Estrogens species differences

Sumida, K., Ooe, N., Saito, K., and Kaneko, H. (2003). Limited species differences in estrogen receptor alpha-medicated reporter gene transactivation hy xenoestrogens. Journal of Steroid Biochemistry and Molecular Biology 84, 33 40. 

However, before any conclusions can be drawn on this subject, it is necessary to be certain that species differences are not obscured by methodological inadequacy. It is quite possible that certain estrogen metabolites have not yet been discovered because of unsuitable methods. A typical example of this is estriol, which had long been supposed to be an exclusively human metabolite (see Dorfman and Ungar, 1953). But, estriol was eventually detected as a metabolite of estradiol-17/8 in the rat (Hagopian and Levy, 1958 Breuer and Knuppen, 1960) and in avian liver slices (Mitchell and Hobkirk, 1959). 

Female sexual development and behaviour in mammals occurs by default and requires no ovarian secretion, and it is only in genetic males that the testis can secrete hormones which destroy this female pattern and superimpose that of the male. Sexual differentiation is not so well defined in fish, and larval exposure to both synthetic estrogens and androgens is widely used in aquaculture to produce monosex cultures. Endocrine disruption of sexual differentiation in fish may therefore reflect both the complexity and diversity of such processes between different species. Some care is required in use of the terms hermaphrodite and sex-reversal since a true hermaphrodite has both functional testes and ovaries and a sex-reversed fish is fully functional as its final sex—both produce the appropriate viable gametes. Such functional sex-reversal is not possible in mammals, but in some species of fish it is the normal developmental pattern. In most of the cases of hermaphroditism or sex-reversal reported in the non-scientific press, there is evidence only for a few ovarian follicles within a functional testis. This may be considered as feminisation or a form of intersex, and is very clearly endocrine disruption, but it is certainly neither sex-reversal nor hermaphroditism. In some cases the terms have even been used to infer induction of a single female characteristic such as production of yolk-protein by males. 

Exposure to estrogenic compounds through diet will differ for herbivores and carnivores, the latter being most likely to encounter endogenous steroids in their prey. Efficient uptake of steroids in mammals is illustrated by the use of the contraceptive pill, but routes of absorption in invertebrates remain to be determined. The relationship between endocrine disruption and metabolic toxicity, with reduced reproductive viability a secondary consequence of metabolic disturbance, also merits further study in invertebrate species. 

The yeast reporter gene assays not only assess for the interaction of the chemical with the hormone receptor, but also the ability of that receptor-chemical ligand interaction to activate the hormone DNA response element. It should be realized, however, that most of these systems have been developed with human and mammalian hormone receptors and differences in ligand potencies can occur between different animal species. A comprehensive review of in vitro assays for measuring estrogenic activity, and some of the issues of comparability, is provided by Zacharewski (1997). 

Sex differences in olfactory performance have been described for many mammals, implying hormonal differences. In domestic cats, as in other species, males typically perform flehmen in response to conspecific urine. But spayed females can be stimulated to show flehmen by administering testosterone. If paired with estrogen-treated females, they frequently inspect the genital area of the female partner and subsequently exhibit flehmen. Males flehmen in 80% of the time to either female or male urine that is applied to the naso-oral surface. Testosterone-treated females flehmen to 90% of the male urine samples, and to 70% of those from females (Hart and Leedy, 1987). 

K Cooper Rutgers University, New Brunswick, NJ Evaluate the affects of a number of different compounds dioxins, dibenzofurnas, oil and estrogenic compounds on both invertebrates and vertebrate species U. S. Department of Agriculture Cooperative State Research Service... 

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