Introduction: What is Environmental Endocrinology?

Most animals live in environments in which important physical and biologic factors vary both periodically and aperiodically. The maintenance of internal stability (homeostasis), and indeed the very survival of the individual, requires appropriately correcting physiologic and behavioral adjustments. These adjustments are based on information (signals) from external and/or internal sources detected (transduced) by adequate sensory receptors, and transmitted by nerve fibers to the central nervous system (integrating centers), where it is “processed” and transmitted to effectors, either as efferent nerve impulses, or as changes in the plasma levels of hormones. The maintenance of internal stability also requires feedback components between the effectors and various sites of the afferent communication system. Endocrine glands and hormones are essential components of both functions. It is now recognized that many nerve cells have typical endocrine functions (neurosecretion), while virtually all other nerve cells communicate with effectors by means of chemical transmitters. The distinctions long made among neurotransmitters, neurohormones, releasing factors, and hormones have become somewhat blurred. Thus, in a sense, the concept of environmental endocrinology, like those of many biologic “disciplines” in general, is an artificial consequence of reductionism.