title: Gastrointestinal nitric oxide generation in germ-free and conventional rats.
abstract: Nitric oxide (NO) is a central mediator of various physiological events in the gastrointestinal tract. The influence of the intestinal microflora for NO production in the gut is unknown. Bacteria could contribute to this production either by stimulating the mucosa to produce NO, or they could generate NO themselves. Using germ-free and conventional rats, we measured gaseous NO directly in the gastrointestinal tract and from the luminal contents using a chemiluminescence technique. Mucosal NO production was studied by using an NO synthase (NOS) inhibitor, and to evaluate microbial contribution to the NO generation, nitrate was given to the animals. In conventional rats, luminal NO differed profoundly along the gastrointestinal tract with the greatest concentrations in the stomach [>4,000 parts per billion (ppb)] and cecum (approximately 200 ppb) and lower concentrations in the small intestine and colon (< or =20 ppb). Cecal NO correlated with the levels in incubated luminal contents. NOS inhibition lowered NO levels in the colon, without affecting NO in the stomach and in the cecum. Gastric NO increased greatly after a nitrate load, proving it to be a substrate for NO generation. In germ-free rats, NO was low (< or =30 ppb) throughout the gastrointestinal tract and absent in the incubated luminal contents. NO also remained low after a nitrate load. Our results demonstrate a pivotal role of the intestinal microflora in gastrointestinal NO generation. Distinctly compartmentalized qualitative and quantitative NO levels in conventional and germ-free rats reflect complex host microbial cross talks, possibly making NO a regulator of the intestinal eco system.
authors.affiliation: Centre for Allergy Research, Karolinska Institutet, S-17177 Stockholm, Sweden. tanja.sobko@fyfa.ki.se
authors.forename: Tanja
authors.initials: T
authors.lastname: Sobko
authors.forename: Claudia
authors.initials: C
authors.lastname: Reinders
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Norin
authors.forename: Tore
authors.initials: T
authors.lastname: Midtvedt
authors.forename: Lars E
authors.initials: LE
authors.lastname: Gustafsson
authors.forename: Jon O
authors.initials: JO
authors.lastname: Lundberg
mesh_terms: D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005766:Gastrointestinal Contents / Q000737:chemistry; D041981:Gastrointestinal Tract / Q000378:metabolism*; D005856:Germ-Free Life / Q000502:physiology*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009566:Nitrates / Q000032:analysis / Q000494:pharmacology; D009569:Nitric Oxide / Q000032:analysis / Q000096:biosynthesis*; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D004791:Enzyme Inhibitors; D009566:Nitrates; D009569:Nitric Oxide; C031618:sodium nitrate; D019331:NG-Nitroarginine Methyl Ester