Hormonal oestrogens

Cells in the ovaries and testes produce the sex hormones oestrogen and progesterone in the female, and testosterone and androstenedione in the male (Chapter 19). 

The follicular phase covers the development of the follicle, which involves an increase in its size due to an increase in follicular fluid, growth of the ovum (i.e. an increase in the contents of RNA and protein) and an increase in the number of cells that surround the ovum. These cells are of two types, the granulosa and the thecal cells. The role of these cells is to synthesise and secrete the steroid hormones oestrogens (mainly oestradiol). The precursor molecule for their synthesis is cholesterol. There is a division of labour between these cells the thecal cells convert cholesterol into the male sex hormones androstenedione and testosterone, which are released into the blood to be taken up by the granulosa cells where they are converted to the oestrogens (Figure 19.8). For details of pathways, see Appendix 19.1. 

The control of the levels of the sex hormones, oestrogen, progesterone and testosterone, is achieved by feedback inhibition of the secretions of both the pituitary and hypo-... 

In the case of some oestrogenic chemicals (that mimic the effects of the female hormone oestrogen) it has been shown that what should be added to predict the combined effect of a mixture is not the effects of the individual chemicals but their concentrations (Silva et al, 2002). This means that a substance present at a concentration at which on its own it has no oestrogenic effect will contribute to the total oestrogenic effect of a mixture containing other oestrogenic chemicals. For such substances there is in practice no real threshold concentration below which they do not have an effect. Such no-effect levels are a crucial part of chemicals risk assessment, as I will explain in Chapter 7. 

These effects are irreversible and can be reproduced in fish in the laboratory. The male fish have now been found to produce a protein (vitellogenin, found in the yolk of eggs) that is normally produced only by female fish in response to the female hormone (oestrogen). Vitellogenin is produced by male fish both in polluted rivers and in the laboratory when they are exposed to known endocrine disruptors. The protein is used as a biomarker for this effect (see box). 

Substances that act like the natural hormones oestrogens. oncogenes Cancer genes. 

Hormones. Oestrogens, progestogens and androgens suppress lactation in high dose. Oestrogen/ progestogen oral contraceptives are present in amounts too small to be harmful but may suppress lactation if it is not well established. 

The conventional definition of the endocrine system is the collection of ductless glands that secrete small amounts of hormones directly into the blood of vertebrates. The hormones are transported to other parts of the body where they have a profound effect on biological processes. Perhaps the best examples are the sex hormones oestrogen and testosterone, but there are many others. Hormones are also produced by invertebrates (e.g. moulting hormones) and even by plants (e.g. growth hormones). 

Endosulfan, a chemical cousin of DDT that mimics the female hormone oestrogen in the human body was found illegally on 10 crops. 

There are four main types of steroid hormone (i) mineralocorticoids, (ii) glucocorticoids, (iii) the male sex hormones (androgens), and (iv) the female sex hormones (oestrogens) (Fig. 43.1). NB Androstenedione is the precursor of both the androgens and oestrogens. Indeed, a wit once noted that the only difference between Romeo and Juliet was the ketone group on the 3-carbon atom and the methyl group on carbon 10 of the steroid nucleus. 

These include the female sex hormones (oestrogens), the male sex hormones (androgens) and progesterone, as well as cortisol, aldosterone and corticosterone, which are produced in the adrenal cortex. The adrenal hormones have an important role in the control of glucose and fat metabolism. 

Because of its link with the KiSS-1 gene, kisspeptin has been suggested as a possible treatment for some forms of cancer. In particular, when breast and prostate cancers develop, they are often nurtured by the sex hormones oestrogen and testosterone (see p489 and pl85). If the production of these hormones could be switched off, the tumors should shrivel and die. One way to do... 

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