Contribution of endogenous nitrergic and peptidergic influences to the altered neurally-induced gastric contractile responses in strips from dystrophic (mdx) mice

Presence and Effects of Pituitary Adenylate Cyclase Activating Polypeptide Under Physiological and Pathological Conditions in the Stomach

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide with widespread occurrence throughout the body including the gastrointestinal system. In the small and large intestine, effects of PACAP on cell proliferation, secretion, motility, gut immunology and blood flow, as well as its importance in bowel inflammatory reactions and cancer development have been shown and reviewed earlier. However, no current review is available on the actions of PACAP in the stomach in spite of numerous data published on the gastric presence and actions of the peptide. Therefore, the aim of the present review is to summarize currently available data on the distribution and effects of PACAP in the stomach. We review data on the localization of PACAP and its receptors in the stomach wall of various mammalian and non-mammalian species, we then give an overview on PACAP's effects on secretion of gastric acid and various hormones. Effects on cell proliferation, differentiation, blood flow and gastric motility are also reviewed. Finally, we outline PACAP's involvement and changes in various human pathological conditions.

Glucagon-like peptide-2 modulates the nitrergic neurotransmission in strips from the mouse gastric fundus

AIM

To investigate whether glucagon-like peptide-2 (GLP-2) influences the neurally-induced responses in gastric strips from mice, since no data are available.

METHODS

For functional experiments, gastric fundal strips were mounted in organ baths containing Krebs-Henseleit solution. Mechanical responses were recorded via force-displacement transducers, which were coupled to a polygraph for continuous recording of isometric tension. Electrical field stimulation (EFS) was applied via two platinum wire rings through which the preparation was threaded. The effects of GLP-2 (2 and 20 nmol/L) were evaluated on the neurally-induced contractile and relaxant responses elicited by EFS. Neuronal nitric oxide synthase (nNOS) enzyme was evaluated by immunohistochemistry.

RESULTS

In the functional experiments, electrical field stimulation (EFS, 4-16 Hz) induced tetrodotoxin (TTX)-sensitive contractile responses, which were reduced in amplitude by GLP-2 (P < 0.05). In the presence of the nitric oxide (NO) synthesis inhibitor L-NNA, GLP-2 no longer influenced the neurally-evoked contractile responses (P > 0.05). The direct smooth muscle response to methacholine was not influenced by GLP-2 (P > 0.05). In the presence of guanethidine and carbachol, the addition of GLP-2 to the bath medium evoked TTX-sensitive relaxant responses that were unaffected by L-NNA (P > 0.05). EFS induced a fast NO-mediated relaxation, whose amplitude was enhanced in the presence of the hormone (P < 0.05). Immunohistochemical experiments showed a significant increase (P < 0.05) in nNOS immunoreactivity in the nerve structures after GLP-2 exposure.

CONCLUSION

The results demonstrate that in gastric fundal strips, GLP-2 influences the amplitude of neurally-induced responses through the modulation of the nitrergic neurotransmission and increases nNOS expression.

Glucagon-like peptide 2 counteracts the mucosal damage and the neuropathy induced by chronic treatment with cisplatin in the mouse gastric fundus

BACKGROUND

Glucagon-like peptide-2 (GLP-2) is a pleiotropic hormone synthesized and secreted by the enteroendocrine 'L' cells able to exert intestine-trophic and anti-inflammatory effects. The antineoplastic drug cisplatin causes gastrointestinal alterations with clinical symptoms (nausea and vomiting) that greatly affect the therapy compliance. Experimentally, it has been reported that chronic cisplatin treatment caused mucosal damage and enteric neuropathy in the rat colon.

METHODS

We investigated, through a combined immunohistochemical and functional approach, whether [Gly(2) ]GLP-2, a GLP-2 analog, was able to counteract the detrimental effects of long-term cisplatin administration in the mucosa and myenteric neurons of mouse gastric fundus.

KEY RESULTS

Morphological experiments showed a reduction in the epithelium thickness in cisplatin-treated mice, which was prevented by [Gly(2) ]GLP-2 co-treatment. Immunohistochemistry demonstrated that cisplatin caused a significant decrease in myenteric neurons, mainly those expressing neuronal nitric oxide synthase (nNOS), that was prevented by [Gly(2) ]GLP-2 co-treatment. In the functional experiments, [Gly(2) ]GLP-2 co-treatment counteracted the increase in amplitude of the neurally induced contractions observed in strips from cisplatin-treated animals. The NO synthesis inhibitor L-N(G) -nitro arginine caused an increase in amplitude of the contractile responses that was greater in preparations from cisplatin+[Gly(2) ]GLP-2 treated mice compared to the cisplatin-treated ones.

CONCLUSIONS & INFERENCES

The results demonstrate that in cisplatin long-term treated mice [Gly(2) ]GLP-2 is able to counteract both the mucosal gastric fundus damage, by preventing the epithelium thickness decrease, and the neuropathy, by protecting the nNOS neurons. Taken together, the present data suggest that [Gly(2) ]GLP-2 could represent an effective strategy to overcome the distressing gastrointestinal symptoms present during the anti-neoplastic therapy.

Influence of obestatin on the gastric longitudinal smooth muscle from mice: mechanical and electrophysiological studies

Obestatin is a hormone released from the stomach deriving from the same peptide precursor as ghrelin. It is known to act as an anorectic hormone decreasing food intake, but contrasting results have been reported about the effects of obestatin on gastrointestinal motility. The aim of the present study was to investigate whether this peptide may act on the gastric longitudinal smooth muscle by using a combined mechanical and electrophysiological approach. When fundal strips from mice were mounted in organ baths for isometric recording of the mechanical activity, obestatin caused a tetrodotoxin-insensitive decrease of the basal tension and a reduction in amplitude of the neurally induced cholinergic contractile responses, even in the presence of the nitric oxide synthesis inhibitor N(G)-nitro-l-arginine. Obestatin reduced the amplitude of the response to the ganglionic stimulating agent dimethylphenyl piperazinium iodide but did not influence that to methacholine. In nonadrenergic, noncholinergic conditions, obestatin still decreased the basal tension of the preparations without influencing the neurally induced relaxant responses. For comparison, in circular fundal strips, obestatin had no effects. Notably, in the longitudinal antral ones, obestatin only caused a decrease of the basal tension. Electrophysiological experiments, performed by a single microelectrode inserted in a gastric longitudinal smooth muscle cell, showed that obestatin had similar effects in fundal and antral preparations: it decreased the resting specific membrane conductance, inhibited Ca(2+) currents, and positively shifted their voltage threshold of activation. In conclusion, the present results indicate that obestatin influences gastric smooth muscle exerting site-specific effects.

Endocannabinoids modulate non-adrenergic, non-cholinergic inhibitory neurotransmission in strips from the mouse gastric fundus

AIM

To investigate the effects of endocannabinoids on non-adrenergic, non-cholinergic (NANC) relaxant responses in gastric strips from mice.

METHODS

Gastric longitudinal strips from the fundus region were mounted in organ baths for isometric recording.

RESULTS

In carbachol-precontracted strips, electrical field stimulation (EFS) elicited tetrodotoxin (TTX)-sensitive fast nitrergic relaxant responses that were followed, at the highest stimulation frequency, by sustained relaxations. The latter were abolished by α-chymotrypsin. Anandamide caused a TTX-sensitive relaxation that was abolished by α-chymotrypsin but unaffected by the nitric oxide (NO) synthesis inhibitor, Nω-nitro-L-arginine (L-NNA). Anandamide reduced the amplitude of EFS-induced fast relaxations, whereas increased that of sustained ones. Relaxation to the nicotinic receptor agonist dimethylphenyl piperazinium iodide (DMPP) was decreased in amplitude by either anandamide or L-NNA, whereas, surprisingly, it was increased by α-chymotrypsin and abolished by L-NNA plus α-chymotrypsin. Relaxation to vasoactive intestinal polypeptide (VIP) was not influenced by anandamide or L-NNA and was abolished by α-chymotrypsin. Following VIP desensitization, fast relaxant responses to EFS were reduced and the sustained ones abolished. The CB1 receptor antagonist AM251 increased, only at the highest stimulation frequency, the amplitude of the EFS-induced fast relaxation and reduced the sustained one. AM251 increased the response to DMPP and abolished that to anandamide. The CB2 receptor antagonist AM630 had no effects.

CONCLUSION

These results indicate that endocannabinoids modulate, via prejunctional CB1 receptors, the NANC peptidergic neurotransmission that, in turn, affects the nitrergic one.

Relaxin counteracts the altered gastric motility of dystrophic (mdx) mice: functional and immunohistochemical evidence for the involvement of nitric oxide

Impaired gastric motility ascribable to a defective nitric oxide (NO) production has been reported in dystrophic (mdx) mice. Since relaxin upregulates NO biosynthesis, its effects on the motor responses and NO synthase (NOS) expression in the gastric fundus of mdx mice were investigated. Mechanical responses of gastric strips were recorded via force displacement transducers. Evaluation of the three NOS isoforms was performed by immunohistochemistry and Western blot. Wild-type (WT) and mdx mice were distributed into three groups: untreated, relaxin pretreated, and vehicle pretreated. In strips from both untreated and vehicle-pretreated animals, electrical field stimulation (EFS) elicited contractile responses that were greater in mdx than in WT mice. In carbachol-precontracted strips, EFS induced fast relaxant responses that had a lower amplitude in mdx than in WT mice. Only in the mdx mice did relaxin depress the amplitude of the neurally induced excitatory responses and increase that of the inhibitory ones. In the presence of L-NNA, relaxin was ineffective. In relaxin-pretreated mdx mice, the amplitude of the EFS-induced contractile responses was decreased and that of the fast relaxant ones was increased compared with untreated mdx animals. Responses to methacholine or papaverine did not differ among preparations and were not influenced by relaxin. Immunohistochemistry and Western blotting showed a significant decrease in neuronal NOS expression and content in mdx compared with WT mice, which was recovered in the relaxin-pretreated mdx mice. The results suggest that relaxin is able to counteract the altered contractile and relaxant responses in the gastric fundus of mdx mice by upregulating nNOS expression.