Dorothy S. Smythe

EFFECTS OF BACTERIAL ENDOTOXIN ON METABOLISM : II. PROTEIN-CARBOHYDRATE BALANCE FOLLOWING CORTISONE. INHIBITION OF INTESTINAL ABSORPTION AND ADRENAL RESPONSE TO ACTH

Urinary nitrogen excretion over a 17 hour period without food and water was determined for mice poisoned with endotoxin and for control mice with and without the subcutaneous injection of 5 mg. cortisone acetate. Endotoxin did not alter the quantity of nitrogen excreted, compared with that of control mice, but in both groups of animals cortisone increased urinary nitrogen by the same amount. A balance between the quantity of protein catabolized (as estimated by increased urinary nitrogen excretion) and the total carbohydrate stored as a result of cortisone administration was found in fasted and in fed mice but not in endotoxin-poisoned mice. Endotoxin inhibited the motility of the gastrointestinal tract and blocked the absorption of food. Injections of ACTH in normal mice increased protein degradation and carbohydrate synthesis. In endotoxin-poisoned animals, ACTH failed to alter urinary nitrogen excretion and carbohydrate reserves. ACTH increased susceptibility to endotoxin. The number of heat-killed cells of S. typhimurium required to block the increase in urinary nitrogen caused by an injection of ACTH was found to be 10(8). A partial block was found with 5 x 10(7) cells but not with 10(5) cells. Mice infected with S. typhimurium excreted less than the normal amount of urinary nitrogen in response to ACTH 6 to 23 hours postinfection while normal amounts of nitrogen were eliminated 54 to 71 hours postinfection. The number of viable cells in the mice during the earlier period was less than the number of dead cells required to alter the nitrogen output, while the reverse was true during the later period.

SOME METABOLIC ASPECTS OF HOST-PARASITE INTERACTIONS IN THE MOUSE TYPHOID MODEL*

The influence of host metabolism on susceptibility to bacterial infections, primarily but not exclusively infections with Salmonella lyphimurium, has been studied for several years. I t was first shown that several of the well known inhibitors of specific steps in the tricarboxylic acid cycle, when injected at approximately the same time as the pathogen, reduced dramatically the mean survival time of experimental animals.’-* Also effective in reducing survival time were several intermediates of the same metabolic cycle.3 The extent to which the animals, albino mice, were succumbing to the infection itself, to the toxicity of inhibitor or intermediate, or to a combination of the two was impossible to assess. Until there is some basis for attributing cause of death to specific biochemical lesions in infections with organisms other than exotoxin producers, assessment will continue to be difficult if not impossible. I t was for this reason that the total number of viable pathogens in the mouse was determined.6s6 One of the advantages of using infections with S. typhimurium is the highly selective culture media available for its enumeration. These studies revealed a remarkably constant number of culturable cells of S. typhimurium at the moment of death irrespective of survival time and experimental procedure used to alter it. Approximately lo8 cells were consistently recoverable from the animals a t death. To this extent, it seemed justifiable to assume that altered host metabolism, under the conditions of the experiments, reduced survival time by permitting the “lethal” population of viable pathogens to be reached more rapidly? Within the framework of contemporary knowledge, further pursuit of this type of experimentation seemed to offer promising returns only if developments in related studies would be awaited. As D u ~ o s , * * ~ Pappenheimer,lo and 0ther~ll-I~ have suggested, the disease state in the infected animal may be the result of competition between host and bacterial parasite for an essential metabolite such as a growth factor, a vitamin, or an amino acid, or it may be the consequence of antimetabolite formation that interferes with an essential step in host cell metabolism by one mechanism or another. With the mouse and S. typhimurium, comparatively crude yet potentially revealing techniques yielded only negative evidence for metabolic competition between host and parasite (unpublished observations). It seemed essential, therefore, to paraphrase a 5tatement once made by Racker,” “to search for a thin metabolic trail left by Lhe pathogen in the forest of metabolism.” This search led us to a closer look at some of the effects of bacterial endotoxins in the hope that, a t least in mouse typhoid infections, it might be possible to relate disease symptoms to their presence, despite the important experiment of Hill ef ~ 1 . ’ ~ * The work reported in this paper was supported in part by a grant from the National Science Foundation, Washington, D.C., and by Contract A F 41(-657)-267 between Bryn Mawr College and the School of Aviation Medicine, United States Air Force Aerospace Medical Center (ATC), Brooks Air Force Base, Texas.