The Endocrine System of Fish

To fully understand how these pollutants can affect fish at very low levels, it is necessary to outline very briefly how the endocrine system works. It is a control system of the body which responds to internal and external signals to maintain the body in a chemical equilibrium, to regulate sexual development and the seasonal reproductive cycles, and to evoke a stress response to external threats. At its core are the hypothalamus and pituitary, which respond to neural signals from the brain and...

Fish Wildlife and HumansA Warning

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 disruptors 3 6 G. Vines, New Sci., 28 Nov. 1998, 26. in fish can therefore certainly be considered as potential endocrine disruptors in mammals, including humans. Fish thus provide an excellent biomonitor...

The Implications of Endocrine Dysfunction for Fish

There is now very clear evidence that a wide range of anthropogenic chemicals can be considered as potential endocrine disruptors in fish (Table 1), but it is rather less clear whether they cause actual endocrine disruption in intact animals 35 J. E. Harries, D. A. Sheahan, S. Jobling, P. Matthiessen, P. Neall, J. P. Sumpter, T. Tylor and N. Zaman. Environ. Toxicol. Chem., 1997, 16, 534. Table 1 Chemicals which can be considered as potential endocrine disruptors in fish2 Chlorfenvinphos,...

Effects in Women

Many studies have observed low incidences of hormone-dependent cancers, particularly breast cancer, in Asian countries compared with Western countries and it is becoming increasingly accepted that dietary factors play an important role. Although breast cancer can occur in either males or females, only about 1 of all cases occur in men, and male breast cancer is a rare disease in all parts of the world.41 Although there appear to be some similar risk factors for breast cancer in...

Evidence of Endocrine Disruption in Invertebrates

A wealth of laboratory-based evidence is available to illustrate endocrine disruption in marine invertebrates. Fingerman et al.2 has reviewed the effects of trace metals in crustaceans, in which disturbances of the hormonal control of moulting, limb regeneration, blood glucose level, colour changes and reproduction were seen. Cadmium2 and selenium3 are both strongly implicated in a range of effects in, for example, crustaceans and echinoderms. Both cadmium and selenium affect moulting in...

Steroid Deactivation

The liver contains cytochrome P-450 dependent mono-oxygenases, and reducing and conjugating enzymes that convert hormones into water soluble products which can be more easily excreted. Mono-oxygenase enzymes of the liver, which are closely related to enzymes in the adrenal gland and the gonads, are affected by copper, mercury and organotin, PCBs, PAHs, pulp mill effluent and municipal wastewater, but are unaffected by most organochlorine pesticides.2 Such changes 32 A. Hontela, Rev. Toxicol,...

The Expanding Definition of Endocrine Disruption

Originally, the concern over endocrine disruption was based almost entirely on perceived effects on the reproductive system and it was usual to refer to the chemicals concerned as oestrogen mimics or oestrogenic chemicals. Later, chemicals were found that could block oestrogenic responses anti-oestrogens or androgenic responses anti-androgens and it was soon recognized that chemicals could affect other elements of the endocrine system via interaction with hormone receptors other than those of...