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The role of enterohepatic circulation and specific bile acids in the initiation and caudad migration of duodenal migrating motor complexes (MMCs) was investigated in conscious dogs. All dogs had spontaneous duodenal MMCs that migrated to the terminal ileum when bile flow was intact. During the first 3 days after total external biliary diversion, no MMCs originated in the duodenum. Instead, all MMCs originated in the jejunum and migrated to the ileum. During the next 4 days of total external biliary diversion, 81% of the MMCs originated in the jejunum and 19% in the duodenum. When normal bile flow was restored after 9 days of total external biliary diversion, regular duodenal MMCs resumed after a delay of 126 +/- 27 minutes. Perfusion of individual bile acids or dogs' own bile, but not saline or alkaline solution, into the duodenum or perfusion of dogs' own bile directly into the ileum during total external biliary diversion restarted duodenal MMCs with a time lag of about 2 hours. The authors conclude that intact enterohepatic circulation is essential for the initiation of regular duodenal MMCs.

The effects of an antibacterially effective IV dose of erythromycin on gastrointestinal motor activity were investigated in eight normal healthy human volunteers in the fasted state and the fed state. Motor activity was recorded by a multilumen manometric tube. Data were analyzed visually and by a computer method. Blood samples were obtained for erythromycin and motilin assays. In the gastric antrum, erythromycin significantly increased the total duration, amplitude, and area under contractions from 0 to 60 minutes and frequency of contractions from 0 to 30 minutes from the start of its infusion in the fasted state. A similar response in the fed state occurred mostly from 0 to 30 minutes after the start of erythromycin infusion. By contrast, erythromycin inhibited the frequency and decreased the duration of small intestinal contractions in the fed state but had no effect in the fasted state. The gastric motor response was related to the plasma concentration of erythromycin, but not to plasma motilin. Erythromycin significantly shortened the duration of migrating motor complex disruption by a meal. Erythromycin also induced symptoms of upper abdominal pain, bloating, and nausea. Abdominal pain was related to strong antral contractions in both fasted and fed states; bloating occurred only in the fed state. Nausea occurred in both fasted and fed states, but it was not related to any specific pattern of motor activity. It is concluded that the strong antral contractions induced by erythromycin may accelerate the rate of gastric emptying, but they may also be responsible for causing the sensations of upper abdominal pain and bloating. The motor response to erythromycin is less during the fed than during the fasted state. The strong antral contractions induced by erythromycin are not mediated by the release of motilin.

Determination of plasma levels of vasoactive intestinal polypeptide (VIP) has been used for screening patients with chronic diarrhea to identify potential neuroendocrine tumors. This 6-year blinded study from 1981 to 1986 examines the causes of elevated VIP levels in patients. In healthy volunteers ( n = 144), VIP concentrations ranged from 14 to 76 pg/mL (mean +/- SE, 28 +/- 12), whereas in chronic renal failure, 4 of 34 patients or 12% [serum creatinine 4.5 - 9.0 mg/dL (397-795 mumols/L)] had an elevation to greater than 100 pg/mL. No patient with idiopathic hepatic cirrhosis (n = 12) had elevation of serum concentration of this peptide. Among 588 consecutive unselected patients undergoing evaluation for chronic diarrhea (n = 362; 62%) or possible neuroendocrine tumor (n = 214; 36%), 23 patients (3.9%) had concentrations greater than 76 pg/mL. In this group, 5 patients had functioning (VIP, 160-5975 pg/mL) and 5 had nonfunctioning (VIP, 80-120 pg/mL) pancreatic islet cell carcinomas: all 10 patients had hepatic metastases. Other known cases of elevated levels of VIP, ranging from 80 to 340 pg/mL, included other neurogenic tumors (n = 3), small- bowel resection (n = 2), inflammatory bowel disease (n = 2), chronic renal failure (n = 1), and prolonged fasting (n = 1). Patients with diarrhea in which VIP-secreting tumors were identified had plasma vasoactive intestinal peptide concentrations greater than 140 pg/mL. In patients with chronic diarrhea, determination of plasma vasoactive intestinal peptide levels did identify tumors secreting this peptide, but the results from this referral institution did not show identification of these tumors early in their clinical course.

To determine whether decreased tissue vasoactive intestinal polypeptide levels might affect inhibitory neural input, fresh colonic specimens were obtained from patients with Crohn's colitis (n = 7) and normal subjects (n = 13). Immunoreactive vasoactive intestinal polypeptide levels were measured in the muscularis externa by radioimmunoassay and localized in tissue sections by immunostaining. Circular muscle strips were maintained in an organ bath; inhibitory junction potentials evoked by short- and long-duration field stimulation and resting membrane potentials were recorded using intracellular impalements. In Crohn's colitis, vasoactive intestinal polypeptide levels displayed a bimodal distribution in which 3 specimens had vasoactive intestinal polypeptide levels greater than or equal to 4 SE lower than the mean in normal specimens. In 3 specimens from Crohn's colitis with decreased vasoactive intestinal polypeptide levels, immunoreactive material was absent from the circular muscle layer and the myenteric plexus. Mean resting membrane potentials, mean amplitude of inhibitory junction potentials evoked by short-duration stimulation, and mean amplitude of initial inhibitory junction potentials evoked by long-duration stimulation were not different between the two groups. However, the mean amplitude of the 60th inhibitory junction potential during prolonged stimulation was decreased (p less than 0.01) in Crohn's colitis (6 mV) compared with normal specimens (11 mV). These results show that diminished neural input to circular muscle in Crohn's colitis was associated with decreased extractable vasoactive intestinal polypeptide levels and decreased staining of nerve fibers containing vasoactive intestinal polypeptide.

Previous studies in the ferret demonstrated that vagal nerve stimulation induced an atropine-resistant water secretion. Substance P and vasoactive intestinal polypeptide are possible mediators of this secretory response. The objectives of this study were to investigate the in vivo effects of substance P and vasoactive intestinal polypeptide on the jejunal musculature and epithelium. Substance P caused an increase in jejunal motility, water secretion, and transmural potential difference. Cholinergic blockade did not affect the substance P-induced contractions, but did reduce the increase in transmural potential difference, suggesting an inhibition of water secretion. Vasoactive intestinal polypeptide abolished motor activity; however, it induced an increase in transmural potential difference that was atropine and tetrodotoxin resistant. By immunohistochemical methods, immunoreactive vasoactive intestinal polypeptide and immunoreactive substance P were localized to both nerve cell bodies and nerve fibers in the ferret intestine. Determination of intestinal concentrations of vasoactive intestinal polypeptide and substance P in the ferret showed concentrations of these two neuropeptides that were similar to those in human intestine and demonstrated much higher concentrations of these substances in the muscular layer than in the epithelial layer. Our data demonstrate that in the ferret substance P excites and vasoactive intestinal polypeptide inhibits jejunal motor activity. However, both peptides increase water secretion. Our results suggest that in response to vagal stimulation, neuronally released substance P or vasoactive intestinal polypeptide may participate in the atropine-resistant water secretion.

Spontaneous contractions, inhibitory responses produced by electrical field stimulation, and some electrophysiologic properties of circular smooth muscle from normal sigmoid colon and from sigmoid colon of ulcerative colitis patients were compared in vitro using simultaneous recordings of mechanical and intracellular electrical activity. In normal colonic circular muscle obtained from 21 patients, the frequency of spontaneous summation contractions ranged from 3 to 7 per 4 min, whereas in circular muscle from 13 patients with ulcerative colitis, the frequency of these contractions ranged from 1 to 9 per 4 min. Nonadrenergic, noncholinergic relaxation produced by electrical field stimulation was recorded in the majority of circular smooth muscle strips from both normal colon and colon from patients with ulcerative colitis. There were no significant differences in mean resting membrane potential, mean slow-wave frequency, mean maximum slow-wave amplitude, or inhibitory-junction potential amplitudes recorded using circular smooth muscle from both normal colon and colon from patients with ulcerative colitis. There appeared to be a weak association in patients with ulcerative colitis between increasing duration of symptoms and decreasing frequency of spontaneous summation contractions, but there were no associations between the frequency of these contractions and the severity of colonic inflammation, patient age, or the frequency of stools. The mechanism accounting for a wider range in the frequency of summation contractions recorded from colonic circular smooth muscle in ulcerative colitis remains to be determined.

To investigate the reported association between idiopathic chronic constipation and morphologic abnormalities of enteric nerves, we measured the concentrations of six neuropeptides, vasoactive intestinal peptide, peptide histidine-methionine, substance P, methionine5-enkephalin, neuropeptide Y, and the bombesinlike intestinal peptides, in descending colon from 4 patients with idiopathic chronic constipation. Decreased concentrations of vasoactive intestinal peptide (707 +/- 112 ng/g wet tissue) and peptide histidine-methionine (543 +/- 58 ng/g) were found in the muscularis externa obtained from constipated patients compared with normal concentrations (40 patients) of vasoactive intestinal peptide (1199 +/- 47 ng/g) and peptide histidine-methionine (815 +/- 45 ng/g). Vasoactive intestinal peptide was identified by immunocytochemistry in nerve fibers within the circular smooth muscle layer of descending colon obtained from 6 control patients, but not in nerve fibers within the circular smooth muscle of descending colon obtained from 3 patients with idiopathic chronic constipation. By contrast, the distribution of immunoreactive met5-enkephalin was similar in normal descending colon and in descending colon obtained from patients with idiopathic chronic constipation. Decreased colonic concentrations of vasoactive intestinal peptide (a candidate nonadrenergic, noncholinergic inhibitory neurotransmitter) may be associated with diminution of inhibitory innervation of colonic circular smooth muscle in some patients with idiopathic chronic constipation.