Kae Yol Lee

Radioimmunoassay of motilin. Validation and studies on the relationship between plasma motilin and interdigestive myoelectric activity of the duodenum of dog.

A radioimmunoassay method of motilin was developed in our laboratory and was validated in dogs with a platinum monopolar electrode in the duodenum. We confirmed that a bolus infusion of 0.3 M tris-buffer solution or 0.1 N HCl solution in the duodenum produces a significant rise in plasma immunoreactive motilin (IRM) concentrations. This coincided with a marked increase in the percentage of spike potentials on slow waves of the duodenum, similar to phase III of interdigestive myoelectric-activity (MA). A possible relationship between plasma IRM and interdigestive MA of canine duodenum was studied. It was found that cyclic changes occurred in the fasting plasma IRM concentrations in dogs. While the peak motilin concentration was always observed in phase III, the lowest concentration of motilin was found in phase I of interdigestive MA in the duodenum. In dogs with the electrodes in the duodenum and jejunum, the peak IRM concentration did not correlate with phase III of interdigestive MA in the jejunum. A dose of synthetic porcine motilin, 0.06 μg/kg/hr, which produced the plasma IRM concentration comparable to the peak fasting motilin concentration, could induce an identical phase III in the duodenum. These observations indicate that there is a relationship between cyclic changes in plasma IRM concentrations and interdigestive MA of the duodenum. It is suggested further that motilin is a hormone which may play an important role in inducing phase III of interdigestive MA in the duodenum.

Cholinergic role on release and action of motilin

In conscious dogs with gastric fistula and platinum electrodes on the antrum, duodenum and jejunum, IV atropine 100 micrograms/kg/hr and hexamethonium 10 mg/kg/hr, blocked cyclic increases in fasting plasma motilin concentration (PMC) and spontaneous migrating myoelectric complexes (MMCs) of both antrum and duodenum. The two drugs also blocked occurrence of premature MMCs produced by synthetic porcine motilin. In anesthetized dogs, electrical stimulation of cervical vagi with stimulation parameters: 9 V, 10 c/s, 5 msec, caused a significant increase in both portal and femoral venous PMC which was blocked by atropine. Fractionations of vagus nerve extracts by gel filtration using Sephadex G-50 superfine column revealed most of motilin-like immunoreactivity (MLI) with the same mobility as pure porcine motilin. Studies suggest that cholinergic influence plays a significant role on release of motilin.

Pituitary adenylate cyclase-activating peptide stimulates rat pancreatic secretion via secretin and cholecystokinin releases☆☆☆

BACKGROUND & AIMS Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates protein and/or amylase secretion from isolated rat pancreatic acini. The effect of PACAP on pancreatic secretion in vivo and its mechanism of action were studied. METHODS Rats were prepared with pancreatic duct cannulation, pyloric ligation, and bile diversion into duodenum, and 2.5, 5, and 10 nmol/kg PACAP-27 was administered intravenously while pancreatic juice was collected for 30 minutes. In other groups of rats, the effect of 10 nmol/kg PACAP-27 was studied under the influence of either atropine; loxiglumide, an antisecretin serum; a combination of both loxiglumide and the antiserum; or a PACAP antagonist (PACAP 6-38). Plasma secretin and cholecystokinin concentrations were measured by radioimmunoassay. RESULTS (1) PACAP dose-dependently increased pancreatic secretion of fluid, bicarbonate, and protein; (2) the increase in pancreatic secretion paralleled that of plasma secretin and cholecystokinin; (3) a combination of loxiglumide and antisecretin serum eliminated the PACAP-stimulated pancreatic secretion, whereas loxiglumide or antisecretin serum alone partially but significantly blocked pancreatic secretion; (4) atropine failed to influence PACAP-induced pancreatic secretion; and (5) PACAP antagonist profoundly suppressed the PACAP action. CONCLUSIONS PACAP-27 dose-dependently stimulates pancreatic secretion of fluid, bicarbonate, and protein in rats. This effect is mediated by release of both secretin and cholecystokinin and is independent of cholinergic tone.

Studies on Mechanism of Retching and Vomiting in Dogs Effect of Peripheral Dopamine Blocker on Myoelectric Changes in Antrum and Upper Small Intestine

In five conscious dogs prepared with a gastric cannula and platinum monopolar electrodes in the antrum, duodenum, and jejunum, the effect of dopamine or copper sulfate on the myoelectric activity was studied. During phase 1 of interdigestive myoelectric activity, retching, and/or vomiting occurred in 1.6±0.2 (mean±se) min after intravenous bolus injection of dopamine (50 μg/kg) or in 8.7±1.8 min after intragastric administration of copper sulfate (2%, 50 mg). Immediately prior to the retching and/or vomiting act, a group of disordered myoelectric activities occurred, including retrogrademoving trains of spike activity starting from the jejunum and the subsequent tachyarrhythmia in the antrum. These motility changes also occurred in the two anesthetized dogs so studied. Both the retching and/or vomiting act and the abnormal myoelectric activity which were induced by dopamine and by copper sulfate were prevented by intravenous administration of a peripheral dopamine blocker, domperidone, 5 mg, in 100% and 70%, respectively. Although domperidone could not prevent the retching and/or vomiting induced by copper sulfate in three of 10 experiments, it delayed the onset of vomiting from 8.7±1.8 to 14.5±5.3 min. A possible role of peripheral dopamine receptor on the motility disorders associated with retching and/or vomiting has been suggested.

Effect of electrical stimulation of the vagus on plasma motilin concentration in dog

Abstract Ten dogs anesthetized with α-chloralose were prepared with platinum monopolar electrodes in the antrum, duodenum and jejunum to record myoelectrical activity and bipolar stimulating electrodes placed on distal cut end of both cervical vagi to apply electric stimulation. Blood samples were obtained from both portal and femoral veins before and after bilateral vagal stimulation was initiated while the myoelectric activity was recorded continuously. The stimulation parameters used were low frequency (9V, 5 cps, 0.5 ms) and high frequency stimulus (9V, 30 cps, 10 ms) for 10 min. During the stimulation, plasma motilin concentrations increased significantly in both portal and femoral veins with simultaneous increases in the spike activity. The increment in the motilin level of portal venous blood was more marked. In 7 dogs, high frequency stimulation was repeated while the animals received i.v. atropine, 100 μg/kg-hr. Atropinization completely blocked the increase in the motilin concentration in response to high frequency stimulus with a simultaneous inhibition of the spike activity. The study suggests strongly that the vagus nerve plays an important role on endogenous release of motilin through its cholinergic pathway.

Purification of two secretin-releasing peptides structurally related to phospholipase A2 from canine pancreatic juice.

We previously showed that canine pancreatic juice contains a secretin-releasing factor activity. In this study, we carried out isolation of two secretin-releasing peptides (SRPs) from canine pancreatic juice. Through ultrafiltration, anion and cation exchange, and reverse-phase high-performance liquid chromatography (HPLC) steps and an in vitro bioassay in STC-1 cells, two SRPs, SRP-1 and SRP-2, were isolated and purified to homogeneity. Both SRPs dose-dependently stimulated secretin release from STC-1 cells. The results of mass spectral analysis indicated that SRP-1 and SRP-2 had molecular masses of 14,061 Da and 14,053 Da, respectively. N-terminal amino acid sequence analysis indicated that SRP-1 was identical to canine pancreatic PLA2 in the 25 residues determined; whereas SRP-2 had 71% sequence homology to the enzyme in the first 21 residues. Commercially available porcine pancreatic PLA2 dose-dependently stimulated secretin release from STC-1 cells. Porcine pancreatic PLA2 also stimulated secretin release from a secretin-producing cells-enriched preparation isolated from rat duodenal mucosa. These results suggest that pancreatic PLA2 and its related peptide may participate in regulation of secretin secretion.

Canine vagus nerve stores cholecystokinin-58 and -8 but releases only cholecystokinin-8 upon electrical vagal stimulation

Cholecystokinin-58 has been shown to be the major form of cholecystokinin (CCK) released to the circulation upon lumenal stimulation of the small intestine in humans and dogs. In anesthetized dogs, electrical vagal stimulation evokes pancreatic exocrine secretion that is in part mediated through the release of CCK. We studied the molecular form of CCK stored in canine vagus nerves and that released into circulation upon electrical vagal stimulation. Gel filtration and radioimmunoassay of the water and acid extracts of canine vagus nerves indicated CCK-8 (35%) and CCK-58 (65%) as the major molecular forms in the vagus nerve. Both forms of CCK isolated from the vagal extracts were equally bioactive as the standard CCK-8 and CCK-58, respectively, in stimulation of amylase release from isolated rat pancreatic acini. Analysis of plasma collected after electrical vagal stimulation indicated that CCK-8 is the only form released into the circulation. The release of CCK-8 upon electrical vagal stimulation was not affected by application of lidocaine to the upper small intestinal mucosa, suggesting that it was released from vagal nerve terminals.

A Non-Gastrin Secretogogue in Ulcerogenic Tumors of the Pancreas

In 18 patients with hypersecretion of acid, severe ulcer diathesis, and pancreatic islet cell tumor or hyperplasia, 14 had hypergastrinemia and 4 had normal plasma gastrin concentration. The neoplasms contained several gut peptides beside gastrin. The immunoreactive gastrin in the tumor extracts measured less than 7 ng/g, less than the amount previously reported. The extracts of each patients tumor also contained a secretogogue other than gastrin that stimulated gastric acid secretion in rats. In addition, the plasma extracts of 2 patients also contained a secretogogue that stimulated acid secretion. After surgical resection of a recurrent metastatic tumor in 1 patient, basal acid secretion decreased from 13.9 to less than 1 meq/h, and the bioactivity of the plasma disappeared. These observations suggest the existence of a secretogogue that appears to be a protein in the pancreatic tumors of some patients with severe ulcer diathesis and hypersecretion.

Roles of the vagus in endogenous release of secretin and exocrine pancreatic secretion in dog.

It has been well established that secretin1 is released from upper small intestinal mucosa in response to hydrogen ion delivered in the duodenum in man 2 and dog.3 As pH of the proximal duodenum decreased below 4.0 during the postprandial period, plasma secretin concentration increased significantly in man.4 We investigated a possible role of the vagus nerve in release of endogenous secretin in conscious dogs as well as anesthetized dogs.

Development of isolated perfused whole stomach for motility study in rat and cat.

An isolatedex vivo perfused mammalian stomach preparation is an ideal model for the study of motility avoiding central nervous influence and circulating humoral factors. In this paper, we describe the technique of such preparation in two different species: rat and cat, and its implication for motility study. While the isolated stomach was perfused with Krebs-Ringer solution via celiac artery, motility of the antrum was recorded using an open-tip tube in rats and a bipolar platinum electrode and a strain gauge in cats. The spontaneous antral motility and its response to drugs, such as dopamine and domperidone proved that the preparation would be a useful model to study motility devoid of influences of the central nervous system and circulating humoral agents.