Antral gastrin- and somatostatin-producing cells and intraluminal peptide secretion in normal subjects and duodenal ulcer patients with and without vagotomy

The behaviour of gastrin (G) cells and somatostatin (D) cells in endoscopic antral biopsies and that of intraluminal gastrin (ILG) and somatostatin (ILS) release in the gastric juice were investigated in three groups of patients: control subjects, duodenal ulcer (DU) patients and DU patients treated by a superselective vagotomy (SSV). G and D cell densities were correlated in the three groups of subjects. The G/D cell ratio was significantly increased in SSV patients (P less than 0.001) as compared to control and DU patients. No correlation was found between gastrin or somatostatin cell densities and basal intraluminal levels of the two peptides. ILG output was significantly higher in DU patients than in control or SSV patients (P less than 0.001). ILS output was also higher in DU patients than in controls (P less than 0.001) and in SSV patients (P less than 0.05). It was also significantly augmented in SSV (P less than 0.001) as compared to control patients. ILG and ILS concentrations were only correlated in controls. Within each of the three groups of subjects, ILG and ILS release varied in function of the gastric juice pH. Our results emphasize the necessity to consider the intragastric pH as well as the physiological or pathological state to study intraluminal peptides in man.     

Variations in the response of salt-stressed Rhizobium strains to betaines

A total of 15 rhizobial strains representing Rhizobium meliloti, Rhizobium japonicum, Rhizobium trifolii, Rhizobium leguminosarum, Rhizobium sp. (Sesbania rostrata) and Rhizobium sp. (Hedysarum coronarium), were studied with regard to growth rate under salt stress in defined liquid media. In the presence of inhibitory concentrations of NaCl, enhancement of growth resulting from added glycine betaine was observed for R. meliloti strains and Rhizobium sp. (Hedysarum coronarium) but not for other Rhizobium species. The concentration of glycine betaine required for maximal growth stimulation was very low (1 mM) in comparison with the osmolarity of the medium. The stimulation was shown to be independent of any specific solutes. Other related compounds like proline betaine, carnitine, choline, -butyrobetaine and pipecolate betaine were also effective compounds in restoring the growth rate of cells grown in medium of elevated osmolarity. High rate of glycine betaine uptake was demonstrated in R. meliloti cells grown in media of increased osmotic strength. The intracellular concentration of this solute was found to be 308 mM in 0.3 M NaCl-grown cells and 17 times lower in minimal medium-grown cells. Glycine betaine was used for growth under conditions of low osmolarity but could not serve as sole carbon or nitrogen source in medium of increased osmotic strength. Experiments with [¹⁴C]glycine betaine showed that this molecule was not metabolized by cells subjected to osmotic stress, whereas it was rapidly converted to dimethylglycine, sarcosine and glycine in minimal medium-grown cells.Abbreviations LAS lactate-aspartate-salts - LGS lactate-glutamate-salts - LS lactate-succinate - MSY mannitol-salts-yeast - YLS yeast-lactate-succinate     

Ontogeny of vasoactive intestinal peptide in the human fetal digestive tract

Immunocytochemistry and radioimmunoassay were used to assess the appearance time and tissue distribution of vasoactive intestinal peptide (VIP) in the digestive tract of the human fetus. By radioimmunoassay, VIP was measurable from 10 weeks of gestation. The peptide was abundantly distributed in the jejuno-ileum and colon, where the tissue peptide concentration rose from 9-14 weeks of gestation (18.4 +/- 4.4 and 22.0 +/- 5.0 pmol/g wet weight, respectively) to 15-21 weeks (83.0 +/- 21.1 and 98.6 +/- 36.4 pmol/g, respectively). Lower concentrations were recorded in pancreas from 9-14 weeks of gestation (4.3 +/- 0.8 pmol/g) to 15-21 weeks (13.9 +/- 3.7 pmol/g). The peptide concentration was 15.6 +/- 1.9 pmol/g in fundus and 25.5 +/- 3.2 pmol/g in antrum from 15 to 21 weeks of gestation. The highest concentration was recorded in duodenum from 15 to 21 weeks of gestation (118.4 +/- 40.8 pmol/g wet weight). Tissue VIP concentration and age were positively correlated in the jejuno-ileum. By immunofluorescence, immunoreactive VIP was localized in nervous fibers in the muscularis externa, in the submucosa and in the lamina propria. Scarce cell bodies were also found in the myenteric plexus. No immunofluorescent endocrine cells were observed. These results suggest: (1) the early appearance of immunoreactive VIP in gut, as early as 10 weeks of gestation; (2) the peptide, localized in nervous structures only, follows the same distribution pattern as that in adults; (3) the development of VIPergic structures is a continuous process, initiated during the 3rd month of pregnancy.     

The use of N-urethane-protected N-carboxyanhydrides (UNCAs) in amino acid and peptide synthesis

N-Urethane-protected N-carboxyanhydrides (UNCAs) are very reactives. They have been successfully used in peptide synthesis, in both solution and solid phase. We have demonstrated that UNCAs are interesting starting materials for the synthesis of various amino acid derivatives. Chemoselective reduction of UNCAs with sodium borohydride led the corresponding N-protected β amino alcohols. Reaction of UNCAs with Meldrum's acid, followed by cyclisation, yielded enantiomerially pure tetramic acid derivatives. Diastereoselective reduction of tetramic acid derivatives produced (4S,5S)-N-alkoxycarbonyl-4-hydroxy-5-alkylpyrrolidin-2-ones derived from amino acids, which after hydrolysis yielded statine and statine analogues. Tetramic acid derivatives could also be obtained by reaction of UNCAs with benzyl ethyl followed by hydrogenolytic deprotection and decarboxylation. UNCAs also reacted with phosphoranes to produce the ketophosphorane in excellent yields. Subsequent oxidation with oxone or with [bis(acetoxy)-iodol]-benzene produced vicinal tricarbonyl derivatives. These reactions usually proceeded smoothly and with high yields.     

Variations of plasma immunoreactive motilin, pancreatic polypeptide, gastrin and somatostatin along the duodenal motility cycle in the pig

The peripheral plasma concentrations of immunoreactive motilin, pancreatic polypeptide (PP), somatostatin and gastrin were measured in 7 pigs fasted to 24 h and subsequently fed a standard meal. Plasma motilin peaked during the last part of phase II activity of the migrating myoelectric complex (MMC) sequence (25.2 +/- 2.3 pM), the lowest value being recorded during phase I (10.6 +/- 1.5 pM) after a 24 h fast. Plasma motilin remained at a low level during the digestive pattern of duodenal activity, no fluctuation occurring when the first postprandial MMC recurred. At variance analysis, gastrin and PP were not released phasically with MMC in the fasting state, while at autocovariance both peptides tended to fluctuate during the MMC sequence with positive and negative peaks at regular intervals along MMC cycles. No variation of plasma somatostatin was observed in the fasting animals. These findings argue against a major role of circulating PP, gastrin and somatostatin-like components in the control of fasted and post absorptive duodenal motility in pigs while the role of motilin remains equivocal.     

Peptide immunocytochemistry in afferent neurons from lower gut in rats

Several peptides were detected in primary sensory neurons located in nodose and dorsal root ganglia and projecting from rat cecum and rectosigmoid, through a combination of retrograde staining by the fluorescent tracer DY-2HCl and of the immunofluorescent procedure of Coons. The three larger cell populations thus identified stored immunoreactive components respectively similar to calcitonin gene-related peptide (CGRP), substance P (SP), and a peptide related to peptide histidine methionine (PHM). The later immunoreactivity consisted of a single molecular form with an apparent molecular weight smaller than PHM itself. Fewer cells contained components immunologically similar to somatostatin 14 (ST14), to the 1-14 N-terminal sequence of somatostatin 28 (1-14 S28), and to neuropeptide Y (NPY). Neonatal treatment with capsaicin resulted in a drastic reduction of immunoreactivity for SP, PHM, ST14, 1-14 S28, and in a partial reduction of CGRP-like positive perikarya. These results demonstrate that several peptides are potentially involved in the sensory innervation of the lower gut in rat.     

Pancreatic secretory response to feeding in the calf: CCK-A receptors, but not CCK-B/gastrin receptors are involved

In bovine species, as in human, the pancreas predominantly expresses cholecystokinin-B (CCK-B)/gastrin receptors. However, the role of this receptor in the regulation of meal-stimulated pancreatic enzyme release has not been determined. In milk-fed calves, we previously described prandial patterns of exocrine pancreatic secretion and a long prefeeding phase was observed. The present study was aimed at determining both the role of external stimuli in the outset of the prefeeding phase and the implication of pancreatic CCK-A and CCK-B/gastrin receptors in the mediation of pancreatic response to feeding. The first objective was studied by suppressing external stimuli associated with food intake (unexpected meal) and the second by infusing highly specific and potent antagonists of CCK-A (SR 27897) and CCK-B/gastrin (PD 135158) receptors during the prandial period. When calves were given an unexpected meal, the long prefeeding increase in pancreatic secretion was absent. SR 27897 (but not PD 135158) inhibited the preprandial phase and greatly reduced postprandial pancreatic juice and enzyme outflows. The expectancy of a meal seemed to elicit an increased pancreatic response right before a meal and CCK-A receptors may mediate this information via neural pathways. The implication of CCK and CCK-A receptors in mediating the postfeeding pancreatic response was also demonstrated. The participation of CCK-B/gastrin receptors in this regulation was not demonstrated.     

Ontogeny of substance P in the digestive tract, spinal cord and hypothalamus of the human fetus

The time of appearance and tissue concentrations of substance P-like immunoreactivity (SP-LI) were studied in 53 human fetuses aged 8-21 weeks. Detectable amounts were present at 8 weeks of gestation in available fragments of spinal cord and intestine. Thereafter, the tissue concentrations were highest in spinal cord, intermediate in hypothalamus and lowest in digestive tract. Except for a significant increase in the intestinal wall, the concentrations did not vary from the 8-14 to the 15-21 week period. At chromatography, SP-LI in extracts of spinal cord and intestine was essentially eluted in the volume of the synthetic undecapeptide. Using the indirect immunofluorescence technique, the localization of SP-LI positive structures in the digestive tract was studied in 5 fetuses aged 12-18 weeks. Scarce cell bodies were observed in the myenteric plexus. Nerve fibers were recognized in the muscular layer, in the myenteric plexus and in connective tissue of pancreas. The present results demonstrate the early appearance of SP-LI positive structures both in central nervous system and in the enteric nervous system in the human fetus. In the age range tested, SP-LI concentrations were noticeably higher in spinal cord and hypothalamus than in the digestive tract.     

Is caseinomacropeptide from milk proteins,an inhibitor of gastric secretion?

The aim of this work was to study, in vivo, the effect of the ingestion of not glycosylated caseinomacropeptide (CMP) on gastric secretion. In Experiments #1 and #2, 7 calves fitted with a gastric pouch received either a diet without CMP (C diet) or C diet in which CMP was introduced (equal to and 5 folds that of CMP quantity contained in cow milk, diets CMP1 and CMP5, respectively). In Experiment #3, 2 calves (with gastric pouch) were fed C diet followed by an “iv perfusion” of CMP. In Experiment #4, 25 calves fed either C, CMP1 or CMP5 diets were fitted with a blood catheter for sample collections. The quantities of daily gastric secretions seemed few modified by CMP ingestion but the profile of these secretions was changed along the day. The most important result is that CMP can inhibit gastric secretions (mainly hydrochloric acid) stimulated by the meal, but there was no dose-dependent response. No similar observations were obtained after perfusion of CMP in jugular vein. CMP was not detected in blood. Results obtained in our experiments are not in favor of its significant intestinal absorption. Gastrin, somatostatin and VIP could be implicated in the mechanisms of regulation.