Ishizawa M, Utsunomiya T, Kinoshita N, Endo H
J Natl Cancer Inst. 1979 Jan;62(1):71-7.
The formation of methylnitrosocyanamide (MNC), a carcionogenic N-nitroso compound, from methylguanidine (MG) and NaNO2 in simulated gastric juice (SGJ) and in the stomachs of rats was quantitatively investigated. With a reverse mutation assay in which a tester strain of Salmonella typhimurium was used, MNC formation was shown to increase linearly for about 40--60 minutes after the incubation of MG with NaNO2 in SGJ. However, it decreased rapidly thereafter. The initial rate of MNC formation was directly proportional to the initial molar ratio of MG to NaNO2, but the yields of MNC depended only on the amount of MG added and were fairly constant (0.3--0.5% of the initial MG). MNC did not form at a pH above 2.5 or in the presence of 2% casein in SGJ at pH 1.2. It decomposed rapidly in SGJ at pH 1.2 with a half-life of approximately 2 minutes, whereas it was stable in phosphate buffer at pH 7.0. Following concurrent administration of MG and NaNO2 via stomach tube, MNC formation was detected in the pylorus-ligated stomachs of rats preconditioned with a casein-free dextrin diet but not in those of rats preconditioned with a casein-containing or synthetic diet. The yields of MNC observed 40--60 minutes after administration of reactants ranged from 0.02 to 0.05% of the initial MG. The possible environment significance of MNC formation in vivo was considered.
对甲基胍（MG）和亚硝酸钠（NaNO₂）在模拟胃液（SGJ）以及大鼠胃中形成致癌性N-亚硝基化合物甲基亚硝基氰胺（MNC）的过程进行了定量研究。采用鼠伤寒沙门氏菌测试菌株的反向突变试验表明，在SGJ中MG与NaNO₂孵育后，MNC的形成在约40 - 60分钟内呈线性增加。然而，此后迅速下降。MNC形成的初始速率与MG和NaNO₂的初始摩尔比成正比，但MNC的产量仅取决于添加的MG量，且相当恒定（为初始MG的0.3 - 0.5%）。在pH高于2.5时或在pH 1.2的SGJ中存在2%酪蛋白的情况下，不会形成MNC。它在pH 1.2的SGJ中迅速分解，半衰期约为2分钟，而在pH 7.0的磷酸盐缓冲液中稳定。通过胃管同时给予MG和NaNO₂后，在以无酪蛋白糊精饮食预处理的大鼠幽门结扎胃中检测到MNC形成，但在以含酪蛋白或合成饮食预处理的大鼠胃中未检测到。在给予反应物后40 - 60分钟观察到的MNC产量为初始MG的0.02%至0.05%。考虑了体内MNC形成可能的环境意义。
