Effects of dietary nitrite and nitrate on experimentally-induced inflammation in the rat

The inflammatory reaction was studied through changes in the weights and the constituents of granulomas induced by turpentine. The investigation used young rats fed ad lib for two months with diets containing 0.1% NO2-, 0.5% NO2-, 0.5% NO3- (w/w dry food). The NO2- and NO3- were incorporated into the diet in the form of their sodium salts. One normal control group was used as well as two groups which were "iso-sodium" with the treated groups (they received 0.636 g and 4.718 g NaCl/100 g dry food). Variance analysis was used for the statistical comparison of each group with its iso-sodium control. The growth of the animals dropped very significantly on nitrite treatment at both levels but for the nitrates only the stronger dose caused growth inhibition. The fresh weight of the granulomas decreased under the influence of the various treatments whereas the weight of the thymus was lower than the controls only in rats receiving the higher dose of nitrite. This decrease in the weights of the granulomas was paralleled by that of certain hydrosoluble and insoluble constituents of the inflamed tissue--in particular the total mucopolysaccharides and the collagen--but to a lesser extent by the non-fibrillar proteins. All these variations indicate a decrease in the defence mechanisms under the action of nitrites and nitrates. Various mechanisms could be involved: competition with iodine for capture by the thyroid, the hypoxic consequences of methaemoglobinaemia general nutritional effects, metabolic action during oxidations and peroxidations in the liver, or hormonal regulation of the adrenal glands. Analysis of the results also shows that the inflammatory reaction induced is a sensitive test in alimentary toxicology since effects are visible at doses of nitrates and nitrites which do not have nutritional consequences.