Nitrate and nitrite in saliva and urine of inhabitants of areas of low and high incidence of cholangiocarcinoma in Thailand.

: Cholangiocarcinoma is one of the main liver diseases in northeast Thailand. Associations with exposure to liver fluke and N-nitrosodimethylamine in formation of the tumour have been demonstrated in animals. This study was carried out to compare possible endogenous formation of N-nitroso compounds in inhabitants of areas with low and high incidences of cholangiocarcinoma by examining the levels of nitrate and nitrite in their saliva and urine. Thirty-two subjects (16 males and 16 females) living in the north-east (high incidence) and 12 volunteers (6 males and 6 females) in Bangkok (low incidence) were allowed to take regular meals, and their saliva and urine were collected before, and 30, 60 and 120 min after each meal. Nitrate and nitrite concentrations in saliva of the group in the high-incidence area were significantly higher than those of the group in Bangkok: salivary nitrate was 2-2.8 times higher and nitrite 2-5.6 times higher in the north-eastern group when compared with levels at each corresponding time interval in the low-incidence group. Nitrate levels in urine were also significantly higher in the north-eastern group at some time intervals, but urinary nitrite levels were similar and very low in both groups throughout the day. This finding may indicate a greater possibility of in-vivo formation of N-nitroso compounds in the north-east area than in Bangkok and might be associated with the occurrence of cholangiocarcinoma in north-east Thailand.