PRINCIPLES OF TOXICOLOGY - Biology East Borneo

17 Properties and Effects of NaturalToxins and VenomsPROPERTIES AND EFFECTS OF NATURAL TOXINS AND VENOMSWILLIAM R. KEMThis chapter will discuss• Differences between poisons, toxins, and venoms• Major sites and mechanisms of toxin action• Important microbial, plant, and animal toxins• Animal venoms and their active constituents• Plants and animals causing contact dermatitis• Strategies for treating intoxications and envenomationsWe live in a world containing a wide variety of organisms—animal, plant, and microbial—possessingsubstances that are potentially harmful to our health. Fortunately for most urban inhabitants,the chances of developing morbid or fatal reactions to naturally occurring toxins arerelatively small. Still, even in an urban setting we are vulnerable to at least some natural toxins,such as those occurring in foods, our ornamental plants, or our places of habitation. Furthermore,as human populations expand into rural regions, they inevitably become more vulnerable topoisonous creatures.In this chapter we shall discuss some of the most common natural toxins, their mechanisms ofaction, and some modern principles of their treatment.17.1 POISONS, TOXINS, AND VENOMSFirst we need to understand what is meant by the terms: poison, toxin, venom. A poison is anysubstance or mixture of substances which can be life-threatening. Poisonous organisms eithersecrete or contain one or more chemicals (toxins) that seriously interfere with normal physiologicalfunctions. A toxin is a single substance with definable molecular properties that interferes withnormal function. Most toxins are exogenous substances made by an organism to adversely affectanother organism. However, even humans produce endogenous toxins (complement, defensins)to resist attack by foreign organisms such as bacteria and viruses. Venoms are secretionscontaining a mixture of biologically active substances, including enzymes, toxins, neurotransmitters,and other compounds. They are generally used both for prey capture and as a chemicaldefense against other predators. Some toxins are used solely as chemical defenses againstpredators, and in these cases, the toxins are often released from relatively simple integumentaryglands, and may even be stored within visceral organs. One example of such a toxin is pufferfishtoxin, which will be discussed below.Principles of Toxicology: Environmental and Industrial Applications, Second Edition, Edited by Phillip L. Williams, Robert C.James, and Stephen M. Roberts.ISBN 0-471-29321-0 © 2000 John Wiley & Sons, Inc.409