Effects of morphine on electrical activity of the rectum in man

Nitric oxide production is diminished in colonic circular muscle from acquired megacolon

PURPOSE

Nitric oxide modulates human colonic smooth muscle function. To determine whether nitric oxide production is altered in colon from acquired megacolon, we measured cholinergic nerve-mediated contractions in vitro before and after inhibition of nitric oxide synthase.

METHODS

Intramural nerves in circular smooth muscle from histologically normal colon (n = 12) and acquired megacolon (n = 3) were activated by electrical field stimulation.

RESULTS

In controls blockade of nitric oxide synthase by N(G)-Nitro-L-Arginine induced increases (P < 0.05) in amplitude of contractions; these increases in amplitudes were blocked by L-Arginine (analysis of variance; P < 0.05). By contrast, blockade of nitric oxide synthase did not increase amplitudes of contractions with circular smooth muscle from acquired megacolon. An immediate phasic contraction was blocked by atropine sulfate.

CONCLUSIONS

The results support the concept that nitric oxide production modulates cholinergic nerve-mediated contractions in normal colonic circular muscle, whereas acquired megacolon is associated with altered release of this inhibitory neurochemical. Potential explanations include depletion of tissue L-Arginine, decreased capacity to recycle citrulline to arginine, or decreased release of vasoactive intestinal peptide from circular smooth muscle in acquired megacolon.

Is colonic electrical activity a similar phenomena to small-bowel electrical activity?

PURPOSE

This study was designed to investigate colonic spike bursts regarding 1) their migration behavior, 2) their pressure correlates, and 3) comparing colonic short spike bursts with spike bursts from migrating myoelectric complex from the small bowel.

METHODS

Rectosigmoid electromyography and manometry were recorded simultaneously in seven normal volunteers and electromyography alone in five others during two hours of fasting and for two hours after one 2,100-kJ meal. One patient with an ileostomy was also studied by the same method to record the migrating myoelectric complex from the terminal ileum during fasting.

RESULTS

Three kinds of spike bursts were observed in the pelvic colon: rhythmic short spike bursts, migrating long spike bursts, and nonmigrating long spike bursts. The meal significantly increased the number of migrating and nonmigrating long spike bursts (from 25 to 38.7 percent of the recording time; P < 0.01). These bursts of potentials showed a peak 15 minutes after the meal, which may be caused by the gastrocolic reflex. Migrating long spike bursts started anywhere along the rectosigmoid and migrated from there aborad 82 percent of the time and orad or in both directions in 10 or 7 percent of the time, respectively. They originated pressure waves 99 percent of the time. Short spike bursts were more frequent before the meal (15.1 percent before and 9.6 percent after the meal), but the difference was not significant; they neither propagated nor initiated pressure waves detected by the mini-balloon.

CONCLUSIONS

Migrating long spike bursts were the only potentials that migrated, sometimes for short distances. Short spike bursts are a different phenomenon from the small-bowel migrating myoelectric complex because they do not migrate; they can occur during the postprandial period and never originated intraluminal pressure waves.

Decreased vasoactive intestinal peptide levels and glutathione depletion in acquired megacolon

We reported decreased vasoactive intestinal peptide levels in acquired megacolon. The origin of altered neuropeptide levels is unknown, but recent work suggested that tissue antioxidants may function as neuroprotectants. Our hypothesis was that altered levels of inhibitory neurotransmitters in human colon are associated with depletion of the tripeptide thiol, glutathione. Normal colon samples (N = 10; from patients 41-80 years old) and acquired megacolon samples (N = 10; from patients 31-98 years old) were obtained at surgery. Vasoactive intestinal peptide levels were decreased in muscularis externa from acquired megacolon (P = 0.01), while there was a modest increase in NADPH diaphorase activity in muscularis externa from megacolon (P = 0.10). Glutathione in acquired megacolon was detectable in muscularis externa from only five specimens (P < 0.05), but was not significantly different (P > 0.05) in the mucosal-submucosal layer. The results supported the presence of vasoactive intestinal peptide and NADPH diaphorase in distinct subpopulations of nerves in human colon. The results also supported the hypothesis that glutathione functions as a neuroprotectant in a subset of patients with acquired megacolon.

[Physiology of fecal continence and defecation]

Defaecation is a complex function that requires interactions between the somatic and autonomic nervous systems. Moreover, social living standards lead to self-control of continence involving supraspinal nervous structures. After a brief description of the anatomy of the hind gut, the various reflex mechanisms underlying faecal continence and defaecation are exposed; the specificities of the nervous control of the smooth and striated muscles brought into play in these events are detailed. Then the main useful investigations allowing to localize the nervous structures at the origin of the anorectal disorders are reviewed.

Concordance between colonic myoelectrical signals recorded with intramuscular electrodes in the human rectosigmoid in vivo

The myoelectrical activity of the human rectosigmoid colon was studied simultaneously in six subjects at two sites using two pairs of fine wire bipolar electrodes. The electrodes were spaced 2-5 cm apart in the rectosigmoid after insertion into the smooth muscle layers under direct vision at sigmoidoscopy. The electrodes were implanted at positions between 8 and 25 cm from the anal verge in different subjects. The frequency of myoelectrical burst activity together with the burst duration recorded by each electrode pair was examined. The relation of burst frequency and burst duration in the higher and lower placed electrodes was also assessed. In none of the subjects was three evidence of synchrony between the electrode pairs. In addition, there was no relation between the relative position of the electrodes and the intrinsic frequency of duration of myoelectrical bursts. It is concluded that regions of smooth muscle in the unstimulated human colon in vivo act independently and that there is no effective common neuromuscular drive under these conditions.

Effects of stimulation of vesical afferents on colonic motility in cats

The effects of distension and isovolumetric contraction of urinary bladder on colonic motility were studied in anesthetized cats. Distension and contraction of the urinary bladder induced an inhibition of spontaneous colonic electromyographic activity and a decrease in the amplitudes of the excitatory junction potentials evoked in the colon by stimulation of the distal end of the parasympathetic nerve fibers. This inhibition was blocked by guanethidine and phentolamine. Reversely, vesical emptying resulted in an increase in colonic motility, abolished by atropine, and an increase in the amplitude of the excitatory junction potentials. Both excitatory and inhibitory reflexes disappeared after hexamethonium. The inhibitory effects of bladder distension were abolished by bilateral section of the lumbar ventral or dorsal spinal roots and after bilateral section of the lumbar colonic or hypogastric nerves. These results indicate (a) that the vesical afferents responsible for the inhibitory and excitatory reflexes run in the hypogastric and pelvic nerves respectively and (b) that the inhibitory and excitatory effects are caused by the activation of sympathetic and parasympathetic efferent nerve fibers, respectively. The supraspinal nervous structures were not implicated in these reflexes because they persisted in spinal cats.

Human rectosigmoid electromyography: a new approach and some pitfalls

A method has been developed to record directly myoelectrical activity from the smooth muscle of the colon of intact subjects using pairs of intramuscular wires. Discrete bursts of myoelectrical activity occurred at 4-20 per min. A small interelectrode distance in this method allows contamination of colonic myoelectrical activity by the electromyogram of skeletal muscle to be excluded. This artefact has not been considered in previous recordings of 'colonic' activity.