Endogenous hazards

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine system because of the abihty of these chemicals to mimic or block endogenous hormones, or otherwise interfere with the normal function of the endocrine system. Chemicals with this type of activity are most commonly referred to as endocrine disruptors. Some scientists believe that chemicals with the ability to disrupt the endocrine system are a potential threat to the health of humans, aquatic animals, and wildlife. Others believe that endocrine disrupting chemicals do not pose a significant health risk, particularly in light of the fact that hormone mimics exist in the natural environment. Examples of natural hormone mimics are the isoflavinoid phytoestrogens (Adlercreutz 1995 Livingston 1978 Mayr et al. 1992). 

Cancer. Studies found no relationship between endogenous p-cresol levels in the urine and the occurrence of large bowel cancer (Bone et al. 1976) or bladder cancer (Renwick et al. 1988) in humans. There are no data available regarding the carcinogenicity of exogenous cresols in humans. No cancer bioassays have been conducted in animals, but the results of a promotion study in mice suggested that cresols can be cancer promoters. Cresols have some ability to interact with mammalian DNA in vitro, but it is impossible to assess the potential hazard to humans without more information. 

The permeability of the skin to a toxic substance is a function of both the substance and the skin. The permeability of the skin varies with both the location and the species that penetrates it. In order to penetrate the skin significantly, a substance must be a liquid or gas or significantly soluble in water or organic solvents. In general, nonpolar, lipid-soluble substances traverse skin more readily than do ionic species. Substances that penetrate skin easily include lipid-soluble endogenous substances (hormones, vitamins D and K) and a number of xenobiotic compounds. Common examples of these are phenol, nicotine, and strychnine. Some military poisons, such as the nerve gas sarin (see Section 18.8), permeate the skin very readily, which greatly adds to then-hazards. In addition to the rate of transport through the skin, an additional factor that influences toxicity via the percutaneous route is the blood flow at the site of exposure. 

Grahmann H, Suchenwirth R. Thrombosis hazard in chlor-promazine and reserpine therapy of endogenous psychoses. Nervenarzt 1959 30 224-5. 

Burcham, P.C., Internal hazards baseline DNA damage by endogenous products of normal metabolism, Mutat. Res., 443, 11, 1999. 

---