Comparative Assessment of Secretin and Motilin Responses to Graded Duodenal Acidification in Anaesthetised Pigs

Abstract

The effects of graded duodenal acidification on plasma concentration of immunoreactive secretin, and motilin in portal vein (PV) and carotid artery (CA) were investigated in 6 anaesthetised pigs in which the proximal duodenum was excluded and sequentially irrigated with isotonic saline (pH 7.0) and with hydrochloric acid (HC1) delivered at successive rates of 2, 8 and 40 mM H⁺/40 min(pH of 2.8, 1.9 and 1.0, respectively) under a constant flow of 10 ml/min. The release of secretin was first observed at pH 1.9 (from basal 4.2 ± 0.3 to a peak of 26.6 ± 9.8 pM in PV and from 3.4 ± 0.3 to 6.8 ± 0.9 pM in CA) and further increased at pH 1.0 (peaks of 60.9 ± 16.3 in PV and 16.8 ± 2.6 pM in CA). In contrast, only the highest HC1 concentration (pH of effluent: 1.0) induced significant increases of plasma motilin (PV: peak of 25.2 ± 4.9 for basal 13.3 ± 1.1 pM, CA: 14.3 ± 2.4 for basal 10.5 ± 0.6 pM). A sharp decrease of the plasma secretin and motilin concentration was observed when the venous drainage of the duodenal segment was occluded, followed by a rapid increase when the clamp was released. In the present experimental conditions, duodenal motilin-producing sites were less sensitive to graded luminal acidification than secretin cells. Thus, the release of duodenal motilin in response to variations of luminal pH may be expected to occur primarily from the most proximal part of the duodenum in physiological conditions.

Regulation of Motilin Release from Isolated Perfused Pig Duodenum

“…Our data clearly indicate that the presence of bile in the duodenum may cause a motilin release. This indicates that emptying of the gallbladder may play an important role in the motilin release ob served in relation to ingestion of a meal [30,40], Acidification of the duodenum as a stimulating factor for motilin release has been reported by several groups, Motilin Release from the Pig Duodenum for instance Bloom et al [33] in man, Cuberet al [41] in pig, and our results support this view. Thus, emptying of low pH chyme from the stomach into the duodenum may also be an important factor for the motilin release ob served in relation to a meal.…”

Forty years of achievement in french research on digestive physiology in the pig

“…The acidification of the proximal duodenum was previously shown to induce the release of secretin and motilin in anaesthetised pigs [43]. A temporal relationship was evidenced in conscious fasting pigs between the successive phases of MMC and the cyclical variation of plasma motilin, pancreatic polypeptide, and gastrin, but not somatostatin [42,44].…”

“…Later on, several regulatory peptides such as motilin, cholecystokinin, secretin, pancreatic polypeptide, neurotensin, etc., were also shown to play an important role in the control of gastrointestinal motility [42,43] and digestive secretions [45,46,85,86,120]. Moreover, Rérat et al [158] showed that an increase in the level of proteins in the diet induced large changes in the hormonal purified proteins, e.g.…”

Biliary and pancreatic secretory component of the migrating myoelectric complex in the pig. Effect on intraduodenal pH

“…Cyclical variations in the plasma levels of motilin (Cuber, Laplace and Chayvialle, 1984), cholecystokinin (Cuber et al, 1986a), gastrin and pancreatic polypeptide (Cuber et al, 1986b) with a periodicity closely related to that of the MMC were recently described in the pig. Results obtained in pigs also suggest that the acidification may lead to a growing release of various peptides such as secretin (Cuber et al, 1985). The occurrence of a pH close to neutrality during early RSA may interrupt this release and could account for the rapid decrease in biliary and pancreatic flow rates.…”