A sensitive method for detecting in vivo formation of N-nitrosomorpholine and its application to rats given low doses of morpholine and sodium nitrite.
A method was developed to monitor the in vivo formation of N-nitrosomorpholine. N-Nitroso(2-hydroxyethyl)glycine, a major urinary metabolite of N-nitrosomorpholine, was quantified as its methyl ester-trimethylsilyl ether derivative, using gas chromatography with nitrosamine-specific detection. When the method was applied to rats, the in vivo formation of, or exposure to, as little as 0.6 micrograms of N-nitrosomorpholine could be quantified. The method was also applicable to human urine, with a detection limit of approximately 0.5 micrograms of N-nitroso(2-hydroxyethyl)glycine per 100-ml urine sample. The formation of N-nitrosomorpholine was measured in rats treated by gavage with a wide range of doses of morpholine and NaNO2. Depending on the dose, 0.5 to 12% of the morpholine was nitrosated. N-Nitrosomorpholine formation showed a high degree of variability among rats treated with a given dose of morpholine and NaNO2, but the levels of N-nitrosomorpholine formed were generally in agreement with expectations based on in vitro studies in which dependence on morpholine concentration multiplied by nitrite concentration squared has been established. The formation of N-nitrosomorpholine was also measured in rats administered a diet containing 50 ppm of morpholine and 1000 ppm of NaNO2, a regimen which has been previously shown to induce liver cell tumors in 58% of the animals. The mean daily formation of N-nitrosomorpholine under these conditions was estimated to be 0.88 +/- 0.59 mumol/rat (S.D.), which is high enough to account for the observed tumor incidence. The results of this study provide quantitative support for the assumption that in vivo formation of N-nitrosomorpholine leads to tumor development.
D000818:Animals; D002250:Carbon Radioisotopes; D002273:Carcinogens / Q000378:metabolism*; D004032:Diet; D007700:Kinetics; D008297:Male; D009025:Morpholines / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D009602:Nitrosamines / Q000032:analysis / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D011919:Rats, Inbred Strains; D012977:Sodium Nitrite / Q000378:metabolism*
D002250:Carbon Radioisotopes; D002273:Carcinogens; D009025:Morpholines; D009573:Nitrites; D009602:Nitrosamines; C002741:N-nitrosomorpholine; C037574:morpholine; D012977:Sodium Nitrite