PACAP and VIP inhibit pyloric muscle through VIP/PACAP-preferring receptors

Secretin effects on gastric functions, hormones and symptoms in functional dyspepsia and health: randomized crossover trial

Abnormal gastric accommodation (GA) and gastric emptying contribute to pathophysiology in functional dyspepsia (FD). Secretin is a key regulator of GA in animal studies. Our aim was to study the effects of secretin on gastric motility, satiation, postprandial symptoms, and key hormones. We performed two double-blind, randomized, saline-controlled crossover trials in 10 healthy volunteers and 10 patients with FD by Rome IV criteria. We used measured GA (by validated SPECT method) after a ¹¹¹In radiolabeled Ensure 300-mL meal and quantified gastric emptying for 30 min by scintigraphy. Satiation was measured by volume to fullness (VTF) and maximum tolerated volume (MTV) on an Ensure nutrient drink test and postprandial symptoms 30 min post-MTV. Fasting and postprandial GLP-1, GIP, and HPP were measured. The ages and sex distribution of healthy controls and patients with FD were similar. Compared with placebo, secretin delayed gastric emptying at 30 min in both health [-11% (-16, -4), P = 0.004]; and FD [-8% (-9, 0), P = 0.03]. Satiation (VTF and MTV), GA, and plasma levels of GLP-1, GIP, and HPP did not differ between treatment arms in health or FD. On ANCOVA analysis (adjusting for age and sex), secretin did not consistently increase postprandial symptoms in health or FD. Secretin delayed gastric emptying in both health and FD without significantly altering GA, VTF, or MTV or selected hormones. Thus, secretin receptor activation may provide a novel therapeutic mechanism for patients with FD and rapid gastric emptying.NEW & NOTEWORTHY The naturally occurring hormone secretin retards gastric emptying of solids without deleteriously affecting gastric accommodation, satiation, other upper gastrointestinal hormones, or postprandial symptoms. Given these findings, a subset of patients with rapid gastric emptying (e.g., the estimated 20% of patients with functional dyspepsia) could be candidates for treatments that stimulate a secretin receptor such as sacubitril, which inhibits neprilysin, an enzyme that degrades secretin.

Presence and Effects of Pituitary Adenylate Cyclase Activating Polypeptide Under Physiological and Pathological Conditions in the Stomach

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide with widespread occurrence throughout the body including the gastrointestinal system. In the small and large intestine, effects of PACAP on cell proliferation, secretion, motility, gut immunology and blood flow, as well as its importance in bowel inflammatory reactions and cancer development have been shown and reviewed earlier. However, no current review is available on the actions of PACAP in the stomach in spite of numerous data published on the gastric presence and actions of the peptide. Therefore, the aim of the present review is to summarize currently available data on the distribution and effects of PACAP in the stomach. We review data on the localization of PACAP and its receptors in the stomach wall of various mammalian and non-mammalian species, we then give an overview on PACAP's effects on secretion of gastric acid and various hormones. Effects on cell proliferation, differentiation, blood flow and gastric motility are also reviewed. Finally, we outline PACAP's involvement and changes in various human pathological conditions.

Pituitary Adenylate Cyclase-activating Polypeptide Inhibits Pacemaker Activity of Colonic Interstitial Cells of Cajal

This study aimed to investigate the effect of pituitary adenylate cyclase-activating peptide (PACAP) on the pacemaker activity of interstitial cells of Cajal (ICC) in mouse colon and to identify the underlying mechanisms of PACAP action. Spontaneous pacemaker activity of colonic ICC and the effects of PACAP were studied using electrophysiological recordings. Exogenously applied PACAP induced hyperpolarization of the cell membrane and inhibited pacemaker frequency in a dose-dependent manner (from 0.1 nM to 100 nM). To investigate cyclic AMP (cAMP) involvement in the effects of PACAP on ICC, SQ-22536 (an inhibitor of adenylate cyclase) and cell-permeable 8-bromo-cAMP were used. SQ-22536 decreased the frequency of pacemaker potentials, and cell-permeable 8-bromo-cAMP increased the frequency of pacemaker potentials. The effects of SQ-22536 on pacemaker potential frequency and membrane hyperpolarization were rescued by co-treatment with glibenclamide (an ATP-sensitive K(+) channel blocker). However, neither N (G)-nitro-L-arginine methyl ester (L-NAME, a competitive inhibitor of NO synthase) nor 1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) had any effect on PACAP-induced activity. In conclusion, this study describes the effects of PACAP on ICC in the mouse colon. PACAP inhibited the pacemaker activity of ICC by acting through ATP-sensitive K(+) channels. These results provide evidence of a physiological role for PACAP in regulating gastrointestinal (GI) motility through the modulation of ICC activity.

Pathogenesis of achalasia cardia

Achalasia cardia is one of the common causes of motor dysphagia. Though the disease was first described more than 300 years ago, exact pathogenesis of this condition still remains enigmatic. Pathophysiologically, achalasia cardia is caused by loss of inhibitory ganglion in the myenteric plexus of the esophagus. In the initial stage, degeneration of inhibitory nerves in the esophagus results in unopposed action of excitatory neurotransmitters such as acetylcholine, resulting in high amplitude non-peristaltic contractions (vigorous achalasia); progressive loss of cholinergic neurons over time results in dilation and low amplitude simultaneous contractions in the esophageal body (classic achalasia). Since the initial description, several studies have attempted to explore initiating agents that may cause the disease, such as viral infection, other environmental factors, autoimmunity, and genetic factors. Though Chagas disease, which mimics achalasia, is caused by an infective agent, available evidence suggests that infection may not be an independent cause of primary achalasia. A genetic basis for achalasia is supported by reports showing occurrence of disease in monozygotic twins, siblings and other first-degree relatives and occurrence in association with other genetic diseases such as Down’s syndrome and Parkinson’s disease. Polymorphisms in genes encoding for nitric oxide synthase, receptors for vasoactive intestinal peptide, interleukin 23 and the ALADIN gene have been reported. However, studies on larger numbers of patients and controls from different ethnic groups are needed before definite conclusions can be obtained. Currently, the disease is believed to be multi-factorial, with autoimmune mechanisms triggered by infection in a genetically predisposed individual leading to degeneration of inhibitory ganglia in the wall of the esophagus.

The gastrointestinal effects that may follow the administration of theophylline reflect the pharmacodynamic profiles of both the parent drug and its metabolites

This study investigates the effect of theophylline along the rabbit gastrointestinal tract in comparison with the pharmacodynamic effect produced by the combined application of its three major metabolites. At concentrations up to 10(-3) m, theophylline relaxed, in a declining order from the lower oesophageal sphincter (LOS) to pylorus, all regions of the upper gastrointestinal tract, but only the ascending colon from the intestinal regions studied. At concentrations higher than 10(-3) m, instead of relaxing, theophylline strongly contracted the antrum and pylorus. In all three small intestinal regions, at concentrations up to 10(-3) m, theophylline produced a weak contraction, which at higher concentrations became very strong, and at 10(-2) m was comparable to that produced by a supramaximal dose of acetylcholine. The additive relaxing effect resulting from the combined application of the theophylline's metabolites was, from oesophagus to pylorus, weaker than that produced by theophylline, while on the ascending colon it was comparable to that of the parent drug. In contrast, the additive contractile effect of the metabolites on the three small intestinal regions was four to five times higher the one produced by theophylline. In conclusion, this study shows that the additive effect of the combined application of theophylline's major metabolites on the rabbit gastrointestinal tract plays a major role in the final response of the intestine, and a minor one in the final responses of the gastric regions, while both the parent drug and the metabolites contribute to the final responses of the oesophagus and LOS.

Age-dependent association of idiopathic achalasia with vasoactive intestinal peptide receptor 1 gene

Idiopathic achalasia is a rare disorder of the oesophagus of unknown aetio-pathogenesis characterized by a myenteric inflammation, aperistalsis and insufficient lower oesophageal sphincter relaxation. Vasoactive intestinal peptide (VIP), present in the myenteric plexus, is involved in smooth muscle relaxation and acts as an anti-inflammatory cytokine. The human VIP receptor 1 gene (VIPR1) is highly polymorphic and may play a role in idiopathic achalasia. One hundred and four consecutive patients and 300 random controls from the same geographic area were typed for five SNPs mapping in the VIPR1 gene. Patients with idiopathic achalasia show a significant difference in allele, genotype and phenotype distribution of SNP rs437876 mapping in intron 4. This association, however, was almost entirely due to the group of patients with late disease onset (P = 0.0005). These results strongly suggest that idiopathic achalasia is a heterogeneous disease with a different aetiology in cases with early or late disease onset.

Relaxing and contracting effects of theophylline's metabolites on the rabbit upper gastrointestinal tract

The present study, aimed to clarify whether the gastrointestinal adverse effects following administration of the bronchodilator theophylline are owing to the action of the drug itself or its metabolites, investigates the pharmacodymanic effects of theophylline's metabolites on the spontaneous contractility in the rabbit upper gastrointestinal tract. Comparative examination reveals that while two of the metabolites, namely 1-methylxanthine (1-MX) and 3-methylxanthine (3-MX), cause a similar, but less pronounced than the parent drug, concentration-dependent relaxation on the isolated oesophagus, lower oesophageal sphincter (LOS), fundus, antrum and pylorus, the remaining two metabolites, 1,3-dimethyluric acid (1,3-DMU) and 1-methyluric acid (1-MU), produce either a weak stimulating effect, or an even weaker relaxation. The relaxation which is muscle-mediated, non-adrenergic non-cholinergic (NANC) and nitric oxide (NO)-independent is probably mediated via inhibition of the metabolites on phosphodiesterases (PDEs), while a presynaptic cholinergic pathway is involved in the weak stimulating effect. The effects of all substances are additive. As a consequence, the net result of the cumulative action of all metabolites in the oesophagus, LOS, antrum and pylorus is, at 10(-3) m, comparable with that of theophylline, but in the fundus it is lower than that of the parent drug, because in the latter tissue the stimulating effect of 1,3-DMU and 1-MU counteracts the relaxing effect of the other two metabolites. However, combination of the parent drug with its metabolites leads to a considerable relaxation in all the gastrointestinal regions extending from the oesophagus to pylorus. Conclusively, upper gastrointestinal adverse effects following theophylline's administration are also because of theophylline's metabolites.

Role of vagus nerve in postprandial antropyloric coordination in conscious dogs

It is generally believed that gastric emptying of solids is regulated by a coordinated motor pattern between the antrum and pylorus. We studied the role of the vagus nerve in mediating postprandial coordination between the antrum and pylorus. Force transducers were implanted on the serosal surface of the body, antrum, pylorus, and duodenum in seven dogs. Dogs were given either a solid or a liquid meal, and gastroduodenal motility was recorded over 10 h. Gastric emptying was evaluated with radiopaque markers mixed with a solid meal. Dogs were treated with hexamethonium, N(G)-nitro-l-arginine methyl ester (l-NAME), or transient vagal nerve blockade by cooling. A postprandial motility pattern showed three distinct phases: early, intermediate, and late. In the late phase, profound pyloric relaxations predominantly synchronized with giant antral contractions that were defined as postprandial antropyloric coordination. A gastric emptying study revealed that the time at which gastric contents entered into the duodenum occurred concomitantly with antropyloric coordination. Treatment by vagal blockade or hexamethonium significantly reduced postprandial antral contractions and pyloric relaxations of the late phase. l-NAME changed pyloric motor patterns from relaxation dominant to contraction dominant. Solid gastric emptying was significantly attenuated by treatment with hexamethonium, l-NAME, and vagal blockade. Postprandial antropyloric coordination was not seen after feeding a liquid meal. It is concluded that postprandial antropyloric coordination plays an important role to regulate gastric emptying of a solid food. Postprandial antropyloric coordination is regulated by the vagus nerve and nitrergic neurons in conscious dogs.

Alpha-helical structure in the C-terminus of vasoactive intestinal peptide: functional and structural consequences

The conformational properties of vasoactive intestinal peptide (VIP) include the N-terminal randomized structure and the C-terminal long alpha-helical structure. We have previously observed that the N-terminal random coil structure plays a crucial role in the receptor-selectivity. Here, to clarify how the formation of the alpha-helix plays a role in its biological functions, we chemically synthesized VIP analogues modified at the C-terminus, mid-chain, and N-terminus of the alpha-helical region, and evaluated the relationship between their alpha-helical contents and their biological activities including relaxant effects on murine stomach and receptor-binding activities. VIP and VIP-(1-27) showed equipotent biological activities with 48% and 50% alpha-helical content, respectively, each of which corresponds to 14 amino acid residues. VIP-(1-26) was 10% and threefold less potent in relaxant and binding activities, respectively, compared with VIP, and its 49% alpha-helical content resulted in 13 residues involved in the alpha-helix. Further truncation from 25 to 21 resulted in decrease in the alpha-helical content from 43% to 29%, corresponding residues from 11 to 6, the relaxant activity from 72% to 4%, and the affinity to the membrane from 60-fold to over 10(4)-fold less potency. In addition, disruption of the mid-chain and the N-terminus in the alpha-helical stretch by oxidation of Met(17) and deletion of Thr(11) also inhibited biological activities. These findings suggest that the presence of alpha-helical structure forming in 14 amino acid residues between position 10 and 23 in VIP is essential to its biological functions and the C-terminal amino acid residues between position 24 and 27 are requisite for this alpha-helical formation.

PAC1 receptor-mediated relaxation of longitudinal muscle of the mouse proximal colon

Since pituitary adenylate cyclase-activating polypeptide (PACAP) was shown to partially mediate nonadrenergic, noncholinergic (NANC) relaxation of longitudinal muscle of the proximal colon of ICR mice, we further studied the receptor subtype activated by PACAP by using a mutant mouse whose PAC1 receptors are markedly reduced. In wild-type mice, the PACAP-mediated component of NANC relaxation was 33%, but it was absent in the mutant mice. The potency of exogenous PACAP in inducing relaxation in the mutant mice was one hundredth of that in wild-type mice. VPAC1 and VPAC2 receptors were not suggested to have any role in the relaxation. These results suggest that PACAP mediates NANC relaxation of longitudinal muscle of mouse proximal colon via PAC1 receptors.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Nitrergic and purinergic regulation of the rat pylorus

The role of nitric oxide (NO) and ATP in the regulation of nonadrenergic, noncholinergic (NANC) inhibitory transmission in the pylorus remains unclear. In the presence of atropine and guanethidine, electric field stimulation induced NANC relaxations in a frequency-dependent manner (1-20 Hz) in the rat pylorus. NANC relaxations were significantly inhibited by N(G)-nitro-L-arginine methyl ester (L-NAME; 10(-4) M). P(2X) purinoceptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; 3 x 10(-5) M) and P(2Y) purinoceptor antagonist reactive blue 2 (2 x 10(-5) M) had no effect on NANC relaxations. However, the combined administration of L-NAME and PPADS, but not reactive blue 2, evoked greater inhibitory effects on NANC relaxation than that evoked by L-NAME alone. alpha-Chymotrypsin and vasoactive intestinal polypeptide antagonist did not affect NANC relaxations. ATP (10(-5)-10(-3) M) and P(2X) purinoceptor agonist alpha, beta-methyleneadenosine 5'-triphosphate (10(-7)-10(-5) M), but not P(2Y) purinoceptor agonist 2-methylthioadenosine 5'-triphosphate (10(-7)-10(-5) M), induced muscle relaxations in a dose-dependent manner, and relaxations were significantly reduced by PPADS and unaffected by TTX. These studies suggest that NO and ATP act in concert to mediate NANC relaxation of the rat pylorus. ATP-induced relaxation appears to be mediated by P(2X) purinoceptors located on smooth muscle cells.

The contractile action of platelet-activating factor on gallbladder smooth muscle

Platelet-activating factor (PAF) may be a mediator of some sequelae of cholecystitis, a disorder with gallbladder motor dysfunction. The aims of this study were to determine the effect and mechanism of PAF on gallbladder muscle. Exogenous administration of PAF-16 or PAF-18 caused dose-dependent contractions of gallbladder muscle strips in vitro with threshold doses of 1 ng/ml and 10 ng/ml, respectively. The PAF-induced contractions were not significantly reduced by TTX, atropine, or hexamethonium but were significantly inhibited with the PAF receptor antagonists ginkolide B and CV-3988. The PAF-induced contraction was reduced by indomethacin. Preventing influx of extracellular calcium with a calcium-free solution nearly abolished the PAF contractile response. Nifedipine inhibited the PAF contractile response, whereas ryanodine had no effect. Pertussis toxin reduced the PAF contractile response. In conclusion, PAF causes gallbladder contraction through specific PAF receptors on gallbladder muscle. These PAF receptors appear to be linked to a prostaglandin-mediated mechanism and to pertussis toxin-sensitive G proteins. The contractile response is largely mediated through the utilization of extracellular calcium influx through voltage-dependent calcium channels.

Electrical and mechanical effects of vasoactive intestinal peptide and pituitary adenylate cyclase-activating peptide in the rat colon involve different mechanisms

This work aimed to study the effects of pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) on the mechanical and electrical activity of the circular muscle of the rat colon and the mechanisms involved in such effects. Spontaneous mechanical activity was studied in vitro in an organ bath and the membrane potential was recorded using the microelectrode technique. Both VIP and PACAP (0.1 microM) caused an immediate, sustained and tetrodotoxin (1 microM)-resistant inhibition of the cyclic spontaneous mechanical activity and hyperpolarization. The small-conductance Ca(2+)-activated K(+) channel blocker, apamin (1 microM), did not change the VIP- and PACAP-induced relaxation but reduced the hyperpolarization induced by PACAP whereas it did not change that induced by VIP. In contrast, the purinoceptor antagonist, suramin (100 microM), blocked the hyperpolarization caused by PACAP and VIP but failed to change their mechanical inhibitory effects. Moreover, the putative PACAP and VIP receptor antagonists, PACAP-(6-38) and VIP-(10-28), respectively, both 3 microM, failed to change the effects of either peptide and modified neither the inhibitory junction potential nor the relaxation induced by electrical-field stimulation. Thus, these results suggest that the mechanisms mediating relaxation are not strictly coupled to the mechanisms mediating hyperpolarization. This could be due to activation of two distinct mechanisms of action after agonist receptor interaction.

Inhibitory neural pathway regulating gastric emptying in rats

The relaxation of the pylorus is one of the most important factors for promoting gastric emptying. However, the role of inhibitory neurotransmitters in the regulation of pyloric relaxation and gastric emptying remains unclear. In this study, we investigated the effects of NO biosynthesis inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), and calcium dependent potassium channel blocker, apamin, on vagal stimulation-induced pyloric relaxation and gastric emptying in rats. Sodium nitroprusside (SNP), adenosine 5'-triphosphate (ATP), vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) caused pyloric relaxations in a dose dependent manner in vivo. Apamin (120 microg/kg) significantly reduced ATP and PACAP-induced pyloric relaxations without affecting SNP- or VIP-induced relaxations. Vagal stimulation (10 V, 1 ms, 1-20 Hz)-induced pyloric relaxation was significantly inhibited by L-NAME (10 mg/kg). The combined administration of L-NAME and apamin almost completely abolished vagal stimulation-induced pyloric relaxation. L-NAME and apamin significantly increased spontaneous contractions in the antrum, pylorus and duodenum. Increased motility index by L-NAME and apamin was significantly higher in the pylorus and duodenum, compared to that of antrum. L-NAME and apamin significantly delayed liquid gastric emptying. These results suggest that besides NO, probably ATP and PACAP, act as inhibitory neurotransmitters in the rat pylorus and regulate gastric emptying.

Biological relevance of pituitary adenylate cyclase-activating polypeptide (PACAP) in the gastrointestinal tract

Since its initial discovery in 1989, pituitary adenylate cyclase activating peptide (PACAP) has been noted to distribute widely in the brain, the respiratory and the gastrointestinal system. It occurs in two bioactive molecules, PACAP-27 and the C-terminally extended PACAP-38, which evoke activity by binding to three distinct types of high-affinity, G-protein coupled membrane receptors. It is present throughout the entirety of the gut but is rare in certain areas such as the intestinal mucosa and islets of Langerhans. PACAP-induced biological effects are protean and include alterations of motility in the bowel and the gallbladder, stimulation of gastric acid and intestinal secretion, hormone/enzyme release from the exocrine and endocrine pancreas, and the induction as well as inhibition of proliferation in neuroendocrine cells and tumors. Its hepatic activity has to date not been elucidated in detail. One of the interesting features of PACAP is the species and organ dependent variation of its biological effects. Of particular note is its superior potency when compared with other neuropeptides identified in the gut, and the involvement of a number of different second messenger systems upon PACAP receptor activation.

Stimulant action of pituitary adenylate cyclase-activating peptide on normal and drug-compromised peristalsis in the guinea-pig intestine

1. Pituitary adenylate cyclase-activating peptide (PACAP) is known to influence the activity of intestinal smooth muscle. This study set out to examine the action of PACAP on normal and drug-inhibited peristalsis and to shed light on its site and mode of action. 2. Peristalsis in isolated segments of the guinea-pig small intestine was elicited by distension through a rise of the intraluminal pressure. Drug-induced motility changes were quantified by alterations of the peristaltic pressure threshold at which aborally moving peristaltic contractions were triggered. 3. PACAP (1-30 nM) stimulated normal peristalsis as deduced from a concentration-related decrease in the peristaltic pressure threshold (maximum decrease by 55%). The peptide's stimulant effect remained intact in segments pre-exposed to apamin (0.5 microM), N-nitro-L-arginine methyl ester (300 microM), naloxone (0.5 microM), atropine (1 microM) plus naloxone (0.5 microM) or hexamethonium (100 microM) plus naloxone (0.5 microM). 4. PACAP (10 nM) restored peristalsis blocked by morphine (10 microM), noradrenaline (1 microM) or N6-cyclopentyladenosine (0.3 microM) and partially reinstated peristalsis blocked by Rp-adenosine-3',5'-cyclic monophosphothioate triethylamine (100 microM) but failed to revive peristalsis blocked by hexamethonium (100 microM) or atropine (1 microM). The peptide's spectrum of properistaltic activity differed from that of naloxone (0.5 microM) and forskolin (0.3 microM). 5. The distension-induced ascending reflex contraction of the circular muscle was facilitated by PACAP (1-30 nM) which itself evoked transient nerve-mediated contractions of intestinal segment preparations. 6. These data show that PACAP stimulates normal peristalsis and counteracts drug-induced peristaltic arrest by a stimulant action on excitatory enteric motor pathways, presumably at the intrinsic sensory neurone level. The action of PACAP seems to involve multiple signalling mechanisms including stimulation of adenylate cyclase.

Control of glucose homeostasis by incretin hormones

In humans as well as in other animal species, the ingestion of food provides the fundamental source of energy for various cellular activities. The intake of food and the ability of controlling the plasma levels of substrates for energy production involve complex mechanisms that ensure a constantly adequate supply of metabolites both in the fasting and in the fed state. A number of hormonal peptides released from the gastrointestinal (GI) tract in response to the ingestion of food have been shown to play a critical role in the postprandial control of glucose homeostasis. They are known to act through three main mechanisms of action. These include; (1) stimulation of insulin secretion of pancreatic islet (beta) cells; (2) inhibition of hepatic gluconeogenesis by suppression of glucagon secretion; and (3) inhibition of GI motility. While for some of these hormones all three mechanisms of action are utilized under physiological conditions, others preferentially use one or a combination of two mechanisms for lowering postprandial hyperglycemia. Although the term glucoincretins (or incretins, or insulinotropic hormones) etymologically only describes factors capable of inducing insulin secretion, it is more frequently used to identify a larger class of peptides that, rather than manifesting a specific mechanism of action (i.e., insulin secretion), share the ability of controlling glucose excursion in the fed state (with or without a direct insulinotropic effect). The latter more inclusive meaning, incretins, is used in this article. This review summarizes recent advances on synthesis, secretion, blood plasma patterns, and metabolism of some of the major GI regulatory peptides acting in the postprandial state.