Increased endogenous nitrosation in smokers.

Endogenous nitrosation of proline was investigated in smokers and nonsmokers. Volunteers consumed a volume of beetroot juice equivalent to 325 mg nitrate and, 1 h later, 500 mg proline. In separate experiments, volunteers ingested proline alone. Twenty-four-hour urines were collected and analysed for N-nitrosoproline. When proline was ingested alone, there was no significant difference in urinary N-nitrosoproline excretion between smokers and nonsmokers. When beetroot juice and proline were consumed, however, smokers produced approximately 2.5 times as much N-nitrosoproline as nonsmokers. Salivary nitrite levels of smokers and nonsmokers, both before and after consumption of beetroot juice, were not significantly different. Salivary thiocyanate levels were approximately 3.2. times higher in smokers than in nonsmokers. Our results suggest that the higher level of salivary thiocynate in smokers is responsible for the increased rate of endogenous nitrosation of proline in that group when compared with nonsmokers. Oxides of nitrogen in cigarette smoke do not appear to play a significant role.