Plasma Immunoreactive Motilin Concentration Research Articles

Circadian variations in plasma immunoreactive motilin concentrations

Circadian variations in plasma immunoreactive motilin concentrations

Interdigestive Gallbladder Bile Concentration in Relation to Periodic Contraction of Gallbladder in the Dog

Interdigestive changes in the concentration of bilirubin and sodium in gallbladder bile collected through a chronically indwelling tube in the gallbladder were measured in conjunction with periodic contractions of the gallbladder and immunoreactive motilin concentration in plasma in conscious dogs. It was found that the bilirubin concentration in the gallbladder bile increased as stepped arcs that show periodic decreases with each cycle of the interdigestive migrating contraction in the stomach. The cycle for bilirubin concentration was then repeated, with higher maximum bilirubin values occurring during successive interdigestive migrating contractions cycles. In contrast, the sodium concentration did not progressively increase but fluctuated widely in association with changes in the bilirubin concentration. Peaks in the concentration of bilirubin and sodium generally coincided and occurred in the phase 3 period of the interdigestive migrating contractions in the stomach and the duodenum. However, the initial rise in the sodium concentration after the fall took place earlier than that in the bilirubin concentration in almost one-half of all experiments. Peaks of plasma immunoreactive motilin concentration coincided with the maximum concentration of gallbladder bile in each of the concentrating cycles, but there was no correlation between the two when compared over the entire period of the experiments. These findings suggest that the interdigestive periodic contractions in the gallbladder may play a role in the progressive concentration of bilirubin in gall bladder bile; that is, gallbladder relaxation after termination of the immunoreactive motilin concentration may be associated with aspiration by the gallbladder of dilute hepatic bile. This may in turn stimulate further gallbladder reabsorption. These studies do not allow firm conclusions to be drawn regarding the role of motilin in gallbladder absorption.

Neurohormonal control of gastrointestinal motor activity in conscious dogs

Interdigestive migrating contractions (IMC) were analyzed for their occurrence interval, duration, migrating velocity, and frequency 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 Thiry 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).

Studies on plasma motilin concentration and interdigestive motility of the duodenum in humans

Plasma immunoreactive motilin concentration (PIMC) was determined at frequent intervals for 4 hr or longer while duodenal motility was recorded by a continuous perfusion technique in 10 fasting healthy volunteers. There were typical interdigestive motor activities including phase I, II, III, and IV in the recordings of duodenal motility from 10 volunteers. Plasma immunoreactive motilin concentration was the lowest at the beginning of phase I, progressively rose during phase II, and reached a peak at the end of phase II. It declined steadily during phases III and IV to return to the lowest value of phase I. The mean PIMC in each phase of duodenal motility was 63.4 ± 4.5, 102 ± 5.0, 82.3 ± 3.1 pg/ml during phase I and IV, and phase II and III, respectively. Plasma immunoreactive motilin concentration in the second half of phase II, 120 ± 6.5 pg/ml, was significantly higher than that of the first half of phase II, 81.4 ± 4.2 pg/ ml. The effect of intravenous atropine sulfate on PIMC and the interdigestive motor activity was studied in 6 volunteers. Atropine sulfate given in a dose of 26.7 μg/kg body wt at the beginning of phase II not only abolished cyclic changes of interdigestive motor activity to produce phase I activity, but also lowered the PIMC to 60.8 ± 8.3 pg/ml. These observations indicate that, like in the dog, there is a close relationship between PIMC and interdigestive motor activity similar to humans. Furthermore, this cyclic change in PIMC appears to be controlled by a cholinergic influence.

Regular and irregular cycles of interdigestive contractions in the stomach.

We have previously reported that during the interdigestive state repeated episodes of high-amplitude contractions interrupted by long-lasting motor quiescence were seen to occur regularly until the next meal in the dog. However, none of the dogs used in our laboratory showed such regular changes in gastric motor pattern all the time during the interdigestive state. In the present study, we measured plasma motilin concentrations and intraduodenal pH together with gastric motor activity in conscious dogs. It was found that as long as intraduodenal pH remained between 7.0 and 8.5 the regular occurrence of the interdigestive contractions was closely associated with increases in the plasma immunoreactive motilin (IRM) concentration. However, when intraduodenal pH became acid, there were no typical interdigestive contractions even though plasma IRM concentration was elevated. We consider that high-amplitude contractions like the interdigestive contractions could not be evoked in the acid-secreting stomach even if the plasma IRM concentration was elevated during the interdigestive state. Acid secretion during the fasted state, the cause of which is not known, seems to be one of the main factors in disturbing the regularity of the interdigestive motor pattern.

Actions of motilin on gastrointestinal motility and plasma immunoreactive motilin concentration in interdigestive and postprandial states.

Among biological actions of motilin on gastrointestinal motility, its action to induce phase III, activity front, of interdigestive myoelectric complex (IMC) appears to be of physiological significance. Synthetic motilin in a dose as little as 0.06 microgram/kg-h was shown to induce phase III in dog. A cyclic increase in fasting plasma immunoreactive motilin concentration (PIMC) occurred in phase III in dog and in a later part of phase II in man, suggesting strongly that there is an intimate relationship between cyclic increase in fasting PIMC and IMC. The observation also suggested that gastric acid secretion increases in phase II and phase III of IMC. The cyclic increase in the acid secretion may be related to a coincidental cyclic increase in PIMC. Ingestion of a meat meal results in a significant decrease in PIMC and abolishes the cyclic increase in PIMC, while IMC changes to digestive pattern after a meal. The significant decrease in PIMC is not attributed to the 3 known gut hormones including gastrin, octapeptide of CCK and secretin.

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.