Oestrogenic and antiandrogenic chemicals in the environment: effects on male reproductive health

Exposures of human populations to pesticides and industrial pollutants, and to synthetic chemicals present in foods, beverages, and plastics, have rai sed concern that these substances can interfere with endogenous sex hormone function. Interference with sex hormone action can, in turn, result in a v ariety of developmental and reproductive anomalies. Compounds in this class are thus referred to as endocrine disruptors (EDs). EDs that affect reprod uctive processes in vertebrates act primarily by altering oestrogenic and a ntiandrogenic activities. The recent cloning of a second oestrogen receptor (ER) subtype (ER beta) and its widespread tissue distribution pattern indi cates that the first ER to be cloned, ER alpha, may not be the only, or eve n the primary, mediator of oestrogen action. It is anticipated that this di scovery will lead to development of antagonist compounds specific to either ER subtype, and help to determine the function of each receptor subtype in reproductive and other tissues. Growing evidence suggests that EDs interfe re with reproductive function at low exposure levels and cause distinct eff ects at different concentrations within the same organ. Developing organism s have increased susceptibility to the actions of EDs because differentiati ng tissues are more vulnerable to changes in hormonal milieu. Thus, childre n are at greater risk of toxicant-related illnesses than adults. However, m ost data are collected from laboratory studies, and it remains to be determ ined that the levels of chemicals in the environment can impair human repro ductive health. There is also significant genetic variability between human and animal species in their reactions to chemicals. The effects of low-dos e, chronic, and multiple chemical exposures warrant further investigation i n order to characterize the risk of environmental agents to humans. The aim s of this review, which will focus on male reproduction, are to: 1) identif y synthetic chemicals in the environment that fall into the ED class; 2) de scribe their mechanisms of toxicity in reproductive tissues; and, 3) outlin e the direction of future research efforts with respect to EDs.