Hormones, mimics reproductive

Xenobiotics can adversely affect the normal functions of the cells/organs of the reproductive system. These agents may induce a variety of outcomes, including prevention of ovulation and impairment of ovum transport, fertilization, or implantation. Endocrine disruptors may mimic endogenous hormones as well as directly destroy cellular components, leading to cell death. More indirect effects may include inhibition of key enzymes involved in steroid synthesis. 

Many chemicals are suspected of being endocrine disrupters. Such substances mimic the action of natural hormones, tricking the body into thinking that they are hormonal. In so doing, they may cause excessive action of the natural hormones or may act in an improper manner, thus having some sort of toxic effect. The greatest concern with endocrine disrupters is with reproductive effects and sexual development. But there is also concern that they may increase risk of some kinds of cancer, vascular disease, and diabetes. 

Prominent among toxicants that adversely affect both male and female reproductive systems are endocrine disruptors (see Section 9.7). Toxicants that mimic the actions of sex hormones are agonists, and those that prevent hormonal action or bind competitively to hormone receptor sites are antagonists,12 Male patients treated with cimetidine for peptic ulcers have exhibited low sperm counts and abnormal breast enlargement, a condition called gynecomastia. Gynecomastia has also been caused in men working in oral contraceptive production. Ketoconozole inhibits the enzymes required to produce hormones involved in sperm production and can immobilize sperm in seminal fluid. 

Methoprene and fenoxycarb mimic the action of insect juvenile hormone in molting and reproduction, and have low toxicity to mammals. Exposure at molting produces deformed insects having mixed larval/pupal or larval/adult morphologies, and they disrupt reproductive physiology in adults to effectively serve as a method of birth control. 

Hormone disruption refers to a chemical s ability to mimic or block the action of the body s own hormones, or its ability to interfere with normal hormone production or breakdown in some way. Chemicals that are able to disrupt sex and thyroid hormones have been particularly under the spotlight, but other hormones, such as those of the adrenal gland, may also be subject to disruption. The overall result appears to be damage to reproductive, immune, and nervous systems, and increases in birth defects, selected cancers, and learning disabilities. For the last three decades, there has been a disconcerting increase in the incidence of such human health disorders as breast cancer, testicular cancer, hypospadias (a birth defect where the urethra does not open at the end of the penis) and learning disabilities. 

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