Inducible nitric oxide synthase activity induced by sodium chloride solution prolongs luminal pH elevation in rat and mouse stomachs.
BACKGROUND
Sodium chloride (NaCl) is a strong promoter of gastric cancer. We hypothesized that inducible nitric oxide synthase (iNOS) induced by NaCl may be involved in its promoting effects. We investigated iNOS expression by hypertonic NaCl solutions and its pathophysiological roles in the gastric mucosa of rats and mice.


METHODS
iNOS mRNA and protein expressions were examined in the rat and mouse gastric mucosa after intragastric administration of NaCl solution by northern blot, reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. The effect on luminal pH by iNOS activity was assessed using aminoguanidine, a potent iNOS inhibitor, and iNOS gene deficient (iNOS-/-) mice.


RESULTS
iNOS expression was detected at concentrations higher than 1.7 M, mainly in the cells infiltrating the damaged mucosa of rats. Administration of a higher than 3.4 M NaCl solution elevated luminal pH of the rat stomach remarkably, enabling bacterial overgrowth and dramatically increasing iNOS expression (n = 5 per concentration). Pretreatment with ampicillin (p.o), an antibiotic, attenuated the iNOS expression in duplicate experiments. Co-treatment with aminoguanidine (s.q) accelerated recovery of elevated luminal pH at 8 h and 16 h or 24 h after administration of 3.4 M (n = 8) and 5.2 M NaCl solution (n = 5), respectively. iNOS expression and luminal pH elevation were also observed in mice stomachs after administration of 3.4 M NaCl solution. The elevated luminal pH of iNOS-/- mice stomachs after the administration of NaCl solution was significantly lower at 6 h (n = 7) and at 9 h (n = 11), compared to that of wild type mice (n = 9 and 10, respectively).


CONCLUSIONS
Hypertonic NaCl solutions induced iNOS expression in the gastric mucosa. iNOS activity prolonged the elevation of the luminal pH, potentially leading to bacterial overgrowth, which in turn enhanced iNOS expression. This vicious cycle might be related to the promoting effect of NaCl.
Tatemichi
Masayuki
M
Department of Environmental and Occupational Health, Toho University School of Medicine, Omorinishi Otaku, Tokyo, Japan.
Ogura
Tsutomu
T
Sakurazawa
Nobuyuki
N
Nagata
Hiroshi
H
Sugita
Minoru
M
Esumi
Hiroyasu
H
D000818:Animals; D001419:Bacteria / Q000254:growth & development; D005745:Gastric Acidity Determination; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D008297:Male; D051379:Mice; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D012965:Sodium Chloride / Q000494:pharmacology*; D012996:Solutions; D013270:Stomach / Q000187:drug effects* / Q000201:enzymology* / Q000382:microbiology; D013997:Time Factors
D012333:RNA, Messenger; D012996:Solutions; D012965:Sodium Chloride; D019001:Nitric Oxide Synthase