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SECOND INTERNATIONAL SYMPOSIUM
ON THE ROLE OF SOY
IN PREVENTING AND TREATING CHRONIC DISEASESeptember 15-18, 1996
Brussells, Belgium
SCIENTIFIC PROGRAM
Satellite Symposium
Current Understanding of Soy and Infant Health
Phytoestrogens and Development in Animals: Is There a Biological Boundary Between Concern and Comfort Regarding Developmental Effects of Exogenous Hormonal Mimics?
Claude Hughes
Comparative Medicine Clinical Research Center, The Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, North Carolina, USA.The potent "activational" effects of hormones in mature animals are subject to multiple layers of redundant regulatory "feedback" restraints. Such redundancy and control makes internal homeostasis possible and is an important means by which the organism copes with potentially disruptive exposures to exogenous chemicals. Within certain bounds, despite exposures to hormone-like chemicals, these layers of regulatory mechanisms permit mature animals to maintain physiological stability (life and health). Since each particular exposure (characterized by dose, duration, properties of the chemical, metabolic status of the individual, age, etc.) differs, physiological flexibility in mature animals generally leads to adaptive responses. The direction of change of a response can be expected to differ under different scenarios; exposure to a short-lived agent that is episodic or repetitive can produce a drastically different outcome than that elicited by prolonged/continuous exposure or exposure to a persistent agent.
Epigenetic potent "organizational" effects of hormones in immature animals commonly appear to be irreversible and generally seem to be less well buffered by regulatory restraints. The sensitivity of animals to the actions of hormones during development and permanence of effects are key biological bases for particular concern regarding developmental exposures to any hormonal mimics, including phytoestrogens. The fact that adult-type redundant regulatory mechanisms are sequentially rather than instantaneously established during development is one key explanation for different "windows of sensitivity" for particular and differing outcomes due to exposures at different stages of development. Beyond dose, duration and pattern of exposure, the appearance of each adult-type homeostatic mechanism in the developing animal can change the direction of response of a biological endpoint relatively abruptly. Thus whether the prospects for organizational effects of an exposure are concerning (such as alterations in central nervous system development) or comforting (such as potential diminution in epithelial malignancies), a reasoned understanding of both potential risks and possible benefits will not be ascertained until meticulous and comprehensive studies are conducted.Soy Symposium Home http://soyfoods.com/symposium/
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