NITRIC-OXIDE CONCENTRATION IN THE GAS-PHASE OF THE GASTROINTESTINAL-TRACT IN MAN

Nitric oxide (NO) has been implicated in various aspects of physiologi cal regulation in the gastrointestinal tract. Hence, measurement of lu minal NO concentrations is of interest for studying physiological and pathophysiological alterations in NO generation; however, at present, no reliable measurement techniques are available. Here we describe nov el approaches for measurement of NO concentrations directly in the gas phase of the stomach and colon in healthy subjects and patients. Stud ies were conducted in young healthy volunteers (n = 13). intensive car e patients (n = 8) and patients undergoing gastroscopy (n = 8) or colo noscopy (n = 8). NO concentrations were measured by chemolumininescenc e detection in air obtained through a nasogastric tube, after inflatio n into the stomach of a defined volume of air, or directly in the air suctioned from the endoscope. The mean NO concentration obtained from the stomach of healthy volunteers studied under baseline conditions wa s 18.0 +/- 2.8 (SEM) p.p.m. Day-to-day reproducibility of NO measureme nts was high. Tube feeding with a nitrite-and nitrate-free feeding sol ution left gastric NO concentrations unchanged, but standardized bicyc le exercise caused an approximate to 30% decrease in NO levels. NO con centrations in intensive care patients were approximate to 2 log cycle s lower than in healthy volunteers. NO levels in the colon were simila r to those in the stomach. We have described two readily applicable te chniques for diner, uncontaminated measurement of NO concentrations in the lumen of the gastrointestinal tract. Our finding of a striking re duction in gastric NO concentrations in intensive care patients requir es further study.