vasoactive-intestinal-peptide and alpha-chymotrypsin

Glucagon-like peptide-2 (GLP-2) influences different aspects of the gastrointestinal function, including epithelial growth, digestion, absorption, motility, and blood flow. Intraluminal pressure from isolated mouse stomach was recorded to investigate whether GLP-2 affects gastric tone and to analyze its mechanism of action. Regional differences between diverse parts of the stomach were also examined using circular muscular strips from fundus and antrum. In the whole stomach, GLP-2 (0.3-100 nM) produced concentration-dependent relaxation with a maximum that was about 75% of relaxation to 1 microM isoproterenol (IC50=2.5 nM). This effect was virtually abolished by desensitization of GLP-2 receptors or by alpha-chymotrypsin. The relaxant response to GLP-2 was not affected by tetrodotoxin, a blocker of neuronal voltage-dependent Na+ channels, but it was significantly reduced by omega-conotoxin GVIA, a blocker of neuronal N-type voltage-operated Ca2+ channels. Nomega-nitro-L-arginine methyl ester, a blocker of nitric oxide synthase, or apamin, a blocker of Ca2+-dependent potassium channels, failed to affect the gastric response to the peptide. However, the relaxation was significantly antagonized by [Lys1,Pro2,5,Arg3,4,Tyr6]VIP7-28, a vasoactive intestinal peptide (VIP) receptor antagonist (GLP-2 maximum effect=45% of relaxation to 1 microM isoproterenol), and virtually abolished by desensitization of the VIP receptors. GLP-2 induced concentration-dependent relaxation in carbachol-precontracted fundic strips but not in antral strips. These results provide the first experimental evidence that GLP-2 is able to induce gastric relaxation acting peripherally on the mouse stomach. The effect appears to be mediated by prejunctional neural release of VIP and confined to fundic region.

Topics: Animals; Chymotrypsin; Enteric Nervous System; Enzyme Inhibitors; Gastric Emptying; Gastric Fundus; Glucagon-Like Peptide 2; In Vitro Techniques; Isoproterenol; Male; Mice; Mice, Inbred C57BL; NG-Nitroarginine Methyl Ester; Pyloric Antrum; Sodium Channel Blockers; Sympathomimetics; Tetrodotoxin; Vasoactive Intestinal Peptide

1. The neurotransmitters involved in NANC relaxation and their possible interactions were investigated in mouse isolated stomach, recording the motor responses as changes of endoluminal pressure from whole organ. 2. Field stimulation produced tetrodotoxin-sensitive, frequency-dependent, biphasic responses: rapid transient relaxation followed by a delayed inhibitory component. 3. The inhibitor of the synthesis of nitric oxide (NO), l-NAME, abolished the rapid relaxation and significantly reduced the slow relaxation. Apamin, blocker of Ca2+-dependent K+ channels, or ADPbetaS, which desensitises P2y purinoceptors, reduced the slow relaxation to 2-8 Hz, without affecting that to 16-32 Hz or the fast relaxation. alpha-Chymotrypsin or vasoactive intestinal polypeptide 6-28 (VIP6-28), antagonist of VIP receptors, failed to affect the fast component or the delayed relaxation to 2-4 Hz, but antagonised the slow component to 8-32 Hz. 4. Relaxation to sodium nitroprusside was not affected by l-NAME, apamin or ADPbetaS, but was reduced by alpha-chymotrypsin or VIP6-28. Relaxation to VIP was abolished by alpha-chymotrypsin, antagonised by VIP6-28, but was not affected by l-NAME, apamin or ADPbetaS. Relaxation to ATP was abolished by apamin, antagonised by ADPbetaS, but was not affected by l-NAME or alpha-chymotrypsin. 5. The present results suggest that NO is responsible for the rapid relaxation and partly for the slow relaxation. ATP is involved in the slow relaxation evoked by low frequencies of stimulation. VIP is responsible for the slow relaxation evoked by high frequencies of stimulation. The different neurotransmitters appear to work in parallel, although NO could serve also as a neuromodulator that facilitates release of VIP.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Adrenergic Fibers; Animals; Apamin; Cholinergic Fibers; Chymotrypsin; Dose-Response Relationship, Drug; Electric Stimulation; Enzyme Inhibitors; In Vitro Techniques; Mice; Mice, Inbred C57BL; Muscle Relaxation; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitroprusside; Receptors, Vasoactive Intestinal Peptide; Stomach; Synaptic Transmission; Thionucleotides; Vasoactive Intestinal Peptide

Prokinetic agents are frequently used in patients with bronchopulmonary dysplasia for the treatment of gastroesophageal reflux, but the effects of these agents on the airway remain unclear. This study investigated factors mediating the effects of two prokinetic agents, metoclopramide and cisapride, on contractile response to electrical field stimulation (EFS) in guinea-pig trachea segments.. Trachea segments from male Dunkin-Hartley guinea pigs were used. Concentration-response curves of metoclopramide and cisapride to electrical stimulus of 50 V at 20 Hz were obtained as baseline values. A second concentration-response curve to each prokinetic drug was obtained after preincubation with 300 microM N(G)-nitro-L-arginine-methyl ester (L-NAME, a nitric oxide synthetase inhibitor) and 2 U/mL alpha-chymotrypsin (a vasoactive intestinal peptide inhibitor). Parallel control studies were undertaken to correct for changes in the sensitivity of the tissue to EFS.. At lower concentrations (< or = 1 microM), metoclopramide reduced the contractile response to EFS, but cisapride did not have a significant effect. At concentrations greater than 1 microM, metoclopramide enhanced and cisapride suppressed the airway smooth muscle contraction evoked by EFS. However, when inhibitory nonadrenergic noncholinergic (NANC) innervations were pharmacologically abolished by L-NAME and alpha-chymotrypsin, cisapride caused augmentation and metoclopramide did not have a significant effect on the contractile response to EFS at concentrations of 1 microM or less.. This study demonstrated that the effect of metoclopramide and cisapride on the contractile response to EFS can be influenced by inhibitory NANC innervations in guinea-pig trachea.

Topics: Animals; Autonomic Nervous System; Chymotrypsin; Cisapride; Dopamine Antagonists; Electric Stimulation; Enzyme Inhibitors; Guinea Pigs; In Vitro Techniques; Male; Metoclopramide; Muscle Contraction; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Trachea; Vasoactive Intestinal Peptide

The effects of pituitary adenylate cyclase-activating peptide (PACAP-38) and vasoactive intestinal polypeptide (VIP) were investigated in the gastric fundus strips of the mouse. In carbachol (CCh) precontracted strips, in the presence of guanethidine, electrical field stimulation (EFS) elicited a fast inhibitory response that may be followed, at the highest stimulation frequencies employed, by a sustained relaxation. The fast response was abolished by the nitric oxide (NO) synthesis inhibitor L-N(G)-nitro arginine (L-NNA) or by the guanylate cyclase inhibitor (ODQ), the sustained one by alpha-chymotrypsin. alpha-Chymotrypsin also increased the amplitude of the EFS-induced fast relaxation. PACAP-38 and VIP caused tetrodotoxin-insensitive sustained relaxant responses that were both abolished by alpha-chymotrypsin. Apamin did not influence relaxant responses to EFS nor relaxation to both peptides. PACAP 6-38 abolished EFS-induced sustained relaxations, increased the amplitude of the fast ones and antagonized the smooth muscle relaxation to both PACAP-38 and VIP. VIP 10-28 and [D-p-Cl-Phe6,Leu17]-VIP did not influence the amplitude of both the fast or the sustained response to EFS nor influenced the relaxation to VIP and PACAP-38. The results indicate that in strips from mouse gastric fundus peptides, other than being responsible for EFS-induced sustained relaxation, also exerts a modulatory action on the release of the neurotransmitter responsible for the fast relaxant response, that appears to be NO.

Topics: Animals; Apamin; Carbachol; Cholinergic Agonists; Chymotrypsin; Electric Stimulation; Enzyme Inhibitors; Gastric Fundus; Guanylate Cyclase; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Muscle Contraction; Muscle Relaxation; Neuropeptides; Neurotransmitter Agents; Nitroarginine; Oxadiazoles; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Quinoxalines; Vasoactive Intestinal Peptide