Plasma somatostatin-like immunoreactivity during the interdigestive period in the dog.

To study possible physiologic relationships between somatostatin and the gastric interdigestive contractions (GIC), gastric motor activity, and plasma somatostatin-like immunoreactivity (SLI) concentration were determined simultaneously in four conscious dogs, each of which was studied on two separate occasions. Plasma SLI level was highest during the GIC period and lowest 60 and 80 min after the cessation of the GIC; the mean difference in plasma SLI was 41 +/- 6 pg/ml. When synthetic motilin, a known stimulus of GIC, was infused at a physiologic rate during the period in which plasma SLI levels were low, SLI rose to approximately the same values observed during the contraction period and GIC similar to those that occur spontaneously were observed. When synthetic somatostatin, a known inhibitor of endogenous motilin release, was infused at a rate that raised the plasma SLI to approximately the levels observed during the contraction period (0.1 microgram/kg per h), the appearance of the subsequent GIC was significantly delayed. These results are consistent with a physiological role for somatostatin in the regulation of GIC in dogs and suggest an interrelationship between motilin and somatostatin.

Relationship of sphincter of Oddi spike bursts to gastrointestinal myoelectric activity in conscious opossums.

The oppossum sphincter of Oddi (SO) exhibits peristaltic spike bursts with accompanying contraction waves that originate proximally in the sphincter of Oddi and propagate toward the duodenum. In this study we recorded myoelectrical activity of the opossum SO and upper gastrointestinal tract in six conscious animals using chronically implanted electrodes. Biopolar electrodes were implanted in the gastric antrum, duodenum, SO segment, jejunum, and ileum. During fasting the frequency of SO spike bursts, scored as number per minute, showed a cyclic pattern consisting of four phases (A to D). Phase A had a low spike burst frequency of approximately 2/min that lasted approximately 20 min. In phase B, the spike burst frequency increased progressively during a 40-45 min interval culminating in a short interval of phase C activity characterized by a maximal spike burst frequency of approximately 5/min. During phase D, the spike bursts decreased over 15 min to merge with the low frequency of phase A and the cycle repeated. Cycle length of the interdigestive SO cycle, 87+/-11 SD min, was virtually identical with that of the interdigestive migrating myoelectric complex (MMC) of the upper gastrointestinal tract. The onset of phase C activity in the SO began 1-2 min before phase III of the MMC activity in the duodenum. Feeding abolished the cyclic pattern of spike burst activity in the SO as well as in the upper gastrointestinal tract. After feeding the SO spike bursts occurred at a frequency of 5-6/min for at least 3 h. We conclude that: (a) During fasting, the oppossum SO exhibits cyclic changes in its spike burst frequency; (b) Maximal spike burst frequency of the SO occurs virtually concurrent with passage of phase III MMC activity through the duodenum and; (c) Feeding abolishes the interdigestive cyclic spike burst pattern of the SO as well as that of the gastrointestinal tract.

Mitemcinal (GM-611), an orally active motilin agonist, facilitates defecation in rabbits and dogs without causing loose stools.

The effects of mitemcinal (GM-611), an orally active motilin agonist, on defecation were investigated in rabbits and dogs. In normal rabbits, within 0-3 h of dosing, orally administered mitemcinal (2.5-10 mg kg(-1)) increased stool weight in a dose-dependent manner without causing loose stools. Sennoside (12-48 mg kg(-1)) also facilitated defecation within 2-9 h of oral administration, but the stools were significantly loosened. In the morphine-induced constipation model, the stool weight of morphine-treated rabbits (1 mg kg(-1)) was only 37.5% of that of untreated animals. Mitemcinal (0.5-20 mg kg(-1)) dose-dependently increased stool weight without increasing stool water content. At the highest dose of mitemcinal, stool weight recovered to 83.9% of that of untreated animals. In normal dogs, mitemcinal (0.3-3 mg kg(-1)) reduced the time to first bowel movement after oral administration without inducing diarrhoea at any dose. These results indicate that mitemcinal facilitates defecation without inducing severe diarrhoea. It is suggested that mitemcinal may be a novel therapeutic agent for constipation that enables easier control of the timing of defecation because of the early onset and short duration of its action, compared with sennoside.

Gastroduodenal motility in neonates: response to human milk compared with cow's milk formula.

It is known that breast milk empties more quickly from the stomach than does infant formula. We studied the difference in gastroduodenal motility between neonates fed with human milk and those fed with infant formula. Twenty-four five- to 36-day-old neonates were fed with mother's breast milk or with a cow's milk-based formula. Postprandial gastroduodenal contractions were recorded manometrically for three hours. Repetitive, high-amplitude nonmigrating contractions were the dominant wave form during the postprandial period. The number of episodes, duration, amplitude, and frequency of nonmigrating contractions were not different following the different feedings. The migrating myoelectric complex, which signals a return to the interdigestive (fasting) state, appeared in 75% of breast milk-fed infants but only 17% of formula-fed infants (P less than .05) within the three-hour recording period. Because contractions were similar following the two meals, but a fasting state recurred more rapidly in breast-fed infants, we conclude that factors other than phasic, nonpropagated antroduodenal contractions were responsible for the differences in gastric emptying between breast milk and formula.

The negative feedback mechanism of gastric acid secretion: Significance of acid in the gastric juice in man and dog.

As reported previously, gastrin-stimulated gastric secretion in the dog and in man was suppressed by an intravenous infusion of secretin, These results, both in the dog and in man, also were obtained by introduction of acid into the duodenum, which indicated that both endogenous and exogenous secretion inhibit gastrin-stimulated gastric secretion at the oxyntic cell level. Feeding a test meal in man gave rise to an increase of plasma gastrin, reaching a peak of 120 pg. per milliliter at 15 minutes after feeding and remaining above control level for 2 to 3 hours. Is was found that plasma gastrin was suppressed greatly during the intravenous infusion of pure secretin. In animal experiments endogenous gastrin release produced by irrigation of the antral pouch also inhibited both endogenous and exogenous secretin. These results indicate that secretin inhibits gastrin release at the G-cell level in the antrum. On the other hand, it also was observed that endogenous gastrin release ceased when the pH of the perfusate dropped below 2.5. The following conclusions are drawn from the above findings. (1) Gastrin release is suppressed primarily by direct contact of acid with the antrum. The feedback mechanism in this case operates intraluminally in the stomach. (2) The low pH content of the stomach stimulates the release of secretin from the duodenum. The secretin released in this way not only inhibits gastric acid secretion at the oxyntic cell secretin released in this way not only inhibits gastric acid secretion at the oxyntic cell secretin released of gastrin at the G-cell level in the antrum. The level but also blocks the release of gastrin at the G-cell level in the antrum. The feedback mechanism brought about by acid of gastric origin occurs through the general circulation.

Motilin and clinical application.

Motilin is a regulatory polypeptide of 22 amino acid residues and orginates in motilin cells scattered in the duodenal epithelium of most mammals and chickens. Motilin is released into the general circulation at about 100-min intervals during the interdigestive state and is the most important factor in controlling the interdigestive migrating contractions. Recent studies have revealed that motilin stimulates endogenous release of the endocrine pancreas. Clinical application of motilin as a prokinetic has become possible since erythromycin and its derivatives were proved to be nonpeptide motilin agonists.

Neurohormonal control of gastrointestinal motor activity in conscious dogs.

Interdigestive migrating contractions (IMC) were analyzed for their occurrence interval, duration, migrating velocity, and frequently in long term records obtained by means of chronically implanted force transducers in the main stomach and the extrinsically denervated fundic pouches or in the intact jejunum and the extrinsically denervated Thirty loop in 10 conscious dogs. Plasma immunoreactive motilin (IRM) was measured simultaneously. It was found that concomitant occurrence of IMC in the main stomach and pouch was closely associated with increase in plasma IRM concentration. On the other hand, in the extrinsically denervated jejunal loop, IMC-like contractions occurred independently of and more frequently than those in the intact jejunum and did not correlate with an increase in IRM concentration. It is concluded that gastric motor activity is under humoral control but in the jejunum, autoregulation by the intrinsic nerve plexus is more predominant than humoral factor(s).

Motilin and gallbladder: new dimensions in gastrointestinal physiology.

Intravenous infusion of motilin (0.3-0.9 micrograms/kg-hr) during the interdigestive state induced a transient but strong tonic contraction in the gallbladder, which was similar to the natural interdigestive gallbladder contraction, as well as a typical IMC in the stomach and the duodenum. This motilin-induced contraction always occurred simultaneously with the intitiation of phase II contractions of the IMC in the duodenum. The increase in contractile force (11.5 +/- 0.57 g) was not related to the dose of motilin tested. In contrast, intravenous infusion of CCK-octapeptide (CCK-OP, 0.03-0.09 micrograms/kg-hr) induced a dose related tonic contraction (7.8 +/- 0.41-17-7 +/- 0.77 g) which lasted as long as the CCK-OP infusion continued during the interdigestive state. Atropine sulfate (0.025 mg/kg) strongly inhibited both motilin- and CCK-OP induced gallbladder contractions. The present study indicates that the canine gallbladder in the conscious state is responsive to at least two hormonal factors, motilin and CCK. The contractile response of the gallbladder to motilin is quite different from the response to CCK-OP. However, both responses are mediated at least partially by cholinergic pathways.

Muscarinic control of phase III contractions and motilin release in dogs.

The role of muscarinic receptor subtype(s) in the control of gastric phase III contractions and motilin release was determined in dogs. Pirenzepine (226 nmol/kg/h) shortened the phase III cycle, causing an early increase in plasma motilin concentrations. Both AF-DX116BS and 4-DAMP inhibited the occurrence of spontaneous and motilin-induced phase III contractions, and 4-DAMP also inhibited the spontaneous increase in plasma motilin concentration. Only 4-DAMP inhibited carbachol-induced motilin release in perifused duodenal mucosal cells. In conclusion, M1 receptors are involved in the indirect inhibition of motilin release. Motilin-induced contractions are mediated mainly by M3 receptors and partly by M2 receptors, and M3 receptors are present in motilin-producing cells.

Relationship between gallbladder bile concentration and motility in conscious dogs: role of cholecystokinin.

The relationship between gallbladder (GB) bile concentration and motility was studied in conscious dogs. The 12-h GB bile concentrations between meals could be divided into three periods: diluting, minimum, and concentrating periods. During the diluting period, inhibition of GB contractions by a CCKA receptor antagonist, atropine or hexamethonium, resulted in concentration of GB bile, whereas during the concentrating period, CCK-8 shifted the concentration process back to dilution. The GB appears to absorb water continuously from GB bile, which is not regulated by cholinergic or CCKA receptors. The postprandial progressive dilution of GB bile is brought about by GB pumping controlled by cholecystokinin (CCK).

Does motilin control interdigestive pepsin secretion in the dog?

Pepsin output in the Heidenhain pouch, plasma motilin concentration, and contractile activity in the pouch and the main stomach were investigated in five dogs. During the interdigestive state, the pepsin output was significantly increased with a cyclic increase in contractile activity in both the pouch and main stomach at approximately 100-min intervals. The plasma immunoreactive motilin (IRM) concentration fluctuated during the interdigestive state, and, peaks of IRM concentration coincided with the maximum pepsin secretory activity. Exogenous administration of motilin (0.5 micrograms/kg-hr) increased contractile activity in the main stomach and pouch quite similar to the natural interdigestive migrating contractions (IMC), and increased pepsin output significantly. Atropine pre-treatment suppressed the naturally-occurring and motilin-induced pepsin output and contractions in the pouch. It is concluded that pepsin output and contractions in the Heidenhain pouch increase in close association with the IMC in the main stomach during the interdigestive state and these cyclic motor and secretory events in the vagally denervated fundic pouch are most likely regulated by motilin through the intramural cholinergic pathway.

Immunocytochemical localization of motilin-containing cells in the rabbit gastrointestinal tract.

Motilin-immunopositive cells (Mo cells) are known to be present in the upper small intestine of various species, including man. However, whether Mo cells are present in the rabbit gastrointestinal tract remained to be elucidated. Therefore, this study was designed to investigate the distribution of Mo cells in the rabbit gastrointestinal tract by the avidin-biotin-peroxidase complex method using a new anti-motilin serum (CPV2) raised in chickens. The results of an enzyme-linked immunosorbent assay suggested that this antiserum recognized the C-terminal region of the motilin molecule. Motilin-immunopositive cells were found in the epithelia of the crypts and villi throughout the rabbit gastrointestinal tract from the gastric antrum to the distal colon, but no immunostaining occurred in the gastric body. Morphometric analysis revealed that Mo cells were localized preferentially in the upper small intestine, as reported for other species, and the cell densities (cells/mm2, mean +/- SE) were: gastric antrum (0.41 +/- 0.16), duodenum (8.2 +/- 0.8), jejunum (1.9 +/- 0.5), ileum (0.62 +/- 0.14), cecum (0.19 +/- 0.05), proximal colon (0.13 +/- 0.03), and distal colon (0.39 +/- 0.18). Our results demonstrated conclusively that Mo cells exist in the rabbit gastrointestinal tract and showed for the first time their regional distribution. Furthermore, our new chicken antiserum would appear to be a useful tool for the determination of plasma motilin concentrations by radioimmunoassay and for the immunoneutralization of endogenous motilin in the rabbit.

Localization of motilin-immunopositive cells in the rat intestine by light microscopic immunocytochemistry.

Motilin-immunopositive cells (Mo cells) are known to exist in the upper small intestine of many species including man. However, the possible presence of Mo cells in the rat gastrointestine has remained obscure because antiserum against it raised in rabbit was found not to cross-react with motilin in the rat gastrointestine. The present study was designed to investigate the distribution of Mo cells in the rat gastrointestine by the peroxidase-conjugated second antibody method using newly raised chicken anti-motilin serum (CPV3). This antiserum was suggested to recognize the N-terminal region of the motilin molecule by enzyme-linked immunosorbent assays and immunocytochemical absorption test. Mo cells detected in the rat gastrointestine by immunocytochemistry were found to be distributed in the duodenum (1.5 cells/mm2), jejunum (2.2 cells/mm2), and ileum (0.028 cells/mm2), and no positive cells were found in the gastric body, gastric antrum, cecum, colon, or pancreas. The immunopositive cells in the rat intestine were spindle shaped or polygonal, scattered throughout the epithelium of the villi and crypts, and similar to those commonly observed in the upper small intestine of other species. These results indicate for the first time that motilin-immunopositive cells do exist in the rat intestine.

Biotinyl C-terminal-extended motilin as a biologically active receptor probe.

The synthesis, purification, and characterization of biotinylated analogues of motilin are reported. The C-terminal of canine motilin was extended by the addition of a cysteine residue, and then biotinylated. Biotinyl motilin was purified by following HPLC and characterized by amino acid analysis. Biotinylation of the ligand was confirmed by ELISA assay with the avidin-biotin system. Biotinyl motilin showed similar affinity for binding to rabbit gastric membrane fraction compared to unlabeled canine motilin, and also retained functional activity in its ability to cause contraction of rabbit duodenal segments. To determine the binding of biotinyl motilin in isolated rabbit antral smooth muscle, cells were incubated with the biotinyl motilin with and without excess of unlabeled motilin. Subsequent addition of avidin-biotinylated peroxidase complex showed the distribution of reaction products over the cell surface. Bioactive biotinyl motilin provides a useful probe for the demonstration of cell surface motilin receptors and will facilitate receptor purification and characterization.

Distribution of enteric neural peptide YY in the dog gastrointestinal tract.

Various regions of the dog gastrointestinal tract were investigated for the distribution of peptide YY (PYY) neurons using immunocytochemistry and radioimmunoassay. PYY neurons that encircled non-PYY-immunoreactive neurons were mainly observed in the myenteric plexus from the stomach to the colon. There was more PYY-like immunoreactivity in the muscle layer of the stomach and ileum than in the other intestines. The results of high performance liquid chromatography revealed that neural PYY-immunoreactive substance is identical to authentic PYY. PYY was not localized in the cholinergic neurons. These results indicate that PYY, as a neuropeptide, is involved in the regulation of gastrointestinal function.

Growth hormone releasing factors in the brain and the gut: chemistry, actions, and localization.

Within the physiological range of other known releasing factors, human pancreatic tumor growth hormone releasing factor (hpGRF) is specific for GH release. Data concerning hpGRF action on cAMP and GH are consistent with the concept of cAMP acting as a second messenger for this releasing factor. hpGRF-stimulated GH release is Ca++ dependent. Exogenous hpGRF40 does not alter the interdigestive gastric motility or secretion of gastrin and motilin in dogs, while large doses of hpGRF stimulate somatostatin release into the hepatic portal blood of the rat. Significant GRF activity as determined by a rat pituitary perifusion system is confined within the median eminence and the arcuate nucleus, though detectable but insignificant GRF activity is present in other area of the hypothalamus and cortex in the rat. GRF activity is present in the ovine brain as well as in the gut. Both tissues contain large (between 4000-5000 daltons) and small (but possibly larger than 1000 daltons) m.w. GRF materials. GRF appears to be structurally different between species and more than one GRF may be present within the same species. One of the ovine brain peptides with GH-releasing activity was partially characterized as His-Ser-Asp-Gly-Ile-Phe-Thr-Asp-Ser-Tyr- Lys-Arg-Try-Asn-Lys-Glu-Met- Ala-Lys--which is similar to rat GRF and porcine VIP having His at the N-terminus. Another peptide with GRF activity which eluted earlier on reverse phase HPLC and later on cation exchange chromatography has also been obtained in a pure form.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous CCK is not involved in the regulation of interdigestive gastrointestinal and gallbladder motility in conscious dogs.

In this study, we assessed whether endogenous CCK is involved in the regulation of interdigestive gastrointestinal and gallbladder motility in conscious dogs with force transducers chronically implanted in the gastric antrum, duodenum, jejunum and gallbladder. L364718 at a dose of 1.0 mg/kg was used as a specific and potent CCK receptor blocker, and its effect on spontaneous interdigestive motility and plasma motilin release were examined. Additionally, the contractile activity of exogenous synthetic canine motilin (20-100 ng/kg) with or without pretreatment with L364718 at a dose of 1.0 mg/kg was assessed. Whether the blocking effect of L364718 on CCK receptors was sufficient or not was verified by giving CCK-OP at a bolus dose of 10 ng/kg. As a result, cyclic changes in interdigestive motor activity and the plasma motilin concentration were not affected by pretreatment with L364718. L364718 also did not affect motilin-induced interdigestive contractile activity in the gastrointestinal tract and gallbladder. On the other hand, the effect of CCK-OP was completely abolished by pretreatment with L364718. It is concluded that endogenous CCK is not involved in the regulation of spontaneous and motilin-induced interdigestive contractions in the canine gastrointestinal tract and gallbladder.

Effect of nitric oxide synthase inhibition on plasma motilin release in fasted dogs.

Inhibition of nitric oxide (NO) synthase on plasma motilin concentrations is not known. The aim of this study was to examine the effect of NO synthesis inhibitor on gastrointestinal motility and motilin release in conscious dogs. Dogs fitted with force transducers were given N omega-nitro-L-arginine (L-NNA) after the termination of phase III contractions. Blood samples were taken for measurement of motilin concentrations. L-NNA induced phase III-like contractions in the stomach in the duodenum in association with a significant increase in motilin level. Atropine or hexamethonium significantly inhibited L-NNA-induced phase III-like contractions and the increase in motilin level. Atropine or hexamethonium significantly inhibited L-NNA-induced phase III-like contractions and the increase in motilin level. Ondansetron markedly inhibited gastric, but not duodenal, phase III-like contractions without affecting the increase in motilin level caused by L-NNA. Vagotomy affected neither the occurence of phase III-like contractions nor the increase in motilin level produced by L-NNA. We conclude that inhibition of NO synthesis stimulates motilin release via cholinergic pathways independent of the vagus, and induces phase III-like contractions in the stomach and duodenum. Phase III-like contractions induced by L-NNA are mediated through the activation of 5-HT, receptors.

Control of gallbladder contractions by cholecystokinin through cholecystokinin-A receptors in the vagal pathway and gallbladder in the dog.

The mechanism of CCK action on gallbladder contractions in the physiological condition is unclear. Gallbladder contractions were monitored by means of chronically implanted force transducers in conscious dogs. Postprandial gallbladder contractions were partially inhibited by atropine and hexamethonium, and completely inhibited by devazepide. In vitro contractile response of canine gallbladder muscle strips to CCK-8 was also studied. CCK-8-induced muscle strip contraction was atropine and tetrodotoxin resistant, but was completely eliminated by devazepide. The existence of CCK receptors in the vagal nerve and gallbladder was examined by means of autoradiography. Forty-eight hours after ligation of the abdominal vagus, CCK-8 binding sites were found to accumulate in the subdiaphragmatic vagal nerve immediately proximal to the ligature, and similar binding sites were also found in the gallbladder smooth muscle layer. These binding sites were displaced by the addition of 10(-7) mol/1 unlabeled CCK-8 and devazepide, but L-365,260 had no effect. In conclusion, it is considerable that postprandial CCK-induced gallbladder contractions are controlled through CCK-A receptors both on the vagal nerve in stimulating endogenous release of acetylcholine and on the gallbladder directly to stimulate muscle contraction in the dog.

Motilin release by intravenous infusion of nutrients and somatostatin in conscious dogs.

to investigate the regulatory mechanism of motilin release, plasma motilin was measured by radioimmunoassay in healthy dogs during the fasting state and after intravenous administration of various nutrients and somatostatin. The fasting plasma motilin levels of these dogs were found to fluctuate intermittently. Intravenous glucose loading lowered plasma motilin, but immediately after the end of the glucose infusion as abrupt rise of plasma motilin was observed. Mixed amino acids administered intravenously abruptly inhibited motilin secretion, and plasma motilin levels remained low even 45 min after the end of the infusion. On the other hand, no remarkable change in plasma motilin was noted after the fat infusion. Following somatostatin infusion, plasma motilin was significantly decreased, remaining low even 30 min after the end of the infusion. These observations led us to conclude than motilin secretion is regulated by somatostatin and by nutrients coming through intravenous routes.