PHYSICO-CHEMICAL DEFENSE OF VERTEBRATE ORGANISMS: THE ROLE OF BILE ACIDS IN DEFENSE AGAINST BACTERIAL ENDOTOXINS LÓRÁND BERTÓK* The discovery of the causes of many infectious diseases and the resultant elaboration of more effective protection against them has produced the illusion in the minds of some researchers that it would only be a matter of time before the pathogenic agent of every infectious disease and the specific protection against it is fully worked out. Furthermore, the persistent search for new specific defense (active and passive immunization ) and antiinfectious (antibiotic) agents has resulted in the overshadowing of the investigation of natural, so-called nonspecific defense mechanisms. Over the years it has become obvious that there were some infectious agents against which the organism seemed incapable of developing sufficient specific immunologic defenses. A number of these infectious agents are gram negative bacteria. Sepsis and toxemia caused by some of these agents may be catastrophic despite the use of antibiotics . According to recent statistics, 300,000 persons in the United States have developed gram negative sepsis in hospitals, and approximately 100,000 of them have died annually [1, 2]. Dyspepsie colitis of neonates induced by Escherichia coli and perhaps other gram negative organisms may be an instructive disease within this general category. This enterotoxemia occurs quite frequently in newborn domestic animals (pig, calf) and more rarely in newborn humans; deaths of neonatal domestic animals as a result of this enterotoxic disorder are of considerable economic importance [3-7]. Despite the fact that these enterotoxemias have been known for many years, their pathogenesis is barely understood. The disorder is apparently due to several different gram negative intestinal organisms. Neither the classical immunologic methods (vaccination) nor antibiotic therapy has led to reliable means of prophylaxis or therapy. Since endotoxins derived from the bacterial cell wall have been recognized as the toxin responsible for ?Head, Department of Applied Radiation, Frédéric Joliot-Curie National Research Institute for Radiobiology and Radiohygiene, Budapest, Hungary. Supported in part by the Scientific Research Council, Ministry of Health, Hungary (6-13-1001-0/B). 70 I Lóránd Bertók ¦ Bile Acids in Defense the development of enterotoxemia, the question of natural, nonspecific resistance must be considered. On the basis of early work in our laboratory and recent reports drawn from the literature, the possible role of bile acids in the defense against the noxious influence of these bacterial endotoxins has finally been recognized. It has long been known that the toxic effects of bacterial endotoxins under experimental conditions can only be induced when they are administered parenterally [5, 8]. Although naturally occurring enterotoxemia results from absorption of the endotoxin from the intestinal tract, parenterally (intraperitoneal or intravenous) administered endotoxin causes prostration, diarrhea, and circulatory disturbances indistinguisable from those observed in the natural disease [5, 7, 9]. At autopsy animals killed by parenterally administered endotoxin which died in endotoxin shock show changes that are similar to the natural diseases (intestinal edema, hemorrhages) [9]. The experimental models differed from natural diseases only in the mode by which endotoxin entered the blood circulation. Thus the induction of"enteroxtoxemia" by parenteral endotoxin injection has served as a useful experimental model [10-12]. Our examinations have shown that there are phylogenetic correlations of endotoxin sensitivity [5]. Some species are more sensitive than others to administered endotoxin. Thus, man, horse, cattle, and guinea pigs demonstrate extreme sensitivity; birds are sensitive only in a certain embryonic stage, and amphibians and fishes are absolutely resistant [13]. The sensitivity appears to increase as one ascends the phylogenetic scale. Given orally, endotoxin is without effect in even the most sensitive species, when given in doses from 500 to 3,000 times the minimal parenterally lethal dosage. It is also ineffective when the intestinal mucosa of the experimental animal has been damaged by the injection of a histamine liberator or ionizing radiations [8]. There is no in vitro evidence for the existence of an intestinal enzyme which could specifically decompose the endotoxins and thus produce resistance to the orally administered material [14]. As a matter of fact orally administered endotoxin can be recovered essentially unaltered from the gastrointestinal tract by means of a phenol-water extraction...