Modification of 5-hydroxytryptophan-evoked 5-hydroxytryptamine formation of guinea pig colonic mucosa by reactive oxygen species.
We studied whether reactive oxygen species (ROS) generated by normal colonic mucosa affect 5-hydroxytryptophan (5-HTP)-evoked 5-HT formation (measured as the sum of 5-HT plus 5-hydroxyindole acetic acid (5-HIAA) accumulation) of guinea pig's isolated colonic mucosa. Catalase (3000-6000 U/ml), a hydrogen peroxide (H2O2) scavenger or diphenylene iodonium (DPI, 10-100 microM), an NADPH oxidase inhibitor, concentration-dependently caused an increase of the sum of 5-HT plus 5-HIAA accumulation in the presence of 5-HTP (10 microM), but these drugs did not significantly affect the 5-HT-metabolite in the colonic mucosa measured as the ratio of 5-HIAA/5-HT. Exogenously applied H2O2 (10-100 microM) concentration-dependently inhibited the sum of 5-HT plus 5-HIAA accumulation. In contrast, neither superoxide dismutase (SOD, 100-300 U/ml), superoxide anion scavenger, nor dimetyl sulfoxide (1-5%, DMSO), a hydroxyl radical scavenger affected the sum of 5-HT plus 5-HIAA accumulation. Moreover, mucosa ROS generation was estimated using the chemiluminescence technique. SOD (100-300 U/ml), catalase (3000-6000 U/ml) or DPI (10-100 microM), concentration-dependently reduced luminol-enhanced chemiluminescence signal from the colonic mucosa, while allopurinol (10-100 microM), a xanthine oxidase inhibitor, did not affect the chemiluminescence signal. These results suggest that ROS is formed through an NADPH oxidase system in the guinea pig colonic mucosa, where it exerts a modulatory effect on mucosal 5-HT formation upon addition of 5-HTP. Thus, ROS formation from normal colonic mucosa could be considered to contribute to the control of 5-HT production in mucosa enterochromaffin cells.
Kojim
Shu-ichi
S
Department of Pharmacology, Dokkyo University School of Medicine, Mibu, Tochigi, Japan. s-kojima@dokkyomed.ac.jp
Ikeda
Masashi
M
Shibukawa
Asako
A
Kamikawa
Yuichiro
Y
D006916:5-Hydroxytryptophan / Q000494:pharmacology*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002374:Catalase / Q000494:pharmacology; D003106:Colon / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D004759:Enterochromaffin Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology; D006168:Guinea Pigs; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D008163:Luminescent Measurements; D008297:Male; D019255:NADPH Oxidases / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012701:Serotonin / Q000096:biosynthesis*
D000975:Antioxidants; D016166:Free Radical Scavengers; D009861:Onium Compounds; D017382:Reactive Oxygen Species; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; C007517:diphenyleneiodonium; D006916:5-Hydroxytryptophan; D002374:Catalase; D019255:NADPH Oxidases