N-nitrosoproline in urine from patients and healthy volunteers after administration of large amounts of nitrate.

Urines from 12 healthy volunteers, sampled from 0-24 h after the volunteers had been administered 9.5 g sodium nitrate intravenously or up to 10.5 g ammonium nitrate orally, were analysed for N-nitrosoproline (NPRO). The mean NPRO content in urines voided just before administration of nitrate was 4.1 micrograms/L. Mean NPRO levels remained low until 6 h after nitrate intake. Mean NPRO contents in urines voided 6-8 h, 8-10 h, 10-15 h and 15-24 h after nitrate administration were 10, 40, 74 and 53 micrograms/L. respectively. The highest NPRO content found was 320 micrograms/L. These findings demonstrate that intake of one large dose of nitrate leads to enhanced nitrosation in the body, which lasts at least one day. Surprisingly, in urine from 21 patients who had been ingesting 2.5-9 g ammonium nitrate daily for several months to prevent the redevelopment of calcium phosphate renal stones, only slightly enhanced NPRO levels were found: less than 1-32 micrograms/L; mean value, 6.2 micrograms/L. In most of the urines, from the healthy volunteers as well as from the patients, N-nitrosothiazolidine-4-carboxylic acid was also detected. Results from the volunteers indicated that urinary excretion of this compound also increases several hours after intake of one large dose of nitrate.