Role of cGMP as a mediator of nerve-induced motor functions of the opossum esophagus

Effect of prucalopride on sildenafil-induced inhibition of esophageal peristalsis in healthy adults

BACKGROUND AND AIM

Prucalopride, a high-affinity 5-hydroxytryptamine 4 receptor agonist, promotes esophageal peristalsis, while phosphodiesterase type 5 inhibitor sildenafil inhibits esophageal peristalsis. The present study was aimed to evaluate whether prucalopride would augment esophageal peristalsis subsequent to the application of sildenafil.

METHODS

Seventeen healthy adults underwent high-resolution manometry by a catheter with one injection port located in the mid-esophagus. Secondary peristalsis was assessed by rapid air injections after water swallows. Two sessions were randomly performed including acute administration of sildenafil 50 mg after pretreatment with prucalopride or the placebo.

RESULTS

The frequency of primary peristalsis subsequent to the administration of sildenafil was significantly increased by prucalopride (P = 0.02). Prucalopride also significantly increased distal contractile integral of primary peristalsis subsequent to the administration of sildenafil (P = 0.03). No difference in the frequency of secondary peristalsis subsequent to the administration of sildenafil for air injects of 10 mL (P = 0.14) or 20 mL (P = 0.21) was found between prucalopride and placebo. Prucalopride did not change distal contractile integral of secondary peristalsis subsequent to the administration of sildenafil for air injections of 10 mL (P = 0.09) or 20 mL (P = 0.12).

CONCLUSIONS

Prucalopride modulates sildenafil-induced inhibition of primary peristalsis by increasing its effectiveness and peristaltic wave amplitude. Our findings suggest that activation of 5-hydroxytryptamine 4 receptors plays a role in mediating sildenafil-induced inhibition of esophageal primary peristalsis rather than secondary peristalsis.

Influence of sildenafil on esophageal motor function in humans: Studies using high-resolution manometry

BACKGROUND/AIM

Sildenafil induces smooth muscle relaxation of the esophagus by blocking type 5 phosphodiesterase that degrades cyclic guanine monophosphate. We aimed to characterize the effects of sildenafil on esophageal peristalsis and contraction reserve using high-resolution manometry (HRM).

METHODS

Fifteen healthy adults (12 men, age 21-39, mean 27 years) participated in this study using HRM following either sildenafil 50 mg or placebo. HRM with ten wet swallows and five multiple rapid swallows was performed in all participants. HRM metrics included esophagogastric junction contractile integral (EGJ-CI), basal lower esophageal sphincter (LES) pressure, 4-second integrated relaxation pressure (IRP-4s), distal contractile integral (DCI), distal latency, resting upper esophageal sphincter pressure (UESP), and the response to MRS.

RESULTS

Sildenafil significantly lowered EGJ-CI (P < .001), LES pressure (P = .04), IRP-4s (P = .02), and DCI (P < .001). There was no difference in UESP (P = .87) between sildenafil and placebo. Sildenafil significantly decreased peristaltic vigor, inducing absent peristalsis in 12 subjects and ineffective esophageal motility in 3 subjects. Peristaltic response and augmentation following MRS were significantly inhibited following sildenafil (7% vs 100%, P < .001, and none vs 73%, P < .001).

CONCLUSIONS

Sildenafil attenuates EGJ barrier function, resting LES pressure, and LES relaxation. Both esophageal body contractility and contraction reserve are inhibited by sildenafil in healthy adults.

Nitric oxide activation of a potassium channel (BKCa) in feline lower esophageal sphincter

AIM: To assess the effect of nitric oxide (NO) on the large conductance potassium channel (BK_Ca) in isolated circular (CM) and sling (SM) muscle cells and muscle strips from the cat lower esophageal sphincter (LES) to determine its regulation of resting tone and relaxation.

METHODS: Freshly enzymatically-digested and isolated circular smooth muscle cells were prepared from each LES region. To study outward K⁺ currents, the perforated patch clamp technique was employed. To assess LES resting tone and relaxation, muscle strips were mounted in perfused organ baths.

RESULTS: (1) Electrophysiological recordings from isolated cells: (a) CM was more depolarized than SM (-39.7 ± 0.8mV vs -48.1 ± 1.6 mV, P < 0.001), and maximal outward current was similar (27.1 ± 1.5 pA/pF vs 25.7 ± 2.0 pA/pF, P > 0.05); (b) The NO donor sodium nitroprusside (SNP) increased outward currents only in CM (25.9 ± 1.9 to 46.7 ± 4.2 pA/pF, P < 0.001) but not SM (23.2 ± 3.1 to 27.0 ± 3.4 pA/pF, P > 0.05); (c) SNP added in the presence of the BK_Ca antagonist iberiotoxin (IbTX) produced no increase in the outward current in CM (17.0 ± 2.8 vs 13.7 ± 2.2, P > 0.05); and (d) L-NNA caused a small insignificant inhibition of outward K⁺ currents in both muscles; and (2) Muscle strip studies: (a) Blockade of the nerves with tetrodotoxin (TTX), or BK_Ca with IbTX had no significant effect on resting tone of either muscle; and (b) SNP reduced tone in both muscles, and was unaffected by the presence of TTX or IbTX.

CONCLUSION: Exogenous NO activates BK_Ca only in CM of the cat. However, as opposed to other species, exogenous NO-induced relaxation is predominantly by a non-BK_Ca mechanism, and endogenous NO has minimal effect on resting tone.

Non-adrenergic non-cholinergic inhibition of gastrointestinal smooth muscle and its intracellular mechanism(s)

Relaxation of gastrointestinal smooth muscle caused by release of non-adrenergic non-cholinergic (NANC) transmitters from enteric nerves occurs in several physiologic digestive reflexes. Likely candidate NANC inhibitory agents include nitric oxide (NO), adenosine triphosphate (ATP), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), carbon monoxide (CO), protease-activated receptors (PARs), hydrogen sulfide (H2S), neurotensin (NT) and beta-nicotinamide adenine dinucleotide (beta-NAD). Multiple NANC transmitters work in concert, are pharmacologically coupled and are closely coordinated. Individual contribution varies regionally in the gastrointestinal tract and between species. NANC inhibition of gastrointestinal smooth muscle involves several intracellular mechanisms, including increase of cyclic guanosine monophosphate (cGMP), increase of cyclic adenosine monophosphate (cAMP) and hyperpolarization of the cell membrane via direct or indirect activation of potassium ion (K+) channels.

Regulation of basal tone, relaxation and contraction of the lower oesophageal sphincter. Relevance to drug discovery for oesophageal disorders

The lower oesophageal sphincter (LOS) is a specialized region of the oesophageal circular smooth muscle that allows the passage of a swallowed bolus to the stomach and prevents the reflux of gastric contents into the oesophagus. The anatomical arrangement of the LOS includes semicircular clasp fibres adjacent to the lesser gastric curvature and sling fibres following the greater gastric curvature. Such anatomical arrangement together with an asymmetric intrinsic innervation and distinct proportion of neurotransmitters in both regions produces an asymmetric pressure profile. The LOS tone is myogenic in origin and depends on smooth muscle properties that lead to opening of L-type Ca(2+) channels; however it can be modulated by enteric motor neurons, the parasympathetic and sympathetic extrinsic nervous system and several neurohumoral substances. Nitric oxide synthesized by neuronal NOS is the main inhibitory neurotransmitter involved in LOS relaxation. Different putative neurotransmitters have been proposed to play a role together with NO. So far, only ATP or related purines have shown to be co-transmitters with NO. Acetylcholine and tachykinins are involved in the LOS contraction acting through acetylcholine M(3) and tachykinin NK(2) receptors. Nitric oxide can also be involved in the regulation of LOS contraction. The understanding of the mechanisms that originate and modulate LOS tone, relaxation and contraction and the characterization of neurotransmitters and receptors involved in LOS function are important to develop new pharmacological tools to treat primary oesophageal motor disorders and gastro-oesophageal reflux disease.

The effect of sildenafil on segmental oesophageal motility and gastro-oesophageal reflux

BACKGROUND

Sildenafil is an inhibitor of type 5 phosphodiesterase. It relaxes or inhibits contraction of smooth muscle by increasing cellular concentrations of cyclic guanosine monophosphate. Multichannel intraluminal impedance manometry/pH allow the precise evaluation of oesophageal bolus transit and acid/non-acid reflux.

AIM

To investigate the effect of sildenafil on segmental oesophageal motor function and gastro-oesophageal reflux.

METHODS

Eight healthy volunteers underwent multichannel intraluminal impedance manometry baseline, and 15, 30 and 45 min before and after a 50-mg dose of sildenafil successively. The subjects underwent 2-h multichannel intraluminal impedance/pH studies on two separate days after either water or sildenafil ingestion.

RESULTS

Sildenafil decreased the resting lower oesophageal sphincter pressure and prolonged the duration of lower oesophageal sphincter relaxation for the 45 min following its ingestion. At 15 min, distal onset velocity, total bolus transit time, bolus presence time and segmental transit time were delayed in the mid to distal oesophagus. At 30 min, distal onset velocity was restored but bolus presence time and bolus presence time were still delayed in distal smooth muscle segment. At 45 min, total bolus transit time and distal onset velocity were restored but bolus presence time and segmental transit time were delayed more in the transition zone. Sildenafil did not alter the reflux.

CONCLUSION

Sildenafil alters lower oesophageal sphincter function and oesophageal bolus transit, but not induce gastro-oesophageal reflux.

Esophageal dysmotility and the change of synthesis of nitric oxide in a feline esophagitis model

The present study explores the changes of nitric oxide synthesis and esophageal dysmotility in a feline model of esophagitis. Perfusion of the esophagus with acid produced inflammatory changes of esophageal mucosa. The esophageal motility was measured before and after the perfusion. The nitric oxide synthase activity, the l-arginine uptake, and the content of cyclic guanine monophosphate of the muscle and the mucous membrane were determined and the NADPH-diaphorase was stained. Esophagitis impairs the motility of the esophagus. The nitric oxide synthase activity, the content of cyclic guanine monophosphate, the NADPH-diaphorase stain and the maximum velocity of l-arginine uptake of lower esophageal sphincter of the cats in the acid perfusion group were higher than those of the control group. The maximum velocity of l-arginine transport and the content of cyclic guanine monophosphate of the mucosa in the acid perfusion group were lower than those of the control group. The results suggested that during esophagitis there is an alteration of the l-arginine/nitric oxide synthase/nitric oxide pathway in the esophagus, which may be one of the important mechanisms of esophageal motility dysfunction.