Upregulation of mucosal 5-HT3 receptors is involved in restoration of colonic transit after pelvic nerve transection

Acute colonic pseudo-obstruction: A systematic review of aetiology and mechanisms

AIM

To critically review the literature addressing the definition, epidemiology, aetiology and pathophysiology of acute colonic pseudo-obstruction (ACPO).

METHODS

A systematic search was performed to identify articles investigating the aetiology and pathophysiology of ACPO. A narrative synthesis of the evidence was undertaken.

RESULTS

No consistent approach to the definition or reporting of ACPO has been developed, which has led to overlapping investigation with other conditions. A vast array of risk factors has been identified, supporting a multifactorial aetiology. The pathophysiological mechanisms remain unclear, but are likely related to altered autonomic regulation of colonic motility, in the setting of other predisposing factors.

CONCLUSION

Future research should aim to establish a clear and consistent definition of ACPO, and elucidate the pathophysiological mechanisms leading to altered colonic function. An improved understanding of the aetiology of ACPO may facilitate the development of targeted strategies for its prevention and treatment.

Low Anterior Resection Syndrome: Current Management and Future Directions

Outcomes for rectal cancer surgery have improved significantly over the past 20 years with increasing rates of survival and recurrence, specifically local recurrence. These gains have been realized during a period of time in which there has been an increasing emphasis on sphincter preservation. As we have become increasingly aggressive in avoiding resection of the anus, we have begun accepting bowel dysfunction as a normal outcome. Low anterior resection syndrome, defined as a constellation of symptoms including incontinence, frequency, urgency, or feelings of incomplete emptying, has a significant impact on quality of life and results in many patients opting for a permanent colostomy to avoid these symptoms. In this article, we will highlight the most recent clinical and basic science research on this topic and discuss areas of future investigation.

Autonomic nerve regulation of colonic peristalsis in Guinea pigs

Background/Aims

Colonic peristalsis is mainly regulated via intrinsic neurons in guinea pigs. However, autonomic regulation of colonic motility is poorly understood. We explored a guinea pig model for the study of extrinsic nerve effects on the distal colon.

Methods

Guinea pigs were sacrificed, their distal colons isolated, preserving pelvic nerves (PN) and inferior mesenteric ganglia (IMG), and placed in a tissue bath. Fecal pellet propagation was conducted during PN and IMG stimulation at 10 Hz, 0.5 ms and 5 V. Distal colon was connected to a closed circuit system, and colonic motor responses were measured during PN and IMG stimulation.

Results

PN stimulation increased pellet velocity to 24.6 ± 0.7 mm/sec (n = 20), while IMG stimulation decreased it to 2.0 ± 0.2 mm/sec (n = 12), compared to controls (13.0 ± 0.7 mm/sec, P < 0.01). In closed circuit experiments, PN stimulation increased the intraluminal pressure, which was abolished by atropine (10⁻⁶ M) and hexamethonium (10⁻⁴ M). PN stimulation reduced the incidence of non-coordinated contractions induced by NG-nitro-L-arginine methyl ester (L-NAME; 10⁻⁴ M). IMG stimulation attenuated intraluminal pressure increase, which was partially reversed by alpha-2 adrenoceptor antagonist (yohimbine; 10⁻⁶ M).

Conclusions

PN and IMG input determine speed of pellet progression and peristaltic reflex of the guinea pig distal colon. The stimulatory effects of PN involve nicotinic, muscarinic and nitrergic pathways. The inhibitory effects of IMG stimulation involve alpha-2 adrenoceptors.

Regional difference in colonic motility response to electrical field stimulation in Guinea pig

Background/Aims

In isolated guinea-pig colon, we investigated regional differences in peristalsis evoked by intrinsic electrical nerve stimulation.

Methods

Four colonic segments from mid and distal colon of Hartley guinea pigs, were mounted horizontally in an organ bath. Measurement of pellet propulsion time, intraluminal pressure, electrical field stimulation (EFS; 0.5 ms, 60 V, 10 Hz), and response of pharmacological antagonists, were performed to isolated segments of colon to determine the mechanisms underlying peristaltic reflexes evoked by focal electrical nerve stimuli.

Results

In fecal pellet propulsion study, the velocity of pellet propulsion was significantly faster in the distal colon and decreased gradually to the proximal part of the mid colon. Intraluminal pressure recording studies showed that luminal infusion initiated normal peristaltic contractions (PCs) in 82% trials of the distal colon, compared to that of mid colon. In response to EFS, the incidence of PCs was significantly increased in the distal colon in contrast, the incidence of non-peristaltic contractions (NPCs) was significantly higher in the middle-mid colon, distal-mid colon and distal colon, compared to that of proximal-mid colon. Addition of L-NAME into the bath increased the frequency of NPCs. EFS failed to cause any PCs or NPCs contractions in the presence of hexamethonium, atropine or tetrodotoxin.

Conclusions

This study has revealed that electrical nerve stimulation of distal colon is the most likely region to elicit a peristaltic wave, compared with the mid or proximal colon. Our findings suggest that EFS-evoked PCs can be modulated by endogenous nitric oxide.