-8260,
Japan
Abstract: Responses to endocrine active substances (EASs) in
animals are various, and differences between the responses among individuals,
populations and species are well known. These differences are observed
not only in EASs but in most environmental chemicals including synthetic
and naturally occurring ones. The basic differences in sensitivity to
EASs are attributed to that of affinity or specificity of the receptors
to EASs at the cellular level. Although the nucleotide sequences encoding
for estrogen receptor proteins have been documented in several species
and the functions of the receptors are the same, the ability to bind
the natural hormones and the estrogenic xenobiotics is not necessarily
identical. The reproductive endocrine system is basically common among
vertebrates, but chemical types of hormones, physiological roles of
hormones and the basal blood levels of hormones differ among each species,
especially in sex steroids. These differences cause various types of
responses and sensitivity to EASs among animal species. Xenobiotic metabolism
is important for the genetical, biochemical and physiological factors
concerning the influence of EASs. Some EASs directly inhibit cytochrome
P450 (CYP) activity as was reported in tributyltin that inhibits CYP19
(aromatase) activity causing imposex in neogastropods. Some organochlorines
including dioxins stimulate aryl hydrocarbon (Ah) receptor-mediated
xenobiotic metabolism, and result in the metabolic disruption of steroid
hormones such as estrogen as were reported in eggshell thinning in birds
of prey and uterus occlusion in seals. CYP activity greatly differs
among wildlife species in both terrestrial and aquatic organisms, and
these differences are significantly responsible for the multiple effects
or toxicity of EASs. Sex and age differences also cause different responses
to EASs and are largely due to the differences in xenobiotic metabolizing
activities.
*Report from a SCOPE/IUPAC project: Implication of
Endocrine Active Substances for Human and Wildlife (J. Miyamoto and
J.Burger, editors). Other reports are published in this issue,
pp. 1617-2615.
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