4-acetamido-4--isothiocyanatostilbene-2-2--disulfonic-acid and Stomach-Ulcer

The effect of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of Cl(-)-HCO3- exchanger, on stress-induced gastric lesions was studied in rats. The stress exposure to rats was performed by restraint plus water-immersion (22 degrees C) for 6 h. Oral administration of DIDS produced a dose-dependent reduction in the gastric lesion formation. The ED50 value for DIDS was 94.4 mg/kg (64.2 - 138.8 mg/kg; 95% confidence limits) and the maximum effect was observed at the dose of 300 mg/kg with an inhibition of 95%. A dose-dependent reduction in lesions was also observed after administration of omeprazole, an inhibitor of proton pump. The ED50 value for omeprazole was 3.1 mg/kg (1.8 - 5.4 mg/kg; 95% confidence limits) and the effect was maximum at 16 mg/kg with an inhibition of 92%. These results indicated that DIDS protected the gastric mucosa against stress-induced lesions. It is speculated that the antiulcerous activity of DIDS may give a clue for the development of a new class of therapeutic drugs for the prevention and healing of gastric ulcers.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Animals; Carrier Proteins; Chloride-Bicarbonate Antiporters; Immersion; Male; Omeprazole; Rats; Rats, Wistar; Restraint, Physical; Stomach Ulcer; Stress, Psychological

Intracellular pH (pHi) was measured with proton-sensitive liquid sensor microelectrodes in isolated Necturus antral mucosa, paying special attention to arranging experimental conditions to simulate conditions frequently associated with in vivo "stress ulceration." Intracellular pH in mucosas perfused under standard conditions (Ringer's solution containing HCO3-/CO2) was 7.22 + 0.02 (n = 27). Removal of Na+ and HCO3- or addition of amiloride or 4-acetamido-4-isothiocyanostillbene-2,2-disulfonic acid (blockers of Na+/H+ and Cl-/HCO3-exchangers) had no influence on steady-state pHi, suggesting that these ion exchangers do not significantly contribute to the maintenance of pHi in the presence of normal external pH. Acidification of mucosal (luminal) perfusate to pH 3 (mimicking the presence of gastric acid) had no influence on pHi, but mucosal pH 2 (10 mM HCl) acidified pHi to 6.93 +/- 0.07. Acidification of serosal (nutrient) perfusate to pH 6 (mimicking intramucosal acidosis caused by back-diffusion of luminal H+) acidified pHi to 6.72 +/- 0.10. Removal of Na+ from and addition of amiloride to the serosal perfusate during exposure to serosal pH 6.0 induced further acidification of pHi, suggesting that in this acidotic situation (with very low ambient HCO3- concentration) a Na+/H+ exchanger does contribute to the maintenance of steady-state pHi. Increased PCO2 (10% vol/vol in the gas) in a slightly acidic milieu (mimicking mucosal ischemia) likewise acidified pHi to 6.73 +/- 0.05. A combination of mucosal acid (pH 3), high PCO2 (10% CO2), and low serosal pH (pH 6) (mimicking conditions that prevail, for example, during hemorrhagic shock) acidified pHi and ultimately resulted in cell death. These derangements of intracellular acid-base balance may have pathogenetic importance also in in vivo stress ulceration.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; Amiloride; Animals; Carbonates; Gastric Mucosa; Hydrogen-Ion Concentration; Isotonic Solutions; Membrane Potentials; Microelectrodes; Necturus; Pyloric Antrum; Ringer's Solution; Sodium; Stomach Ulcer; Stress, Physiological

The relationship between mucosal protection by ambient HCO3- and its impact on intracellular pH was studied in isolated frog gastric mucosa. Closed sacs of gastric mucosa, containing exogenous HCl and pepsin, readily ulcerated when incubated in Ringer solution devoid of HCO3-, but were effectively protected against ulceration when ambient HCO3- was present. This protection was abolished by blocking anion exchange in cell membrane by 4-acetamido-4'-isothiocyanostillbene-2,2'-disulfonic acid or by inhibiting mucosal carbonic anhydrase by azetazolamide. Intracellular pH, measured by the 14C-labeled 5,5-dimethylxazolidine-2,4-dione method, was significantly higher when open sheets of mucosas were incubated in a medium containing HCO3- than when they were incubated in a medium devoid of HCO3- at the same external pH. Furthermore, a positive pH gradient across the cell membrane (intracellular pH was greater than extracellular pH) was generated only if HCO3- was present in the incubation medium. 4-Acetamido-4'-isothiocyano-stillbene-2,2'-disulfonic acid completely abolished these effects of ambient HCO3- on intracellular pH, suggesting that ambient HCO3- contributes to intracellular pH by acting as an intracellular base. In contrast, acetazolamide had no significant influence on these effects, suggesting that carbonic anhydrase acts in the protective mechanism distally to the entry of HCO3- into the cell. The data indicate that ambient HCO3- significantly contributes to intracellular pH in the gastric mucosa, a feature that may enhance the ability of the mucosa to withstand intraluminal acid.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; Acetazolamide; Animals; Bicarbonates; Carbon Dioxide; Gastric Mucosa; HEPES; Hydrochloric Acid; Hydrogen-Ion Concentration; Pepsin A; Rana temporaria; Stomach Ulcer