Vagotomy and antrectomy impairs canine fat absorption from solid but not liquid dietary sources

Localization and neurochemical characteristics of the extrinsic sympathetic neurons projecting to the pylorus in the domestic pig

The pylorus, an important part of the digestive tract controlling the flow of chyme between the stomach and the duodenum, is widely innervated by intrinsic and extrinsic nerves. To determine the locations of postganglionic sympathetic perikarya that innervate the pylorus of the domestic pig, a retrograde tracing method with application of Fast Blue tracer was used. All positive neuronal cell bodies (ca. 1750) were found in the celiac-cranial mesenteric ganglion complex (CSMG), however, the coeliac poles of this complex provided the major input to the pylorus. Afterwards, the immunohistochemical staining procedure was applied to determine biologically active substances expressed in the FB-labeled perikarya. Approximately 77% of the FB-positive cell bodies contained tyrosine hydroxylase (TH), 87% dopamine β-hydroxylase (DβH), 40% neuropeptide Y (NPY), 12% somatostatin (SOM) and 7% galanin (GAL). The presence of all these substances in the ganglion tissue was confirmed by RT-PCR technique. Double immunocytochemistry revealed that all of the TH-positive perikarya contained DβH, about 40% NPY, 12% SOM and 8% GAL. Additionally, all above-cited immunohistochemical markers as well as VIP, PACAP, ChAT, LEU, MET, SP and nNOS were observed within nerve fibers associated with the FB-positive perikarya. Immunocytochemical labeling of the pyloric wall tissue disclosed that TH+, DβH+ and NPY+ nerve fibers innervated ganglia of the myenteric and submucosal plexuses, blood vessels, both muscular layers and the muscularis mucosae; nerve fibers immunoreactive to GAL mostly innervated both muscular layers, while SOM+ nerve fibers were observed within the myenteric plexus. Presented study revealed sources of origin and immunohistochemical characteristics of the sympathetic postganglionic perikarya innervating the porcine pylorus.

Neural regulation of intestinal nutrient absorption

The nervous system and the gastrointestinal (GI) tract share several common features including reciprocal interconnections and several neurotransmitters and peptides known as gut peptides, neuropeptides or hormones. The processes of digestion, secretion of digestive enzymes and then absorption are regulated by the neuro-endocrine system. Luminal glucose enhances its own absorption through a neuronal reflex that involves capsaicin sensitive primary afferent (CSPA) fibres. Absorbed glucose stimulates insulin release that activates hepatoenteric neural pathways leading to an increase in the expression of glucose transporters. Adrenergic innervation increases glucose absorption through α1 and β receptors and decreases absorption through activation of α2 receptors. The vagus nerve plays an important role in the regulation of diurnal variation in transporter expression and in anticipation to food intake. Vagal CSPAs exert tonic inhibitory effects on amino acid absorption. It also plays an important role in the mediation of the inhibitory effect of intestinal amino acids on their own absorption at the level of proximal or distal segment. However, chronic extrinsic denervation leads to a decrease in intestinal amino acid absorption. Conversely, adrenergic agonists as well as activation of CSPA fibres enhance peptides uptake through the peptide transporter PEPT1. Finally, intestinal innervation plays a minimal role in the absorption of fat digestion products. Intestinal absorption of nutrients is a basic vital mechanism that depends essentially on the function of intestinal mucosa. However, intrinsic and extrinsic neural mechanisms that rely on several redundant loops are involved in immediate and long-term control of the outcome of intestinal function.

The pylorus

The pylorus controls the flow between a reservoir dedicated to mechanical and chemical digestion (the stomach) and a conduit dedicated to the absorption of nutrients (the intestines). The pylorus adjusts gastric outflow resistance to physiological needs. It allows the outflow of isotonic fluids yet selectively retains particles too large for delivery to the intestines and in concert with the antrum further processes them (gastric sieving). Unlike most gut sphincters, the pylorus, at least of man, maintains a patent lumen most of the time. It only intermittently becomes a tightly closed barrier that arrests all flow out of and into the stomach. The geometry of the pylorus changes dramatically from the relaxed open state to closure. Pyloric closure involves contraction of its proximal and distal muscle loops, and occlusion of its lumen by mucosal folds. Current studies that combine pressure recordings with imaging by magnetic resonance imaging or ultrasound and fluid-mechanical analysis shed new light on the role of the pylorus in gastric emptying and digestion. Much has been learned in recent years on the innervation of the normal pylorus particularly from studies on infantile hypertrophic stenosis, and attempts are being made to treat gastroparesis by interventions on the pylorus.

Pylorus-preserving pancreaticoduodenectomy in the treatment of chronic pancreatitis

The pylorus-preserving pancreaticoduodenectomy (PPPD) is an alternative to the standard Whipple resection in the treatment of chronic pancreatitis. The operation is safe and can be performed with a low mortality rate. The most common early complication is delayed gastric emptying, which occurs in 25% to 30% of patients, and generally results in longer hospital stays than the standard Whipple procedure. Follow-up studies show that both operations are equally effective in relieving pain in approximately 75% of selected patients. In the long term, the PPPD successfully preserves physiologic gastric emptying, but at the cost of a higher marginal ulceration rate. The purported nutritional advantages of the PPPD over the classic Whipple resection have not been clearly established. At present, the PPPD is the procedure of choice for patients with chronic pancreatitis requiring panceraticoduodenectomy. Based on available information, this recommendation appears to arise form the fact that the PPPD is less radical than the regular Whipple procedure, and some surgeons find it technically easier. Our experience fails to show a distinct superiority of the PPPD over the Whipple operation.

Stimulation of jejunal synthesis of apolipoprotein A-IV by ileal lipid infusion is blocked by vagotomy

We examined the role of vagal innervation in lipid-stimulated increases in expression and synthesis of intestinal apolipoprotein A-IV (apoA-IV). In rats with duodenal cannulas and superior mesenteric lymph fistulas given duodenal infusions of lipid emulsion, vagotomy had no effect on either intestinal lipid transport, lymphatic apoA-IV output, or jejunal mucosal apoA-IV synthesis. In rats with jejunal Thiry-Vella fistulas, ileal lipid infusion elicited a twofold stimulation of apoA-IV synthesis without affecting apoA-IV mRNA levels; vagotomy blocked this increase in apoA-IV synthesis. Direct perfusion of jejunal Thiry-Vella fistulas produced 2- to 2.5-fold increases in both apoA-IV synthesis and mRNA levels in the Thiry-Vella segment; these effects were not influenced by vagal denervation. These results suggest two mechanisms whereby lipid stimulates intestinal apoA-IV production: 1) a vagal-dependent stimulation of jejunal apoA-IV synthesis by distal gut lipid that is independent of changes in apoA-IV mRNA levels and 2) a direct stimulatory effect of proximal gut lipid on both synthesis and mRNA levels of jejunal apoA-IV that is independent of vagal innervation.

Long-term results of octreotide-therapy in severe dumping syndrome

OBJECTIVE

Little is known about the long-term results of octreotide therapy in dumping syndrome. We report the results of an open study including 20 patients with severe dumping symptoms after gastric surgery treated with octreotide between 1987 and 1997 at the Leiden University Medical Centre.

DESIGN

Patient selection was based on (1) the results of a dumping provocation test and (2) symptoms that were refractory to other therapeutic measures. At regular intervals the presence of dumping symptoms was evaluated together with measurement of body weight and faecal fat excretion.

RESULTS

Mean follow-up was 37 +/- 9 months (range 1-107 months). Doses of octreotide ranged from 25 to 200 microg/day. Initial relief of symptoms was achieved in all subjects, but after three months of therapy symptom relief persisted in 80% of patients. Mean body weight increased by 2.4 +/- 1.2 kg despite a significant increase in faecal fat excretion from 10 +/- 2 g/24 h to 24 +/- 3 g/24 h. Reasons for discontinuation of therapy were diminished efficacy in the longer term in 4 patients and side-effects in 7 patients. Biliary complications were encountered in 3 patients.

CONCLUSIONS

Self-administration of octreotide proves an effective symptomatic treatment of severe dumping, even on the long-term. Its use is frequently limited by the occurrence of side-effects.

Malabsorption associated with surgical procedures and its treatment

Signs and symptoms of malabsorption after surgical procedures can be subtle and recognized late. This article reviews some of the more common surgical procedures potentially associated with malabsorption and suggests techniques of nutrition intervention. Early recognition, and preferably preventative care, should result in improved patient outcome.

Disproportionate ileal digestion on canine food consumption. A possible model for satiety in pancreatic insufficiency

In animals, ileal sensors of nutrients signal satiety more potently than similar sensors in jejunum. We postulated that inadequate food intake and weight loss in human pancreatic insufficiency might arise by the displacement of digestion to ileum, where excessive release of digestive products would enhance satiety. To test this idea, we studied dogs prepared with pancreatic fistulas, which allowed reversible switching of pancreatic juice from entry at duodenum to entry at mid-small intestine. Dogs were studied in a crossover design over successive eight-day periods. Food consumption and body weight were measured while the dogs had continuous access to food. Diversion of pancreatic juice to mid-intestine significantly (P < 0.01) depressed food intake by an average of 28%. Diversion also significantly (P < 0.01) reduced body weight. The findings support the idea that insufficient food intake in human pancreatic insufficiency may result from stimulation of ileal satiety mechanisms.

Erythromycin accelerates solid emptying at the expense of gastric sieving

Erythromycin accelerates gastric emptying by inducing antral contractions similar to phase III of interdigestive MMC. These powerful contractions are capable of forcing coin-sized indigestibles out of the stomach. In contrast, fed motility is associated with submaximal contractions that fragment (trituration) and propel solids while retaining large (> 0.5 mm) pieces for further size reduction (gastric sieving). In this study, using dogs with duodenal fistulas, we tested the hypothesis that erythromycin-induced acceleration of gastric emptying resulted in the passage of inadequately triturated (> 0.05 mm) chunks of solids into the duodenum. We found that gastric emptying was accelerated by erythromycin (vs 0.15 M NaCl control, P < 0.05). However, the percentage of chyme collected in the > 0.5-mm fraction was much greater (P < 0.01) in the erythromycin-treated experiments (63 +/- 9%) than the controls (7 +/- 1%). Correspondingly, while a fine gruel was passed during controls, under erythromycin infusion, most of the solids were emptied as large chunks virtually unchanged from the swallowed pieces. We conclude that erythromycin accelerates gastric emptying at the expense of gastric sieving.

Alterations in digestive function caused by pancreatic disease

Pancreatic exocrine secretion is regulated by a complex interaction of meal-stimulated neurohormonal reflexes. Pancreatic enzyme output must be reduced to less than 10 per cent of normal before fat absorption is appreciably impaired, proving that the pancreas secretes a large surplus of enzymes. Surgical therapy does not improve pancreatic exocrine insufficiency, and partial pancreatic resection frequently precipitates steatorrhea in patients with chronic pancreatitis. Therefore, pancreatic resection should be undertaken cautiously in patients who do not yet have clinically evident exocrine insufficiency. In most patients, oral pancreatic enzymes will control diarrhea secondary to steatorrhea. In others, concurrent administration of an H2 blocker is required to reduce gastric acidity and prevent enzyme inactivation in the stomach. Formulations with an acid-resistant coating are also effective in some patients. However, complete normalization of fat absorption with restoration of body weight and nutritional well-being requires careful management of multiple dietary and behavioral factors, as well as long-term follow-up. Unfortunately, this appears to be an elusive goal, as many patients with chronic pancreatitis continue to die of malnutrition.

The effect of bile diversion on satiety and fat absorption from liquid and solid dietary sources

In previous studies, liquid fat has been used to determine the effect of bile diversion on fat absorption. Since protein digests, in addition to bile salts, are capable of solubilizing lipids, we hypothesized that fat incorporated in the protein-rich matrix of solid food would be less sensitive to bile diversion than fat ingested as an oil or liquid. Using [3H]glycerol triether as a nonabsorbable fat recovery marker, we determined how much [14C]triolein was absorbed from solid (chicken liver) and liquid (margarine) dietary sources. After a standard liquid/solid meal with either the chicken liver or margarine labeled, midintestinal chyme was collected for 6 hr, extracted, and counted for 14C and 3H activity. Zero, eighty, or one hundred percent of endogenous bile was diverted. Fat absorption from both chicken liver and margarine was nearly complete by midintestine with 0% diversion and was little affected by diversion of 80% of bile. Complete biliary diversion significantly decreased fat absorption from margarine (87.9 +/- 4.4 to 37.2 +/- 9.2%, P less than 0.05) but reduced [14C]triolein absorption from chicken liver less consistently and insignificantly (78.8 +/- 6.9 to 43.9 +/- 10.6%). These data indicate that fat absorption is not solely dependent on bile and support the hypothesis that fat ingested in a cellular matrix is less dependent on bile than liquid fat. Using these same animals but with the midintestinal cannulas plugged to expose the distal intestine to unabsorbed luminal nutrients, we also demonstrated that bile diversion of an initial meal reduced food consumption at a meal offered 3 hr later.