Reproduction (2003) 125, 313–325 Review The impact of endocrine disruptors on oocyte competence P. Pocar 1 , T. A. L. Brevini 2 , B. Fischer 1 and F. Gandolfi 2 * 1 Department of Anatomy and Cell Biology, Martin Luther University, Halle (Saale) Germany; and 2 Department of Anatomy of Domestic Animals, University of Milan, 20133 Milan, Italy To date, approximately 60 chemicals have been identified as endocrine disruptors: exogenous agents that interfere with various aspects of natural hormone physiology. The potential reproductive and health hazards of these environmental chemicals have recently generated concern among the scientific community, policy makers and general public. The present review presents and discusses the available evidence that environmental chemicals are causing ovarian toxicity in various species, with particular attention to farm animals. The impact of chronic exposure to endocrine disruptors via food and drinking water cannot be neglected when studying fertility problems in these species. This review focuses attention on the superfamily of organochlorine chemicals, persistent organic pollutants (POPs), because of their persistence in the environment, ability to concentrate up the food chain, continued detection in environmental matrices and ability to be stored in the adipose tissue of animals and humans. Published data clearly indicate that POPs disrupt mammalian oocyte maturation and follicle physiology in every species studied so far, including farm animals. However, as most of the data available still derive from experiments performed on laboratory species or in vitro models, great care should be taken when extrapolations to other species or environmental situations are attempted. Recently, there has been concern among the scientific community, policy makers and general public regarding the potential reproductive and health hazards of a range of environmental chemicals known as ‘endocrine disruptors’. An endocrine disruptor is defined as an exogenous agent that interferes with the synthesis, secretion, transport, metabolism, binding, action or elimination of natural blood-borne hormones in the body that are responsible for homeostasis, reproduction and developmental processes (Kavlock and Ankley, 1996). Like hormones, small amounts of these chemicals (parts per trillion) are believed to affect the endocrine system of animals and humans. Three main types of endocrine-disrupting mechanism have been identified:  Mimics imitate naturally produced hormones such as oestrogen and testosterone. These chemicals can initiate chemical reactions in the body in the same way as naturally produced hormones.  Hormone blockers ‘lock up’ a hormone receptor, preventing naturally produced hormones from entering the cell and performing their function.  Triggers act through hormone-like pathways but initiate abnormal reactions in the cell that would not normally be produced by a hormone. The best-known triggers *Correspondence Email: fulvio.gandolfi@unimi.it are dioxin and dioxin-like chemicals. Dioxin acts through a hormone-like process to initiate entirely new responses. To date, approximately 60 chemicals have been iden- tified as endocrine disruptors. Chemicals with hormonal activity fall into three broad classes: (1) synthetic chemic- als used in industry, agriculture and consumer products; (2) synthetic chemicals used as pharmaceutical drugs; and (3) natural chemicals found in human and animal food (phytoestrogens). Examples of these substances are provided (Box 1). About half of these compounds are chlorinated, including dioxins (PCDDs), polychlorinated biphenyls (PCBs) and organochlorine pesticides such as DDT, methoxychlor, dieldrin and hexachlorcyclohexane (HCH). Exposure to endocrine disruptors can occur in a variety of ways; humans and animals can be exposed involuntarily to endocrine disruptors as a result of drink- ing contaminated water, breathing contaminated air, ingesting food or coming into contact with contaminated soil. Although endocrine disruptors have adverse effects on different hormone-dependent functions, for example, immune and thyroid dysfunction (Smialowicz et al ., 1989; Vos and van Loveren, 1995), studies have focused mainly on development and reproduction. The interference by endocrine disruptors of normal development of male and female reproductive organs as well as with reproductive functions in adulthood c  2003 Society for Reproduction and Fertility 1470-1626/2003 Downloaded from Bioscientifica.com at 06/18/2020 04:11:12AM via Massachusetts Inst of Technology