Inhibitory effect of peptide YY on gastric acid output in rats

Central and peripheral regulation of gastric acid secretion by peptide YY

Peptide YY (PYY) released postprandially from the ileum and colon displays a potent inhibition of cephalic and gastric phases of gastric acid secretion through both central and peripheral mechanisms. To modulate vagal regulation of gastric functions, circulating PYY enters the brain through the area postrema and the nucleus of the solitary tract, where it exerts a stimulatory action through PYY-preferring Y1-like receptors, and an inhibitory action through Y2 receptors. In the gastric mucosa, PYY binds to Y1 receptors in the enterochromaffin-like cells to inhibit gastrin-stimulated histamine release and calcium signaling via a pertussis toxin-sensitive pathway.

Role of circulating peptide YY in the inhibition of gastric acid secretion by dietary fat in humans

BACKGROUND

Intestinal fat inhibits gastric acid secretion and induces release of peptide YY (PYY) into the circulation. The aim of this study was to further establish the role of circulating PYY in the inhibition of gastric acid secretion by intraduodenal fat.

METHODS

Plasma PYY concentrations and gastrin-stimulated gastric acid output were measured in response to intravenous infusion of PYY in eight healthy men. The results were compared with those obtained after intraduodenal administration of dietary fat.

RESULTS

Plasma PYY concentrations increased by 8.1 +/- 1.8 pmol/l (P < 0.005) in response to the lower and by 13.5 +/- 2.5 pmol/l (P < 0.005) in response to the higher PYY dose. These increments were comparable to those observed after intraduodenal fat (10.3 +/- 2.4 pmol/l). Intraduodenal fat significantly inhibited (P < 0.005 versus control) gastrin-stimulated gastric acid secretion by 74% +/- 6%, but neither the lower (3% +/- 7%; NS) nor the higher PYY dose (1% +/- 10%; NS) induced any change in gastric acid output. PYY was biologically active, as reflected by a significant delay (P = 0.04) of orocaecal transit time.

CONCLUSION

Release of PYY into the circulation is not responsible for inhibition of gastrin-stimulated gastric acid secretion by dietary fat.

Release of peptide YY and inhibition of gastric acid secretion by long-chain and medium-chain triglycerides but not by sucrose polyester in men

METHODS

In the present study, we have investigated the effects of intraduodenal perfusion of long-chain and medium-chain triglycerides and of sucrose polyester on the release of peptide YY in healthy men.

RESULTS

Perfusion of medium-chain triglycerides (180 mmol fatty acids) increased the plasma concentration of peptide YY from 7.9 pmol L(-1) (SEM 0.2, n=8) to 10.7 pmol L(-1) (SEM 0.5, n=8), whereas perfusion of long-chain triglycerides (180 mmol fatty acids) had a significantly greater effect, increasing peptide YY concentration from 8 6 pmol L(-1) (SEM 0.2, n=8) to 18.9 pmol L(-1) (SEM 2.4, n=8, P < 0.008). A smaller quantity of long-chain triglycerides (90 mmol fatty acids) increased plasma concentration of peptide YY from 7.4 pmol L(-1) (SEM 0.4, n=8) to 13.3 pmol L(-1) (SEM 1.5, n=8), whereas sucrose polyester (90 mmol fatty acids) did not change peptide YY concentration. In a previous study, we investigated gastrin-stimulated gastric acid output in response to these treatments. The correlation between increases in peptide YY in response to all treatments and the decrease in acid output was r=0.72 (n=48, P < 0.0001). These results show that both long-chain and medium-chain triglycerides, but not sucrose polyester, stimulate the release of peptide YY.

CONCLUSION

We speculate that peptide YY may play an important role in the inhibition of gastrin-stimulated gastric acid secretion by long-chain and medium-chain triglycerides.

Peptide YY release after intraduodenal, intraileal, and intracolonic administration of nutrients in rats

Peptide YY (PYY) release was studied by measuring radioimmunoassayable PYY in the arterial plasma of anaesthetized rats receiving into the duodenum, ileum or colon either a complete semi-liquid meal (3ml, 21kJ) or elemental nutrients as isocaloric or isoosmolar solutions. PYY release induced by the intraduodenal meal peaked at 60min and lasted more than 120min. The integrated response of PYY over 120min was larger when the meal was administered into the duodenum than into the ileum. The undigested meal induced no release of PYY over a 120-min period when administered into the colon. When injected into the duodenum in isocaloric amounts to the meal, glucose and amino acids led to the release of as much PYY as did the meal, whereas oleic acid led to the release of less PYY. Part of these responses were due to osmolarity, since administration of intraduodenal hyperosmolar saline led to the release of about half as much PYY as did hyperosmolar glucose. In moderate amounts, and injected as a solution isoosmolar to plasma, oleic acid was a major PYY releaser; the amounts released were at least two times larger when oleic acid was administered into the duodenum than into the ileum and colon. Isoosmolar glucose and amino acids led to the release of no PYY when injected into the duodenum, but were nearly as active as oleic acid in the colon. Short-chain fatty acids induced the release of PYY when injected into the colon, but not into the ileum. Hexamethonium suppressed PYY release induced by the intraduodenal meal, but did not change PYY release induced by glucose or oleic acid in the colon. Urethane anaesthesia did not reduce PYY release induced by the intraduodenal meal. These results suggest that two mechanisms at least contribute to PYY release in the rat. An indirect, neural mechanism, involving nicotinic synapses, is prominent in the proximal small intestine; the stimulation is transmitted to ileal and colonic L-cells by undetermined pathways, but contact of nutrients with L-cells is not needed. Another mechanism, probably direct and quantitatively smaller, occurs in the distal intestine when nutrients come into contact with the mucosa containing L-cells. Glucose, fatty acids and amino acids stimulate differentially the proximal and distal mechanisms.

The effect of duodenojejunal alimentation on gastric pH and hormones in intensive care unit patients

We evaluated effects of duodenojejunal (DJ) feeding on gastric pH and selected gastrointestinal hormones in 13 randomly selected patients in an intensive care unit (ICU). To obtain baseline values for gastric pH, a nasogastric (NG) tube was placed in each patient and gastric pH was measured every 30 minutes for 2 hours. To obtain control values, a Dobbhoff tube was placed fluoroscopically and 0.45 percent saline solution (NaCl), 75 ml, was infused for 1 hour and gastric pH was measured again; the previously placed NG tube was left in position. Then, by randomization, either 0.45 percent NaCl (pH = 5) was continued (n = 6) or a high-nitrogen, isotonic, enteral feeding solution (Osmolite HN, pH = 6.4) (n = 7) was infused, both at 75 ml/h. Gastric pH was noted hourly for 96 hours; antacid (Maalox TC, 15-ml aliquots) was given by NG tube when the pH was 4 or less. After 96 hours, the infusion was stopped and gastric pH was noted for 4 additional hours. Before and during initial saline solution infusion; after 24, 48, 72, and 96 hours of continuous infusion; and 4 hours after stopping the infusion, peripheral venous blood was obtained for measurement of plasma gastric inhibitory polypeptide (GIP) and serum gastrin. Data were analyzed by ANOVA (RMD), Fishers' exact test, and the unpaired t-test. Groups did not differ demographically. Throughout the infusion, gastric pH tended to be higher with the enteral feeding solution than with saline solution, but this was significant only at 24 hours. Less antacid was required with the enteral feeding solution at 24 and 48 hours than with saline solution. Plasma GIP levels were significantly higher with the enteral feeding solution than with saline solution during most of the infusion. Serum gastrin levels did not differ between the groups. In this cohort, infusion of the enteral feeding solution tended to maintain a gastric pH of more than 4 and was associated with increased plasma GIP levels, which may inhibit gastric acid secretion. Early enteral feeding may benefit certain ICU patients.

Absorption of oral mesalazine-containing preparations and the influence of famotidine on the absorption

The mesalazine-containing preparations Asacol, Pentasa, and Salofalk (=Claversal) are frequently used in the treatment of inflammatory bowel disease. The release patterns of these formulations are time- and/or pH-dependent. The aim of this study was to investigate the patterns of absorption of these preparations and the influence of raised intragastric pH on absorption. Gastric pH was raised by simultaneous administration of famotidine. Absorption was determined by assaying with a high-performance liquid chromatography method the urinary excretion of acetylmesalazine, the major metabolite of mesalazine. A large intra- and inter-individual variability in absorption was found for all three formulations, both with and without concomitant famotidine administration. Asacol and Pentasa were significantly less absorbed than Salofalk. A significant lower absorption of mesalazine was seen when Asacol was combined with famotidine. Variations in gastric pH have negligible effect on the bioavailability of mesalazine in vivo.