Effect of H2 blockers on intragastric nitrosation as measured by 24-hour urinary secretion of N-nitrosoproline.

Intragastric nitrosation of proline (500 mg daily) was studied in eight volunteers and three duodenal ulcer patients. Daily urine outputs of N-nitrosoproline (NPRO) and N-nitrosothiazolidine-4-carboxylic acid (NTCA) were measured for two days before, two days during and two days after ingestion of H2 blocker (ranitidine). No increase in NPRO output was found with ranitidine, the trend being clearly towards decreased intragastric nitrosation of this amine. A significant (p less than 0.05) increase in NTCA occurred during H2 blockade, due to increased concentration of NTCA in urine. The biological significance of the presence of NTCA in urine is uncertain.