Pharmacological regulation of gastric acid secretion in the apical membrane of parietal cells; a new target for antisecretory drugs.

We examined the local effect of several drugs against secretagogue-stimulated acid secretion in dogs. Test drugs were applied to denervated gastric pouches in conscious dogs either for 5 to 30 min beginning 1 hr after or for 30 min before intravenous infusion of gastric secretagogues (histamine, pentagastrin, or carbachol). The antisecretory effect of test drugs delivered by an intravenous or oral route was also examined. Local application of acid pump inhibitors (omeprazole, leminoprazole) for 30 min beginning 1 hr after histamine infusion significantly inhibited gastric acid secretion. The effect of leminoprazole persisted for more than 8 hr after a 30 min application. A mast cell stabilizer (FPL 52694) applied to pouches for 15 to 30 min also potently inhibited histamine-stimulated gastric acid secretion in a time-dependent manner. The duration of the antisecretory effect of such drugs after a 30 min application was greater than 4 hr. Locally applied leminoprazole and FPL 52694 for 30 min also significantly inhibited pentagastrin- and carbachol-stimulated gastric acid secretion. Although intravenous omeprazole and leminoprazole exerted a potent antisecretory effect on histamine-induced acid secretion FPL 52694 had little or no antisecretory effect following intravenous or oral administration. 16,16-dimethyl prostagladin E2 also locally inhibited histamine-stimulated acid secretion. Acid stable local anesthetics (tetracaine, ethyl-4-aminobenzoate), histamine H2-receptor blockers (cimetidine, ranitidine, and famotidine), and a muscarinic M1-receptor antagonist (pirenzepine) did not exhibit local antisecretory effects. Such results strongly suggest that the apical membrane of parietal cells possesses a pharmcologically sensitive portion similar to the basolateral membrane, which usually mediates gastric acid secretion. The apical membrane represents an intriguing target for new antisecretory drugs, as well as a new medium for further elucidating the functional features of parietal cells.

Development of a sensitive enzyme-linked immunosorbent assay for eotaxin and measurement of its levels in human blood.

The CC chemokine eotaxin is potent eosinophil-selective chemoattractant, and it is thought that the function of eotaxin is closely related to the recruitment of eosinophils in certain inflammatory reactions. In order to learn more about the biological role of this molecule, we have developed a new sandwich ELISA method to measure human eotaxin using two monoclonal anitibodies and purified recombinant eotaxin as a standard. The minimal detectable concentration of eotaxin in this assay was 1.5 pg/ml, and the working range was 3.1--200 pg/ml with low CVs (< 10%). Both within- and between-run precision levels were less than 6.7% of the CVs. The dilution curves of two serum and two spiked plasma samples showed good linearity and the recovery range was 92.8--103.3%. No cross-reactivity was found with other similar chemokines. MCP-1, MCP-2, MCP-3, MCP-4, eotaxin-2 and RANTES. This assay was sensitive enough to measure the circulating eotaxin levels of healthy volunteers. However, the eotaxin levels in serum samples (mean+/-SD; 68.6+/-13.4 pg/ml, n=15) were significantly higher than those in matched plasma samples (19.2+/-5.4 pg/ml) separated from blood collected in tubes containing EDTA. Kinetic studies revealed that the eotaxin levels in serum markedly increased depending on the elapsed time before separation from blood cells, but such changes in EDTA-plasma were negligible up to 4 h at 25 degrees C. Our new ELISA is an accurate and useful method for quantifying human eotaxin in blood and demonstrates that the process of preparing blood samples affects the measurement of the eotaxin levels.

Antisecretory effect of leminoprazole on histamine-stimulated gastric acid secretion in dogs: potent local effect.

Leminoprazole, an acid pump inhibitor, significantly reduces basal and stimulated gastric acid secretion in rats when administered via the systemic or local route. Our aim here was to characterize the antisecretory effect of leminoprazole on gastric acid secretion in conscious dogs. Gastric acid secretion by dogs with a vagally denervated Heidenhain pouch was stimulated by intravenous histamine infusion. Leminoprazole or omeprazole (as a reference drug) was administered either intravenously or locally into the pouch before or after histamine infusion. A bolus intravenous administration of leminoprazole and omeprazole, respectively, significantly and dose-relatedly inhibited the stimulated gastric acid secretion for > 26 hr. Local application of leminoprazole, but not omeprazole, significantly inhibited the acid secretion when applied for 15 to 30 min. The duration of the local antisecretory effect observed after 30 min application was around 8-10 hr. The acid-degraded products of leminoprazole had no effect when applied to the pouch. The blood concentration of leminoprazole was very low at 1 hr after local application. These results indicate that leminoprazole suppresses the secretory function of the parietal cells of dogs, via both the intravenous and local routes. It remains unknown whether or not locally applied leminoprazole produced the acid inhibition by inhibiting the acid pump.

Effects of a new histamine H2-receptor antagonist, Z-300, on gastric secretion and gastro-duodenal lesions in rats: comparison with roxatidine.

We examined the effects of a new compound, N-[3-[3-(piperidinomethyl)phenoxy]-propyl]-2-(2-hydroxyethyl-1- thio)acetamido.2-(4-hydroxy benzoyl)benzoate (Z-300), on the histamine H2-receptor, gastric secretion in rats and dogs, and acute gastro-duodenal lesions or chronic gastric ulcers in rats. Roxatidine acetate hydrochloride (roxatidine), a known histamine H2-receptor antagonist, was used as a reference compound. The pA2 values for Z-300 and roxatidine for the isolated guinea pig atrium were 6.8 and 7.0, respectively. These agents at less than 10(-5) M did not affect the contraction of guinea pig ileum in response to carbachol. Z-300, administered either orally or parenterally, significantly inhibited the basal and histamine-stimulated gastric acid secretion in rats. Gastric acid secretion stimulated by histamine, pentagastrin or carbachol in Heidenhain pouch dogs was also significantly inhibited by the compound. The effect persisted for greater than 7 hr in the case of histamine-stimulation. Oral Z-300 significantly protected the gastric mucosa from water-immersion stress-, indomethacin-, aspirin- and HCl.ethanol-induced lesions and protected the duodenal mucosa against mepirizole- and cysteamine-induced ulcers. These effects on gastric secretion and lesion formation were, as a whole, stronger than those observed with roxatidine. Z-300, but not roxatidine, significantly accelerated the spontaneous healing of acetic acid ulcers induced in rats and prevented the delay in ulcer healing caused by indomethacin. The mechanism of action of Z-300 on acute lesions and chronic ulcers appears to be mostly related to its potent antisecretory and mucosal-protective activities.