Constitutive NOS isoforms account for gastric mucosal NO overproduction in uremic rats

Helicobacter pylori status and esophagogastroduodenal mucosal lesions in patients with end-stage renal failure on maintenance hemodialysis

OBJECTIVES

The aim of this study was to elucidate the impact of Helicobacter pylori infection on esophagogastroduodenal mucosal lesions in patients with end-stage renal failure on maintenance hemodialysis (HD).

METHODS

An upper endoscopy and the (13)C-urea breath test were performed in 198 patients on maintenance HD. Clinical features, serum pepsinogen levels and esophagogastroduodenal mucosal lesions were compared between H. pylori-positive and H. pylori-negative patients. Risk factors associated with esophagogastroduodenal mucosal lesion were determined by multivariate analyses.

RESULTS

The upper endoscopy revealed that gastric erosion was the most frequent (58%) type of esophagogastroduodenal mucosal lesion, followed by duodenal erosion (18%), gastric ulcer (14%), gastroesophageal reflux disease (10%), and duodenal ulcer (7%). Of the 198 patients enrolled in the study, 81 were positive and 117 patients were negative for H. pylori infection. The time duration after the introduction of HD was significantly longer and serum pepsinogen I/II ratio was significantly higher in H. pylori-negative patients than in H. pylori-positive patients. Multivariate analyses revealed that the H. pylori infection was an independent, protective factor for gastric erosion (odds ratio 0.38; 95% confidence interval 0.21-0.70), while the infection was unrelated to other mucosal lesions.

CONCLUSIONS

The most common mucosal lesion observed in our study cohort, all of whom were patients on maintenance HD, was gastric erosion. The high prevalence of this type of lesion may be explained partly by the cure of H. pylori infection during the clinical course of maintenance HD.

Downregulation of nNOS and synthesis of PGs associated with endotoxin-induced delay in gastric emptying

A single intraperitoneal injection of endotoxin (40 microg/kg) significantly delayed gastric emptying of a solid nutrient meal. Blockade of nitric oxide synthase (NOS) with 30 mg/kg ip N(G)-nitro-L-arginine methyl ester or 20 mg/kg ip 7-nitroindazole [neuronal NOS (nNOS) inhibitor] significantly delayed gastric emptying in control animals but failed to modify gastric emptying in endotoxin-treated rats. Administration of 2.5, 5, and 10 mg/kg ip N(6)-iminoethyl-L-lysine [inducible NOS (iNOS) inhibitor] had no effect in either experimental group. Indomethacin (5 mg/kg sc), NS-398 (cyclooxygenase-2 inhibitor; 10 mg/kg ip), and dexamethasone (10 mg/kg sc) but not quinacrine (20 mg/kg ip) significantly prevented delay in gastric emptying induced by endotoxin but failed to modify gastric emptying in vehicle-treated animals. Ca(2+)-dependent NOS activity in the antrum pylorus of the stomach was diminished by endotoxin, whereas Ca(2+)-independent NOS activity was not changed. In addition, decreased nNOS mRNA and protein were observed in the antrum pylorus of endotoxin-treated rats. Our results suggest that downregulation of nNOS in the antrum pylorus of the stomach and synthesis of prostaglandins mediate the delay in gastric emptying of a solid nutrient meal induced by endotoxin.

Amphetamine increases the extracellular concentration of glutamate in striatum of the awake rat: involvement of high affinity transporter mechanisms

Using microdialysis it was found that intracerebral infusions of amphetamine increase the extracellular concentration of glutamate, and also of dopamine, aspartate, GABA, and taurine. The increases in glutamate produced by amphetamine was independent of calcium in the perfusion medium but was significantly attenuated by specific blockers of the high affinity transporters of this neurotransmitter. Amphetamine infusions also produced a decrease in the extracellular concentration of Na+, an increase in the extracellular concentration of lactate, and a decrease in haemoglobin in the area of perfusion. All these data suggest that amphetamine increases the extracellular concentration of glutamate and other neurotransmitters through a hypoxic mediated process. This study also shows that an alpha-noradrenergic receptor antagonist is able to attenuate the effects of amphetamine on the release of glutamate, dopamine, GABA and taurine, which further suggests a vasoconstrictor effect of amphetamine as a result of which hypoxia could develop.

Nitric oxide release in penile corpora cavernosa in a rat model of erection

1. Nitric oxide (NO) levels were measured in the corpus cavernosum of urethane-anaesthetized rats by using differential normal pulse voltammetry with carbon fibre microelectrodes coated with a polymeric porphyrin and a cation exchanger (Nafion). A NO oxidation peak could be recorded at 650 mV vs. a Ag-AgCl reference electrode every 100 s. 2. This NO signal was greatly decreased by the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), given by local and systemic routes, and enhanced by the NO precursor L-arginine. Treatment with L-arginine reversed the effect of L-NAME on the NO peak. 3. Both the NO signal and the intracavernosal pressure (ICP) were increased by electrical stimulation of cavernosal nerves (ESCN). However, the rise in the NO levels long outlived the rapid return to baseline of the ICP values at the end of nerve stimulation. 4. The ICP and the NO responses to ESCN were suppressed by local and systemic injections of L-NAME. Subsequent treatment with L-arginine of L-NAME-treated animals restored the NO signal to basal levels and the NO response to ESCN. The ICP response to ESCN was restored only in part by L-arginine. 5. The observed temporal dissociation between the NO and ICP responses could be accounted for by several factors, including the buffering of NO by the blood filling the cavernosal spaces during erection. 6. These findings indicate that an increased production of NO in the corpora cavernosa is necessary but not sufficient for maintaining penile erection and suggest a complex modulation of the NO-cGMP-cavernosal smooth muscle relaxation cascade.