Drugs online research references
J Biol Chem. 1985 Apr 25;260(8):4591-7.
Omeprazole, a specific inhibitor of gastric (H+-K+)-ATPase, is a H+-activated oxidizing agent of sulfhydryl groups.
Im WB, Sih JC, Blakeman DP, McGrath JP.
Omeprazole (5-methoxy-2-[[(4-methoxy-3,5- dimethylpyridinyl)methyl]sulfinyl]-1H-benzimidazole) appeared to inhibit gastric (H+-K+)-ATPase by oxidizing its essential sulfhydryl groups, since the gastric ATPase inactivated by the drug in vivo or in vitro recovered its K+-dependent ATP hydrolyzing activity upon incubation with mercaptoethanol. Biological reducing agents like cysteine or glutathione, however, were unable to reverse the inhibitory effect of omeprazole. Moreover, acidic environments enhanced the potency of omeprazole. For example, in vivo pretreatment of rats with carbachol, a secretagogue, enhanced the activity of omeprazole to inhibit gastric (H+-K+)-ATPase, while pretreatment with cimetidine, an antisecretory agent, reduced its potency. In vitro, lowering pH of incubation media from 7.4 to 5.0 improved the ability of omeprazole to inhibit hog gastric (H+-K+)-ATPase almost 60-fold. The inhibitory effect of the drug was accompanied by a dose-dependently decreased amount of free sulfhydryl groups in the isolated hog gastric membranes. The chemical reactivity of omeprazole with mercaptans is also consistent with the biological action of omeprazole. The drug, only under acidic conditions, reacted with a stoichiometric amount of ethyl mercaptan (or beta-mercaptoethanol) to produce regio-isomers of N-sulfenylated omeprazole sulfide (5-methoxy-2[[(4-methoxy-3,5- dimethyl-2-pyridinyl)methyl]thio]-1- or 3-(ethylthio)benzimidazole). The N-sulfenylated compound reacted at neutral pH with another stoichiometric amount of ethyl mercaptan to produce omeprazole sulfide quantitatively. The gastric polypeptides of 100 kilodaltons representing (H+-K+)-ATPase in the rat gastric mucosa or isolated hog gastric membranes were covalently labeled with [14C]omeprazole. The radioactive label bound to the ATPase, however, could not be displaced by mercaptoethanol under the identical conditions where the ATPase activity was fully restored. These observations suggest that the essential sulfhydryl groups which reacted with omeprazole did not form a stable covalent bond with the drug, but rather that they further reacted with adjacent sulfhydryl groups to form disulfides which could be reduced by mercaptoethanol.
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Masui. 1994 Mar;43(3):369-73.
[A gastric proton pump inhibitor as preanesthetic medication]
[Article in Japanese]
Murakawa T, Kudo A, Kubota T, Hashimoto Y, Takagi Y, Taguchi S, Matsuki A.
Department of Anesthesiology, Odate Municipal Hospital.
Effect of omeprazole, a gastric proton pump inhibitor, on gastric secretion during anesthesia and surgery was evaluated in 39 elective surgical patients ranged in age from 18 to 69 years. These patients were divided into two groups according to their age either of 40 years and under or over. The patients of both groups underwent orthopedic, ophthalmic, ENT, plastic, oral or non-abdominal surgery under neuroleptanesthesia, enflurane anesthesia or total intravenous anesthesia with droperidol, fentanyl and ketamine. They all were administered omeprazole 20 mg orally at 21:00 the night before surgery and again at 7:00 on the morning of surgery. The volume and acidity of gastric juice were measured at anesthetic induction and emergence from anesthesia. The volume and pH of the gastric juice in patients of 40 years and under in age averaged to 9.8 +/- 3.2 (mean +/- SE) ml, 2.45 +/- 0.56 at the anesthetic induction and 9.3 +/- 4.1 ml, 4.66 +/- 0.60 at the emergence from anesthesia respectively. The mean volume and pH of the gastric juice in patients over 40 years of age were 5.0 +/- 1.7 ml, 4.68 +/- 0.56 at the anesthetic induction and 9.9 +/- 2.4 ml, 5.76 +/- 0.36 at the emergence from anesthesia respectively. Significant decrease in the volume and acidity of gastric juice was observed in the patients of both groups except that the average of intragastric pH of the patients under 40 years of age was below 2.50 at the induction of anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)
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niftyserve.or.jp
The effects of proton pump inhibitors on thyroid hormone metabolism in rats were examined. Pantoprazole, omeprazole, and lansoprazole were administered repeatedly to female SD rats at doses of 5, 50, and 300 mg/kg/day for 1 week, and changes in UDP-glucuronyltransferase activities were examined. Increases in o-aminophenol UDP-glucuronyltransferase activity, which was measured as that responsible for the glucuronidation of thyroxine, were evident following 7-day high-dose administration of all the proton pump inhibitors tested. Of the three proton pump inhibitors investigated, o-aminophenol UDP-glucuronyltransferase activity was greatest following the high-dose administration of omeprazole. Androsterone UDP-glucuronyltransferase activity in rats treated with the proton pump inhibitors increased significantly, but these increases were smaller than those of o-aminophenol UDP-glucuronyltransferase. Pantoprazole and omeprazole treatment did not affect plasma T4 or T3 significantly, whereas lansoprazole treatment produced marked reductions in plasma T4 but did not affect plasma T3 significantly. After administration of 125I-labeled thyroid hormone to rats treated with the proton pump inhibitors, biliary excretion of radioactivity increased significantly in omeprazole- and lansoprazole-treated rats; these increases were attributed to induction of liver thyroxine UDP-glucuronyltransferase activities. The order of biliary excretion of radioactivity, as well as the o-aminophenol UDP-glucuronyltransferase activity, in the treated animals was: omeprazole > lansoprazole > pantoprazole. Therefore, repeated administration of the proton pump inhibitors increased thyroxine-metabolizing activity via induction of UDP-glucuronyltransferase, and this induction by pantoprazole was less pronounced than that by omeprazole or lansoprazole.
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