Cyclooxygenase inhibition with indomethacin increases human duodenal mucosal response to prostaglandin E1

Muscularis mucosae contraction evokes colonic secretion via prostaglandin synthesis and nerve stimulation

This in vitro study tested the hypothesis that muscularis mucosae contractile activity contributes to rabbit colonic mucosal function by mechanisms other than simple mechanical deformation of the epithelium. Experiments were performed by using a technique that allows simultaneous recording of muscle activity and transmucosal potential difference, a measure of epithelial ion transport. ATP, bradykinin, histamine, PGE(2), PGF(1alpha), and PGF(2alpha) elicited muscularis mucosae contractions that were resistant to atropine and TTX. Only ATP-induced contractions were indomethacin sensitive, and only those to dimethylphenylpiperazinium iodide (DMPP) were reduced by atropine. All agonist-evoked increases in transmucosal potential difference were atropine resistant, and, with the exception of those to PGE(2), PGF(2alpha), and VIP, they were also TTX sensitive. Mucosal responses to ATP, bradykinin, and histamine were indomethacin sensitive, whereas those to DMPP, the prostaglandins, and VIP were not. When cyclooxygenase activity or the mucosal innervation was compromised, even maximal muscularis mucosae contractions did not produce large secretory responses. It is concluded that contraction-related prostaglandin synthesis and noncholinergic secretomotor neuron stimulation represent the physiological transduction mechanism through which muscularis mucosae motor activity is translated into mucosal secretion.

Neurohormonal mechanisms of cigarette smoke-induced duodenal mucosal bicarbonate secretion in the rat

The effect of cigarette smoke and nicotine on duodenal mucosal bicarbonate secretion (DMBS) was studied in rats. Cigarette smoke but not intravenous nicotine administered acutely to anesthetized rats via a tracheostomy tube stimulated DMBS by 47 +/- 6%. The increase was neurally mediated via atropine-sensitive postganglionic cholinergic neurons. Introduction of cigarette smoke after the infusion of vasoactive intestinal peptide and porcine histidine isoleucine (PHI) also caused a delayed increase in DMBS. However, the magnitude of this increase was similar to that seen in control non-peptide-infused rats. The increase in bicarbonate secretion predominantly involved Brunner's glands. Rats exposed to cigarette smoke for 4 and 8 days before direct instillation of smoke via tracheostomy tube did not show any increase in their DMBS. These studies indicate that in the rat, cigarette smoke increases DMBS, most likely secreted by the Brunner's glands. The increase is neurally mediated via atropine-sensitive postganglionic cholinergic neurons. Gastroenteric neuropeptides do not exert any influence on cigarette smoke-mediated DMBS secretion in the rat. Unlike acute exposure to cigarette smoke, chronic exposure (4 and 8 days) of rats to cigarette smoke abolishes increase in DMBS induced by subsequent exposure to cigarette smoke. This last observation may, in part, may explain the tendency of chronic smokers who have duodenal bulb ulcers to show greater propensity to higher rate of recurrence and protracted healing.

Induction of alkalinization in cultured renal cells (MDCK line) by prostaglandin E2

The effect of prostaglandin E2 (PGE2), on the intracellular pH (pHi) in BCECF-loaded Madin Darby Canine Kidney (MDCK) cells was investigated. PGE2 elevated the pHi. Under resting conditions, pHi of MDCK cells suspended in PBS at pH 7.4 was 7.11 +/- 0.08; PGE2 increased pHi with an EC50 of 0.16 microM. PGF2 alpha elicited a similar response to PGE2, with an EC50 of 0.24 microM. Amiloride (0.4 mM) reversed the response to PGE2 (control 7.18 +/- 0.05; PGE2 7.26 +/- 0.05; after amiloride 7.18 +/- 0.05). In MDCK cells exposed to a Na(+)-free solution, alkalinization induced by this eicosanoid was blocked (Ringer-choline 7.16 +/- 0.03; PGE2 7.16 +/- 0.02). PGE2 increased by 100% the rate of recovery after an acidification pulse with ammonium chloride. In the presence of Ringer-HCO3- (pH 7.4), there was a delay in the maximal response to this prostaglandin (PBS 2.2 +/- 0.27, Ringer-bicarbonate 3.4 +/- 0.55 min) and the pHi increment was less marked than in PBS (0.09 pH units in HCO3- versus 0.16 pH units in PBS; P < 0.001). This effect of PGE2 was not blocked by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (1.0 mM). PMA (100 nM), activator of protein kinase C, mimicked the response to PGE2, suggesting the participation of this kinase on the effect of the prostanoid. As expected, two inhibitors of protein kinase C, staurosporine and sphingosine, abolished the response to PGE2. Staurosporine (0.10 microM), an inhibitor of protein kinase C, blocked the response to PGE2 (control 7.02 +/- 0.04; PGE2 and staurosporine 7.03 +/- 0.04, n = 9, not significant). Sphingosine, another inhibitor of protein kinase C, also blocked the response to PGE2. Two analogues of cAMP did not modify the pHi. In summary, PGE2 induced an intracellular alkalinization via stimulation of a Na+/H+ exchanger, with the participation of protein kinase C, in MDCK cells.

Theophylline and prostaglandin E2 on duodenal bicarbonate secretion: role for 5'-cyclic adenosine monophosphate

Cyclic adenosine monophosphate (cAMP) has been implicated as an intracellular "second" messenger in duodenal mucosal bicarbonate secretion in animals. The purpose of this study was to determine whether cAMP may mediate duodenal mucosal bicarbonate secretion in humans. In healthy volunteers, a 4-cm segment of proximal duodenum was isolated from gastric and pancreaticobiliary secretions. Either the phosphodiesterase inhibitor theophylline, prostaglandin (PG) E2, or a combination thereof was administered topically to the isolated duodenal mucosa. Theophylline (10(-2) mol/L) and PGE2 (10(-5)-10(-4) mol/L) each significantly increased bicarbonate secretion and transmucosal potential difference. Moreover, when theophylline and PGE2 were administered in combination, the duodenal bicarbonate output was additive compared to either agent alone. When theophylline was infused with increasing doses of PGE2, the dose-response curve was shifted to the left. Furthermore, increases in bicarbonate secretion and transmucosal potential difference were correlated significantly. These results suggest that cAMP may act as an intracellular mediator of human duodenal mucosal bicarbonate secretion.

Helicobacter pylori-negative duodenal ulcer

PURPOSE PATIENTS AND METHODS: Helicobacter pylori (HP) is present in more than 90% of duodenal ulcers (DUs). To investigate the pathophysiology in those patients with DU who are HP-negative compared with those who are HP-positive, we interviewed consecutive patients prior to endoscopy regarding factors often associated with ulcer disease. At esophagogastroduodenoscopy, antral biopsy specimens were obtained for urease test, culture, and Warthin Starry staining for HP in all patients with DU who did not have active bleeding.

RESULTS

Compared with HP-positive patients who had DU, HP-negative patients with DU were more likely to be aspirin users and less likely to have had prior ulcers. HP-positive patients with DU had more severe antral inflammation than HP-negative patients. Whites were more likely to be HP-negative than blacks. HP-negative patients with DU most commonly presented with bleeding, whereas HP-positive patients with DU presented with pain.

CONCLUSIONS

Our findings suggest a different mechanism for DUs in patients who are HP-positive versus those who are HP-negative, and this difference might have a bearing on treatment. The absence of HP should lead to a more thorough search for nonsteroidal anti-inflammatory drug/aspirin use, Zollinger-Ellison syndrome, and other potential causes of DUs.

Cholinergic mechanisms involved in release and effect of prostaglandin E2 in HCl-stimulated duodenal HCO-3 secretion in the conscious rat

Using a proximal duodenal loop in conscious rats, we investigated interactions between prostaglandin E2 and nicotinic and muscarinic receptor mechanisms previously found to be involved in the duodenal HCO3- response to HCl. In previous studies using the same model, a 5-min perfusion of the duodenal loop with 150 mmol l-1 HCl produced a marked and sustained HCO3- response. In the present study, the identical challenge produced a rapid 20-fold increase in the luminal output of prostaglandin E2 during acid exposure, followed by a sustained more than twofold elevation above the basal level during the 45 min monitored. The prostaglandin synthesis inhibitor indomethacin (4 mg kg-1 i.p.) suppressed the output of prostaglandin E2 during the HCl challenge from 131 +/- 84 to 15.4 +/- 10.0 pmol cm-1 h-1, and in the post-stimulatory period from 17.3 +/- 9.1 to 4.4 +/- 2.2 pmol cm-1 h-1. The nicotinic receptor antagonist hexamethonium (20 mg kg-1 i.v.) had no effect on the output of prostaglandin E2. The muscarinic receptor antagonist atropine (0.5 mg kg-1 s.c.) had no effect on the output of prostaglandin E2 during HCl challenge, but reduced the post-stimulatory output to 7.7 +/- 4.1 pmol cm-1 h-1. Perfusion of the duodenal loop with 0.1 mmol l-1 prostaglandin E2 produced a HCO3- response that was abolished by hexamethonium (20 mg kg-1 i.v.), but not affected by atropine (0.5 mg kg-1 s.c.).(ABSTRACT TRUNCATED AT 250 WORDS)