Nitric oxide end products in patients hospitalized for diarrhoea

Increased nitric oxide (NO) has been demonstrated in inflammatory bowel diseases (IBD). Plasma and urinary nitrite and nitrate are usually considered to reflect global NO generation. Recently it has been suggested that plasma nitrate may be a discriminant indicator between infectious enterocolitis (IC) and IBD. To investigate this hypothesis we compared plasma and 24 h urinary nitrite and nitrate in 13 healthy controls, 44 patients with IBD [Crohn's disease (CD) n = 30; ulcerative colitis (UC) n = 14], 16 patients presenting with IC and seven chronic radiation enterocolitis (RE) patients.

Despite a trend towards higher plasma nitrate in IC (54.6+/-11.4 micromol/l) than in the other groups (CD: 38.4+/-4.8, UC: 34.8+/-8.4, RE: 34.7+/-7.5, controls: 31.1+/-5.2), this difference was not statistically significant. Urinary nitrate was higher in IBD, IC and RE than in controls, with no difference between these groups. Nitrite concentrations were not different. Nitrate levels were positively correlated with blood and 24 h urinary neopterin (e.g. plasma nitrate and blood neopterin: r = 0.54, P<0.0001), and in some cases, to C-reactive protein.

High nitrate (in our case only urinary nitrate) appears to be secondary to the magnitude of the inflammation rather than the aetiology of the diarrhoea. It should therefore more likely be considered as a marker of the severity of the inflammatory response rather than used as a discriminant indicator between IC and IBD patients.