Pancreatic polypeptide stimulates gastric motility through a vagal-dependent mechanism in rats

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

Peptide hormones and lipopeptides: from self-assembly to therapeutic applications

This review describes the properties and activities of lipopeptides and peptide hormones and how the lipidation of peptide hormones could potentially produce therapeutic agents combating some of the most prevalent diseases and conditions. The self‐assembly of these types of molecules is outlined, and how this can impact on bioactivity. Peptide hormones specific to the uptake of food and produced in the gastrointestinal tract are discussed in detail. The advantages of lipidated peptide hormones over natural peptide hormones are summarised, in terms of stability and renal clearance, with potential application as therapeutic agents. © 2017 The Authors Journal of Peptide Science published by European Peptide Society and John Wiley & Sons Ltd.

Pancreatic polypeptide stimulates mouse gastric motor activity through peripheral neural mechanisms

BACKGROUND

Pancreatic polypeptide (PP) is supposed to be one of the major endogenous agonists of the neuropeptide Y4 receptor. Pancreatic polypeptide can influence gastrointestinal motility, acting mainly through vagal mechanisms, but whether PP acts directly on the stomach has not been explored yet. The aims of this study were to investigate the effects of PP on mouse gastric emptying, on spontaneous tone of whole stomach in vitro and to examine the mechanism of action.

METHODS

Gastric emptying was measured by red phenol method after i.p. PP administration (1-3 nmol per mouse). Responses induced by PP (1-300 mmol L^-1 ) on gastric endoluminal pressure were analyzed in vitro in the presence of different drugs. Gastric genic expression of Y4 receptor was verified by RT-PCR.

KEY RESULTS

Pancreatic polypeptide dose-dependently increased non-nutrient liquid gastric emptying rate. In vitro, PP produced a concentration-dependent contraction that was abolished by tetrodotoxin, a neural blocker of Na⁺ voltage-dependent channels. The contractile response was significantly reduced by atropine, a muscarinic receptor antagonist, and by SR48968, an NK2 receptor antagonist, while it was potentiated by neostigmine, an inhibitor of acetylcholinesterase. The joint application of atropine and SR48968 fully abolished PP contractile effect. Reverse transcriptase-polymerase chain reaction analysis revealed the presence of Y4 receptor mRNA in mouse stomach with a greater expression in antrum than in fundus.

CONCLUSIONS & INFERENCES

The present findings demonstrate that exogenous PP stimulates mouse gastric motor activity, by acting directly on the stomach. This effect appears due to the activation of enteric excitatory neurons releasing acetylcholine and tachykinins.

The role of alginates in regulation of food intake and glycemia: a gastroenterological perspective

Regulation of food intake through modulation of gastrointestinal responses to ingested foods is an ever-growing component of the therapeutic approaches targeting the obesity epidemic. Alginates, viscous and gel-forming soluble fibers isolated from the cell wall of brown seaweeds and some bacteria, are recently receiving considerable attention because of their potential role in satiation, satiety, and food intake regulation in the short term. Enhancement of gastric distension, delay of gastric emptying, and attenuation of postprandial glucose responses may constitute the basis of their physiological benefits. Offering physical, chemical, sensorial, and physiological advantages over other viscous and gel-forming fibers, alginates constitute promising functional food ingredients for the food industry. Therefore, the current review explores the role of alginates in food intake and glycemic regulation, their underlying modes of action and their potential in food applications.

[Prevention of gastrostasis after pancreaticoduodenal resection: new technique of gastroenterostomy]

It was performed a retrospective comparative analysis of treatment results of 113 patients with pancreatic head and periampular cancer. The main group consisted of 58 patients in whom pancreaticoduodenal resection was performed according to an original technique of Russian Scientific Center of Surgery. Control group included 55 patients who underwent end-to-side gastrojejunostomy reconstruction. We have analyzed immediate postoperative complications in 2 groups without taking into consideration nosological forms of the disease. Pancreaticojejunostomy failure was diagnosed postoperatively in 5 (8.6%) patients in main group and in 10 (18.2%) patients in control group. There was no hepaticoentero- and gastroenterostomy failure in patients who underwent new technique of gastrojejunostomy while these events were observed in 8 (14.5%) and 3 (5.5%) patients respectively in control group. Mortality was 1.7% (n=1) in main group and 5.5% (n=3) in control group (p=0.29). Mild degree of gastrostasis (A class) was observed in 54 (93.7%) patients of main group and in 34 (61.8%) patients of control group (p=0.0004). There was B class of gastrostasis in 4 (6.9%) patients of main group. Severe gastrostasis (C class) was not revealed in any observation. In control group B class of gastrostasis was diagnosed in 14 (25.5%) patients, severe degree - in 7 (12.7%) patients. Univariant analysis showed hemotransfusion (p=0.037), pancreatic fistula (p=0.001), enteric fistula (p=0.005) and reconstruction technique (p=0.00004) as predictors of gastrostasis. Multivariant analysis defined pancreatic fistula (p=0.01), enteric fistula (p=0.04) and reconstruction technique (p=0.001) as significant predictors of gastrostasis. Thus, our study revealed significant decreasing gastrostasis incidence in case of original technique in comparison with conventional anastomosis, as well as demonstrated effect of anastomoses failure on augmentation of gastrostasis frequency after pancreaticoduodenal resection. Further randomized investigations are necessary to confirm our results.

Effect of pancreatic polypeptide on gastric accommodation and gastric emptying in conscious rats

Pancreatic polypeptide (PP) is an anorexigenic hormone released from pancreatic F cells upon food intake. We aimed to determine the effect of PP on gastric accommodation and gastric emptying in conscious Wistar HAN rats to investigate whether effects on motor function could contribute to its anorexigenic effects. Intragastric pressure (IGP) was measured through a chronically implanted gastric fistula during the infusion of a nutrient meal (Nutridrink; 0.5 ml/min). Rats were treated with PP (0, 33 and 100 pmol·kg(-1)·min(-1)) in combination with N(G)-nitro-L-arginine methyl ester (L-NAME; 180 mg·kg(-1)·h(-1)), atropine (3 mg·kg(-1)·h(-1)), or vehicle. Furthermore, the effect of PP was tested after subdiaphragmal vagotomy of the stomach. Gastric emptying of a noncaloric and a caloric meal after treatment with 100 pmol·kg(-1)·min(-1) PP or vehicle was compared using X-rays. PP significantly increased IGP during nutrient infusion compared with vehicle (P < 0.01). L-NAME and atropine significantly increased IGP during nutrient infusion compared with vehicle treatment (P < 0.005 and 0.01, respectively). The effect of PP on IGP during nutrient infusion was abolished in the presence of L-NAME and in the presence of atropine. In vagotomized rats, PP increased IGP compared with intact controls (P < 0.05). PP significantly delayed gastric emptying of both a noncaloric (P < 0.05) and a caloric (P < 0.005) meal. PP inhibits gastric accommodation and delays gastric emptying, probably through inhibition of nitric oxide release. These results indicate that, besides the well-known centrally mediated effects, PP might decrease food intake through peripheral mechanisms.

Quantification of the effects of the volume and viscosity of gastric contents on antral and fundic activity in the rat stomach maintained ex vivo

AIMS

The aim of this study was to examine the effect of varying the rheological properties of perfusate on the volume and muscular activity of the various compartments of the rat stomach.

METHODS

Image analysis was used to quantify the activity of the ex vivo stomach preparations when perfused according to a ramp profile.

RESULTS

The area of the fundus increased to a greater extent than that of the body when watery or viscous material was perfused. However, initial distension of the corpus was greater and occurred more rapidly when viscous material was perfused. Only the fundus expanded when perfusion followed the administration of verapamil. The frequency of antrocorporal contractions decreased significantly and the amplitude of antrocorporal contractions increased significantly with increase in gastric volume. The velocity of antrocorporal contractions did not vary with gastric volume but varied regionally in some preparations being faster distally than proximally. Neither the frequency, amplitude or velocity of antrocorporal contractions differed when pseudoplastic rather than watery fluid was perfused. However, the characteristics of antrocorporal contractions changed significantly when the stomach was perfused with material with rheological characteristics that induce different patterns of wall tension to those normally encountered. Hence, the mean frequency and speed of propagation of antrocorporal contractions increased and their direction of propagation became inconstant.

Bowels control brain: gut hormones and obesity

Food intake and energy expenditure are tightly regulated by the brain, in a homeostatic process that integrates diverse hormonal, neuronal and metabolic signals. The gastrointestinal tract is an important source of such signals, which include several hormones released by specialized enteroendocrine cells. These hormones exert powerful effects on appetite and energy expenditure. This Review addresses the physiological roles of peptide YY, pancreatic polypeptide, islet amyloid polypeptide, glucagon-like peptide 1, glucagon, oxyntomodulin, cholecystokinin and ghrelin and discusses their potential as targets for the development of novel treatments for obesity.

Different regulation of atrial ANP release through neuropeptide Y2 and Y4 receptors

Neuropeptide Y (NPY) receptors are present in cardiac membranes. However, its physiological roles in the heart are not clear. The aim of this study was to define the direct effects of pancreatic polypeptide (PP) on atrial dynamics and atrial natriuretic peptide (ANP) release in perfused beating atria. Pancreatic polypeptides, a NPY Y(4) receptor agonist, decreased atrial contractility but was not dose-dependent. The ANP release was stimulated by PP in a dose-dependent manner. GR 23118, a NPY Y(4) receptor agonist, also increased the ANP release and the potency was greater than PP. In contrast, peptide YY (3-36) (PYY), an NPY Y(2) receptor agonist, suppressed the release of ANP with positive inotropy. NPY, an agonist for Y(1, 2, 5) receptor, did not cause any significant changes. The pretreatment of NPY (18-36), an antagonist for NPY Y(3) receptor, markedly attenuated the stimulation of ANP release by PP but did not affect the suppression of ANP release by PYY. BIIE0246, an antagonist for NPY Y(2) receptor, attenuated the suppression of ANP release by PYY. The responsiveness of atrial contractility to PP or PYY was not affected by either of the antagonists. These results suggest that NPY Y(4) and Y(2) receptor differently regulate the release of atrial ANP.

Y2, Y4 receptors and obesity

The neuropeptide Y system - comprising neuropeptide Y, peptide YY, pancreatic polypeptide and the Y receptors through which they act (Y1, Y2, Y4, Y5 and y6) - has been at the center of attention with regards to regulation of feeding behavior and its possible involvement in obesity. In the past, research has focused mainly on the orexigenic and obesogenic action of this system, with Y1 and Y5 receptors being prime candidates as mediators of neuropeptide Y-induced hyperphagia and obesity. However, in recent years, the role of other members of the neuropeptide Y family, peptide YY, pancreatic polypeptide and the Y2 and Y4 receptors through which they predominantly act, have commanded increasing attention on account of their effects to mediate satiety and promote weight loss via actions in key brain structures, such as the arcuate nucleus of the hypothalamus and the brain stem. This review focuses on the role of peptide YY- and pancreatic polypeptide-like compounds as possible antiobesity drugs, taking into account their effects, not only on energy balance, but also in the regulation of bone formation, and highlights potential benefits of using Y2 and/or Y4 antagonists (as opposed to agonists such as peptide YY or pancreatic polypeptide) in the treatment of obesity.

Delayed gastric emptying is associated with pylorus-preserving but not classical Whipple pancreaticoduodenectomy: A review of the literature and critical reappraisal of the implicated pathomechanism

Pylorus-preserving pancreaticoduodenectomy (PPPD) is nowadays considered the treatment of choice for periampullary tumors, namely carcinoma of the head, neck, or uncinate process of the pancreas, the ampulla of Vater, distal common bile duct or carcinoma of the peri-Vaterian duodenum. Delayed gastric emptying (DGE) comprises one of the most troublesome complications of this procedure. A search of the literature using Pubmed/Medline was performed to identify clinical trials examining the incidence rate of DGE following standard Whipple pancreaticoduodenectomy (PD) vs PPPD. Additionally we performed a thorough in-depth analysis of the implicated pathomechanism underlying the occurrence of DGE after PPPD. In contrast to early studies, the majority of recently performed clinical trials demonstrated no significant association between the occurrence of DGE with either PD or PPPD. PD and PPPD procedures are equally effective operations regarding the postoperative occurrence of DGE. Further randomized trials are required to investigate the efficacy of a recently reported (but not yet tested in large-scale studies) modification, that is, PPPD with antecolic duodenojejunostomy.

Gut peptides and the regulation of appetite

There is a growing worldwide epidemic of obesity. Obese people have a higher incidence of type 2 diabetes and cardiovascular disease, and hence present increasing social, financial and health burdens. Weight loss is always difficult to achieve through lifestyle changes alone, and currently licensed anti-obesity drug treatments, such as orlistat and sibutramine, if tolerated, only achieve modest weight loss. Therefore, there is a need to identify more potent pharmacological targets. In the last 10 years, discoveries of new hormones such as leptin and ghrelin, together with greater understanding of previously described hormones such as cholecystokinin (CCK), pancreatic polypeptide (PP), peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), have led to a rapid increase in our knowledge of the regulation of energy balance. Among the most important factors, controlling appetite and satiety are peptide hormones released from the gut. In this paper, we provide a full up-to-date overview of the current state of knowledge of this field, together with the potential of these peptides as drugs, or as other therapeutic targets, in the treatment of obesity. Finally, we propose an integrated model to describe the complex interplay of these hormones in the broader physiology of energy balance.

Effects of pancreatic polypeptide on pancreas-projecting rat dorsal motor nucleus of the vagus neurons

We investigated the pre- and postsynaptic effects of pancreatic polypeptide (PP) on identified pancreas-projecting neurons of the rat dorsal motor nucleus of the vagus in thin brain stem slices. Perfusion with PP induced a TTX- and apamin-sensitive, concentration-dependent outward (22% of neurons) or inward current (21% of neurons) that was accompanied by a decrease in input resistance; PP was also found to affect the amplitude of the action potential afterhyperpolarization. The remaining 57% of neurons were unaffected. PP induced a concentration-dependent inhibition in amplitude of excitatory (n = 22 of 30 neurons) and inhibitory (n = 13 of 17 neurons) postsynaptic currents evoked by electrical stimulation of the adjacent nucleus of the solitary tract, with an estimated EC(50) of 30 nM for both. The inhibition was accompanied by an alteration in the paired pulse ratio, suggesting a presynaptic site of action. PP also decreased the frequency, but not amplitude, of spontaneous excitatory (n = 6 of 11 neurons) and inhibitory currents (n = 7 of 9 neurons). In five neurons, chemical stimulation of the area postrema (AP) induced a TTX-sensitive inward (n = 3) or biphasic (outward and inward) current (n = 2). Superfusion with PP reversibly reduced the amplitude of these chemically stimulated currents. Regardless of the PP-induced effect, the vast majority of responsive neurons had a multipolar somata morphology with dendrites projecting to areas other than the fourth ventricle or the central canal. These results suggest that pancreas-projecting rat dorsal motor nucleus of the vagus neurons are heterogeneous with respect to their response to PP, which may underlie functional differences in the vagal modulation of pancreatic functions.

Gastric electrical stimulation is associated with improvement in pancreatic exocrine function in humans

OBJECTIVE

To define the possible effects of gastric electrical stimulation (GES) for gastroparesis on pancreatic function, we performed 2 related human studies.

METHODS

Fecal elastase values were compared in 2 patient groups: (1) GES devices ON and (2) GES devices OFF and (2) in 3 control groups: (1) no response (NR) to prokinetic medications, (2) positive response (RES) to medications, and (3) normal controls. Polypeptide levels in 7 of 9 GES patients with device ON and OFF, elastase results, GI symptoms (TSS), and heart rate variability (HRV) were compared by paired t tests and/or ANOVA and reported as mean +/- SE.

RESULTS

Elastase was different for GES-ON and OFF (508.0 +/- 92.2 vs. GES-OFF 378.6 +/- 87.4, P < 0.05). Elastase was lower in medication NR and RES than in normal controls. Postprandial pancreatic polypeptide was greater with GES ON than OFF (P = 0.07). HRV revealed a lower percentage of change with device ON versus OFF (44.2 +/- 5.5 vs. 48.5 +/- 5.2, P = 0.08) and lower TSS with ON versus OFF (15.9 +/- 4.5 vs. 25.7 +/- 5.3, P < 0.05).

CONCLUSIONS

GES improves exocrine pancreatic release, effects autonomic control, and improves GI symptoms, suggesting a possible role for GES in the treatment of pancreatic insufficiency associated with gastroparesis.

Impairment of gastrointestinal motility by nitrate administration: evaluation based on electrogastrographic changes and autonomic nerve activity

BACKGROUND

Nitrates decrease the tone of the lower oesophageal sphincter, and may thus induce gastro-oesophageal reflux.

AIM

In the present study, we evaluated electrogastrographic changes and heart-rate variability before and after the administration of nitrates.

METHODS

In 15 patients with chest pain treated with nitrates, electrocardiography and percutaneous electrogastrography were performed before and after administration of nitrates. Autonomic nervous system function was evaluated by spectral analysis of heart-rate variability and serial changes in low frequency and high frequency power, and the low frequency/high frequency ratio were compared. Electrogastrograms were analysed by obtaining peak power amplitudes and their dominant frequencies.

RESULTS

After the administration of nitrates (isosorbide dinitrate), high frequency power, an index of parasympathetic nervous activity, was significantly decreased, whereas the low frequency/high frequency ratio, an index of sympathetic nervous activity, was significantly increased. The mean peak amplitude of the electrogastrogram significantly increased postprandially both before and after treatment. After isosorbide dinitrate treatment, however, mean peak amplitudes after a meal were significantly lower than those obtained before treatment. The mean dominant frequency of the electrogastrogram did not vary before and after treatment.

CONCLUSIONS

The present study suggests that nitrates inhibit gastrointestinal motility by decreasing autonomic nervous activity.

Video-based spatio-temporal maps for analysis of gastric motility in vitro: effects of vagal stimulation in guinea-pigs

Our aim was to evaluate topographically specific gastric motility changes induced by graded vagal activation. A recently developed method of constructing spatio-temporal maps of motility from video movies was adapted to the in vitro perfused guinea-pig stomach with an intact vagal nerve supply. In the unstimulated preparation, spontaneous activity was low or absent. Bilateral vagal stimulation with frequencies as low as 0.2 Hz triggered weak anally, and in some cases orally, propagating antral contractions at rates of about 5-6 min-1. Upon stimulation with higher frequencies, antral contractions increased significantly in length (starting more proximally) and amplitude, and produced large pressure peaks of up to 25 hPa, with maximal effects at 2-4 Hz. In contrast, the speed of propagation and the interval between peristaltic waves did not change with vagal stimulation at any frequency. Vagal stimulation also produced a significant and frequency-dependent enlargement of the fundus with a maximal effect at 4 Hz. It is concluded that a very low tonic vagal activity is apparently necessary and sufficient to express basic antral motility, while more sustained vagal activity is necessary for high-amplitude gastric contractions and significant sustained fundic relaxation. The constant interval between propagating contractions supports the concept that vagal input impinges on intrinsic enteric neural circuits that have a modulatory role in the myogenic mechanism underlying slow-wave peristalsis, rather than directly on gastric musculature.

Roles of pancreatic polypeptide in regulation of food intake

Pancreatic polypeptide (PP) is produced in pancreatic islets of Langerhans and released into the circulation after ingestion of a meal. Peripherally administered PP suppresses food intake and gastric emptying. On the other hand, central administration of PP elicits food intake and gastric emptying. Therefore, PP actions on food intake may be, in part, attributable to gastric emptying. PP transgenic mice exhibit decreases in both food intake and gastric emptying rate that were clearly reversed by anti-PP antiserum. PP is an anorexigenic signal in the periphery and an orexigenic signal in the central nervous system.

Peptidergic regulation of gastrointestinal motility in rodents

Peptides involved in the endocrine and enteric nervous systems as well as in the central nervous system exert concerted action on gastrointestinal motility. Mechanical and chemical stimuli which induce peptide release from the epithelial endocrine cells are the earliest step in the initiation of peristaltic activities. Gut peptides exert hormonal effects, but peptide-containing stimulatory (Ach/substance P/tachykinin) and inhibitory (VIP/PACAP/NO) neurons are also involved in the induction of ascending contraction and descending relaxation, respectively. The dorsal vagal complex (DVC), located in the medulla of the brainstem, constitutes the basic neural circuitry of vago-vagal reflex control of gastrointestinal motility. Several gut peptides act on the DVC to modify vagal cholinergic reflexes directly (PYY and PP) or indirectly via afferent fibers in the periphery (CCK and GLP-1). The DVC is also a primary site of action of many neuropeptides (such as TRH and NPY) in mediating gastrointestinal motor activities. The identification over the last few years of a number of neuropeptide systems has greatly changed the field of feeding and body weight regulation. By exploring the brain and gut systems that employ recently identified peptidergic molecules, it will be possible to elaborate on the central and peripheral pathways involved in the regulation of gastrointestinal motility.

Decreased food intake and body weight in pancreatic polypeptide-overexpressing mice

BACKGROUND & AIMS

Pancreatic polypeptide (PP) is a 36-amino acid hormone produced by F cells within the pancreatic islets and the exocrine pancreas. The definitive function of PP in mammalian physiology remains to be determined. This study examined the effects of chronic overexpression of PP through the development of PP transgenic mice.

METHODS

PP transgenic mice were created by using mouse PP complementary DNA under the control of the cytomegalovirus immediate early enhancer-chicken beta-actin hybrid promoter (pCAGGS expression vector).

RESULTS

A unique line of transgenic mice was created that overexpresses PP in the pancreatic islets with low levels of expression in other tissues including the brain. Plasma PP concentrations were more than 20 times higher than those of control littermates. However, PP overproduction led to postnatal lethality in half of the pups because of markedly decreased milk intake. The remaining PP transgenic mice gained less weight with specifically reduced food intake and fat mass compared with controls, a result that was more evident in male than in female mice. The transgenic mice exhibited a reduced rate of gastric emptying of a solid meal but had normal oxygen consumption and fasting leptin levels. Immunoneutralization with anti-PP antiserum reversed the phenotypic changes of transgenic animals.

CONCLUSIONS

PP could be involved in feeding and body weight regulation partly through regulation of gastric emptying.

The endocrine pancreas in virgin and pregnant offspring of diabetic pregnant rats

Diabetes of the mother during pregnancy induces structural and functional adaptations in the fetal endocrine pancreas. We have previously shown in our experimental rat model, that the impact of this abnormal intra-uterine milieu leads, in the adult offspring, to a disturbance of the glucose homeostasis and to the development of gestational diabetes. The aim of the present work is to investigate wether these functional differences can be explained by structural differences at the level of the endocrine pancreas. Therefore the size and the structure of the endocrine pancreas, as well as the contribution of the insulin-, glucagon-, somatostatin- and PP-cells, were investigated morphometrically in the adult youngsters of mildly and of severely diabetic mothers, since both display a disturbed glucose tolerance but with divergent characteristics. Also the adaptation of their endocrine pancreas to pregnancy was measured and compared to that of a control pregnancy. In the offspring of mildly diabetic mothers, the size of the endocrine pancreas and the distribution of the islets of Langerhans are normal. Also the doubling of the endocrine mass during pregnancy is similar to controls. The high proportion of A-cells, especially in relation to a normal B-cell mass and the low amount of PP-cells, might play a role in the impairment of the insulin response in these animals and in the development of gestational diabetes. In the offspring of severely diabetic mothers a clear hypertrophy of the endocrine pancreas is noted, which is mainly due to the presence of numerous small islets and which does not increase further during pregnancy. In these animals, the size of the endocrine pancreas and of the B-cell mass have reached 'pregnant' values without pregnancy, which coincides with an exaggerated insulin output and peripheral insulin resistance, as during normal pregnancy. No further increase in islet mass is seen during pregnancy, which is associated with gestational diabetes.

Gastric emptying following pylorus-preserving Whipple and duodenum-preserving pancreatic head resection in patients with chronic pancreatitis

BACKGROUND

After pylorus-preserving Whipple (PPW), delayed gastric emptying (DGE) is reported in up to 50% of these patients. We analyzed gastric emptying and hormonal adaptation of cholecystokinin (CCK), pancreatic polypeptide (PP), and gastrin following two surgical procedures for chronic pancreatitis (CP): the PPW and the duodenum-preserving pancreatic head resection (DPPHR).

METHODS

Ten patients underwent DPPHR and 10 underwent PPW for CP. Preoperatively and 10 days and 6 months postoperatively, gastric emptying (paracetamol absorption test) and CCK, gastrin, and PP were measured using a test meal stimulation.

RESULTS

The area under the serum paracetamol time curve for 0 to 120 minutes (AUC) showed no preoperative difference. Ten days postoperatively, the AUC was significantly reduced (P <0.05) after PPW but not after DPPHR. Six months postoperatively, AUC was comparable with the preoperative findings in DPPHR and PPW. The integrated 180-minute PP release was significantly reduced 10 days and 6 months postoperatively in both groups. The integrated 180-minute CCK release was decreased 10 days after PPW, but failed to be significant (P = 0.053). Gastrin levels were postoperatively unchanged.

CONCLUSION

Following DPPHR we found no delay in gastric emptying. In contrast, DGE occurs early after PPW. Our data may help explain the slower recovery in PPW patients with regard to weight gain and relief from pain, which may be due to the functional alteration of gastric emptying and motility after this type of surgery.

Physiologic responses to sensory stimulation by food: nutritional implications

The importance of sensory factors (both the sensory properties of foods and sensory abilities of consumers) in food selection is widely accepted. Less recognized and understood are the effects of sensory stimulation on physiologic processes. Mere exposure to the sight, smell, taste, and textural attributes of foods elicits myriad digestive, endocrinologic, thermogenic. cardiovascular, and renal responses. The responses are rapid (generally occurring within minutes of sensory stimulation), small (relative to the magnitude achieved when food is actually being metabolized), and transient (returning to near-baseline levels within minutes). Nevertheless, they have been hypothesized to prime the body to better absorb and use ingested nutrients. They are termed preabsorptive or cephalic phase responses. This review summarizes current knowledge of stimuli that trigger cephalic phase responses and selected response features (eg, magnitude and type of enzymes or hormones released). Mechanisms by which cephalic phase responses may influence nutrient absorption and use are proposed. Current knowledge of the behavioral and physiologic importance of cephalic phase responses is limited, thereby hampering development of dietary recommendations for preventive or therapeutic interventions. Further study of several identified promising areas of application and other easily proposed situations may provide a basis for expanded medical nutrition therapy.

Effect of pancreatic polypeptide on rat dorsal vagal complex neurons

1. Pancreatic polypeptide (PP) microinjected into the dorsal vagal complex (DVC) elevates gastric activity through a vagal mechanism. Thus, it was hypothesized that PP alters the activity of nuclei comprising the DVC, i.e. the nucleus tractus solitarii (NTS) and the dorsal motor nucleus (DMN). 2. In vivo and in vitro approaches were used. For in vivo studies, micropipettes were used for recording and injecting vehicle or PP. Neurons were identified as NTS or DMN using orthodromic and antidromic activation, respectively, following vagal stimulation. Gastric-related DVC neurons were located using antral inflation. For in vitro studies, DMN neurons were recorded from medullary slices. 3. Of the twenty-eight NTS and DMN neurons identified, fifteen were activated, six inhibited and seven unaffected after PP microinjection. Forty-two gastric-related neurons were located in the DVC, of which twenty-five were stimulated by PP and seventeen exhibited no change. No gastric-related cells were inhibited. 4. For in vitro studies, 66% of DMN neurons were activated by PP (n = 27/47) while the remaining 33% were inhibited (n = 14/47). Similar results were obtained in normal or synaptic blockade media. 5. These results support the hypothesis that PP alters DVC neuronal activity, which may thereby lead to the previously observed alterations in gastric activity.

Vagal control of digestion: modulation by central neural and peripheral endocrine factors

Vago-vagal reflex control circuits in the dorsal vagal complex of the brainstem provide overall coordination over digestive functions of the stomach, small intestine and pancreas. The neural components forming these reflex circuits are under significant descending neural control. By adjusting the excitability of the different components of the reflex, alterations in digestion control can be produced by the central nervous system. Additionally, the dorsal vagal complex is situated within a circumventricular region without an effective "blood-brain barrier". As a result, vago-vagal reflex circuitry is also exposed to humoral influences which profoundly alter digestive functions by acting directly on brainstem neurons. Behavioral and endocrine physiological observations suggest that this "humoral afferent pathway" may significantly alter the regulation of food intake.