Adrenergic modulation of small bowel haemodynamics in interdigestive motility state of man

OBJECTIVE

We previously reported a new application of semi-invasive laser-Doppler flowmetry (LDF) to record small intestinal haemodynamics in man under basal motor conditions, i.e. during phase I of the migrating motor complex (MMC). In the present study, we evaluated the complete MMC cycle and its haemodynamics in humans; specifically, adrenergic influence on blood flow in all three MMC phases was studied.

DESIGN

Twenty-one fasting healthy male volunteers (21-44 years) were studied during two complete MMC cycles: the first as control period, the second as experimental period with different adrenergic drugs or saline.

METHODS

Recording of LDF of intestinal blood flow was performed by attaching two single-fibre microprobes to a small intestinal manometry tube, which simultaneously monitored luminal pressure changes.

RESULTS

Clonidine and oxymetazoline, two alpha2-adrenoceptor agonists, significantly decreased blood flow during all phases of the MMC cycle. In contrast, the non-selective beta-adrenoceptor agonist isoprenaline induced phase II-like activity with a significant increase in blood flow. Propranolol, a beta-adrenoceptor antagonist, did not alter motility but decreased blood flow throughout the MMC cycle.

CONCLUSIONS

Both alpha- and beta-adrenergic mechanisms modifying small bowel haemodynamics are in operation throughout phases I, II and III of MMC. Our findings support the use of the semi-invasive LDF technique to measure drug-induced haemodynamic changes in the fasting gut.

Energy intake and appetite are suppressed by glucagon-like peptide-1 (GLP-1) in obese men

BACKGROUND

Peripheral administration of glucagon-like peptide-1 (GLP-1) for four hours, to normal weight and obese humans, decreases food intake and suppresses appetite.

OBJECTIVE

The aim of this study was to assess the effect of an eight hour infusion of GLP-1 on appetite and energy intake at lunch and dinner in obese subjects.

DESIGN

Randomised, blinded cross-over design with intravenous infusion of GLP-1 (0.75 pmol x kg(-1) min(-1)) or saline.

SUBJECTS

Eight obese (body mass index, BMI, 45.5 +/- 2.3 kg/m2) male subjects.

MEASUREMENTS

Ad libitum energy intake at lunch (12.00 h) and dinner (16.00 h) after an energy fixed breakfast (2.4 MJ) at 08.00 h. Appetite sensations using visual analogue scales, (VAS) immediately before and after meals and hourly in-between. Blood samples for the analysis of glucose, insulin, C-peptide, GLP-1 and peptide YY. Gastric emptying after breakfast and lunch using a paracetamol absorption technique.

RESULTS

Hunger ratings were significantly lower with GLP-1 infusion. The summed ad libitum energy intake at lunch and dinner was reduced by 1.7 +/- 0.5 MJ (21 +/- 6%) by GLP-1 infusion (P = 0.01). Gastric emptying was delayed by GLP-1 infusion, and plasma glucose concentrations decreased (baseline: 6.6 +/- 0.35 mmol/L; nadir: 5.3 +/- 0.15 mmol/L). No nausea was recorded during GLP-1 infusion.

CONCLUSIONS

Our results demonstrate that GLP-1 decreases feelings of hunger and reduces energy intake in obese humans. One possible mechanism for this finding might be an increased satiety primarily mediated by gastric vagal afferent signals.

Vasoactive intestinal peptide suppresses migrating myoelectric complex of rat small intestine independent of nitric oxide

The involvement of nitric oxide (NO) in the biological response to vasoactive intestinal peptide (VIP) on the migrating myoelectric complex (MMC) of small bowel and systemic arterial blood pressure was investigated in the rat. Animals were supplied with bipolar electrodes for electromyography of the small intestine and blood pressure was assessed by a pressure transducer connected to a carotid artery. In the first session, Nomega-nitro-L-arginine (L-NNA) was administered intravenously at 1, 2, 4 and 20 mg kg(-1). Effects of L-NNA at 1 and 20 mg kg(-1) were also studied after L-arginine 300 mg kg(-1). In the second session, intravenous infusion of VIP 500 pmol kg(-1) min(-1) was administered before and after L-NNA at 1 and 20 mg kg(-1). L-NNA at increasing doses stimulated myoelectric spiking of the small bowel until at 4 mg kg(-1) the MMC was disrupted and irregular spiking induced. Neither at 1 nor 20 mg kg(-1) did L-NNA affect the inhibitory motility response or decrease of blood pressure induced by VIP at a dose of 500 pmol kg(-1) min(-1). Our results show that effects of VIP on motility of the small intestine and systemic arterial blood pressure are direct and not dependent on NO as a common final link.

Serotonin stimulates migrating myoelectric complex via 5-HT3-receptors dependent on cholinergic pathways in rat small intestine

We have investigated the effect of 5-hydroxytryptamine (5-HT) and different 5-HT-receptor antagonists and atropine on the migrating myoelectric complex in the rat small intestine. Infusion of 5-HT dose-dependently shortened the interval between phase III of the migrating myoelectric complex (MMC). In untreated animals the interval in upper jejunum was 19.1 (16.0-22.1) min. At doses of 10 and 20 nmol kg-1 min-1, the interval decreased to 15.2 (12.0-18.4) and 10.2 (9.4-11.0) min, respectively. The 5-HT3-receptor antagonist ondansetron (0.5 mg kg-1) alone increased the MMC interval from 20.8 (15.1-26.5) to 33.9 (19.4-48.4) min. Neither methiothepin (0.5 mg kg-1) nor ketanserin (0.5 mg kg-1), selective for 5-HT1/5-HT2- and 5-HT2-receptors, respectively, changed the MMC interval. The 5-HT4-receptor antagonist GR 113808 (0.5 mg kg-1) disrupted the MMC and induced irregular spiking activity. Ondansetron and atropine antagonized the 5-HT-induced shortening of the MMC interval. Neither methiothepin nor ketanserin affected the response to 5-HT. GR 113808 did not block the response to 5-HT in half of the animals; however, in the remaining ones MMC was disrupted and irregular spiking induced. In conclusion, these results show that 5-HT dose-dependently stimulates the cycling of the MMC in the small intestine via 5-HT3-receptors and a cholinergic final pathway. Our findings encourage further studies on the role of the 5-HT3-receptor in the control of gastrointestinal motility.

Intraduodenal neuropeptide levels, but not plasma levels, vary in a cyclic fashion with the migrating motor complex

The neurohormonal control of the migrating motor complex (MMC) is not fully understood. The hypothesis of the present study was that neuropeptide levels might vary with the different phases of the MMC and that a similar variation might be found in the secretions of the gastrointestinal tract. Thus, plasma and intraduodenal concentrations of vasoactive intestinal peptide (VIP), somatostatin (SOM), substance P (SP) and neurokinin A (NKA) were determined by radioimmunoassay every 10 min during two complete MMC cycles in eight male subjects. For comparison, plasma motilin (MOT) concentrations were measured. Plasma concentrations of MOT (mean peak value +/- SEM; 39 +/- 6 pmol L-1), but none of the neuropeptides studied, showed a cyclic variation in plasma with the different phases of the MMC. Peak intraduodenal concentrations of VIP (79 +/- 23 pmol L-1), SOM (2437 +/- 432 pmol L-1) and SP (718 +/- 326 pmol L-1) occurred at or at the time point before the onset of phase III of the MMC. No such correlation was observed for NKA. These results demonstrate that intraduodenal but not plasma concentrations of the neuropeptides VIP, SOM and SP show an association with phase III of the MMC. The biological relevance of this finding is yet unclear, but the results raise the possibility that gut neuropeptides may regulate fasting motility through a luminal release.

Type I Helicobacter pylori shows Lewis(b)-independent adherence to gastric cells requiring de novo protein synthesis in both host and bacteria

Type I Helicobacter pylori strains frequently recognize the Lewisb (Leb) blood group antigen. This binding property and expression of the Leb oligosaccharide were required for adherence to fixed normal or pathologic gastric tissue. In contrast, both type I and type II strains adhered to cultured cells in the absence of the Leb epitope. For the gastric cell line AGS, adherence was significantly higher when viable type I strains were allowed to interact with viable AGS cells compared with fixed cells. The observation that chloramphenicol and cycloheximide, inhibitors of bacterial and eukaryotic protein synthesis, respectively, significantly reduced adherence of type I but not type II isolates suggests that in type I strains, adherence depends on the up-regulation of one or more host cell receptors triggered by the bacterium.

Glucagon-like peptide-1 retards gastric emptying and small bowel transit in the rat: effect mediated through central or enteric nervous mechanisms

This study investigated effects of glucagon-like peptide-1(7-36)amide (GLP-1) on gastric emptying, small intestinal transit, and contractility of smooth muscle strips in rats. GLP-1 at doses of 10 and 20 pmol/kg/min administered intravenously dose-dependently retarded transit of the small intestine (P < 0.001), while only the higher dose of 20 pmol/kg/min retarded gastric emptying (P < 0.01). GLP-1 at concentrations up to 10(-4) M did not affect the basal tone or contractility of the gastrointestinal muscle strips that were stimulated with electric field stimulation or acetylcholine. Our results demonstrate that small intestinal transit seems more sensitive than gastric emptying to inhibition by GLP-1 at physiologic levels in plasma. Furthermore, this inhibition appears to be mediated through central mechanisms rather than through peripheral actions. Thus, GLP-1 is suggested to inhibit gastric emptying and small intestinal transit through an indirect effect via central or enteric nervous mechanisms.

Glucagon-like peptide-1 retards gastric emptying and small bowel transit in the rat: effect mediated through central or enteric nervous mechanisms

This study investigated effects of glucagon-like peptide-1(7-36)amide (GLP-1) on gastric emptying, small intestinal transit, and contractility of smooth muscle strips in rats. GLP-1 at doses of 10 and 20 pmol/kg/min administered intravenously dose-dependently retarded transit of the small intestine (P < 0.001), while only the higher dose of 20 pmol/kg/min retarded gastric emptying (P < 0.01). GLP-1 at concentrations up to 10(-4) M did not affect the basal tone or contractility of the gastrointestinal muscle strips that were stimulated with electric field stimulation or acetylcholine. Our results demonstrate that small intestinal transit seems more sensitive than gastric emptying to inhibition by GLP-1 at physiologic levels in plasma. Furthermore, this inhibition appears to be mediated through central mechanisms rather than through peripheral actions. Thus, GLP-1 is suggested to inhibit gastric emptying and small intestinal transit through an indirect effect via central or enteric nervous mechanisms.

Glucagon-like peptide 1 increases the period of postprandial satiety and slows gastric emptying in obese men

The gut peptide glucagon-like peptide 1(7-36) amide (GLP-1) is released into the circulation after food intake. GLP-1 has been shown to have an incretin effect and inhibits gastrointestinal motility in humans. In rats, intracerebral administration of GLP-1 results in reduced food intake. Obese humans have been found to have an attenuated plasma GLP-1 response to a mixed meal. To approximate the physiologic state, GLP-1 or saline was administered intravenously and randomly at the beginning of a test meal served on a universal eating monitor to 6 obese subjects to test our hypothesis that GLP-1 influences termination of food intake (and thus food intake during a meal) and feelings of satiety in humans. As a marker for gastric emptying, 1.5 g acetaminophen was given at the start of the meal. Blood samples for analysis of acetaminophen, insulin, glucose, glucagon, and C-peptide were obtained. Hunger, fullness, and food choice were assessed with visual analogue scales and food-choice questionnaires. GLP-1 infusion resulted in a prolonged period of reduced feelings of hunger, desire to eat, and prospective consumption after the meal. The rate of gastric emptying was slower during infusion of GLP-1. Postprandial blood glucose concentrations were reduced during the GLP-1 infusion, but the amount of energy consumed, eating rate, and plasma concentrations of insulin, glucagon, and C-peptide were unchanged. GLP-1 given exogenously at the start of a meal did not seem to affect meal termination or the amount of food eaten. However, postprandial feelings of hunger decreased, suggesting that exogenous GLP-1 may influence feelings of hunger and satiety in humans.

Inhibitory effect of glucagon-like peptide-1 on small bowel motility. Fasting but not fed motility inhibited via nitric oxide independently of insulin and somatostatin

Effects of glucagon-like peptide-1 (GLP-1)(7-36)amide on fasted and fed motility in the rat small intestine were investigated in relation to its dependence on nitric oxide (NO), insulin, and somatostatin. Small bowel electromyography was performed using bipolar electrodes implanted 15, 25, and 35 cm distal to pylorus, and transit was studied with a radioactive marker. In the fasted state, GLP-1 (5-20 pmol kg-1min-1), reaching physiological plasma levels, prolonged the migrating myoelectric complex (MMC) cycle length along with slowed transit. This effect was antagonized by exendin(9-39)amide. The NO synthase inhibitor Nomega-nitro- L-arginine (L-NNA) also blocked the response to GLP-1, whereas L-arginine restored the response. Insulin (80-200 pmol kg-1min-1) induced irregular spiking, whereas somatostatin (100-500 pmol kg-1min-1) increased the MMC cycle length, independently of NO. In the fed state, GLP-1 (20-40 pmol kg-1min-1) reduced motility, an inhibition unaffected by L-NNA, whereas motility was stimulated by exendin(9-39)amide. Infusion of GLP-1 (20-100 pmol kg-1min-1) did not affect plasma insulin, but somatostatin was increased. In conclusion, GLP-1 seems to inhibit small bowel motility directly via the GLP-1 receptor. Inhibition of fasting motility is dependent of NO and not mediated via insulin or somatostatin, whereas inhibition of fed motility is independent of NO.

Importance of small bowel peptides for the improved glucose metabolism 20 years after jejunoileal bypass for obesity

BACKGROUND

Obese patients operated with jejunoileal bypass (JIB) have reduced plasma concentrations of insulin and glucose. Gastric inhibitory peptide/glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1) have been found to have a profound incretin effect in humans. The aim of the present study was to examine the long-term effect of JIB on glucose metabolism.

METHODS

Four groups (lean, nonoperated obese, obese 9 months after JIB and obese 20 years after JIB) of six females each were given a mixed meal (280 kcal). Plasma samples were obtained every 10 min for 60 min postprandially and were analyzed for glucose, insulin, GIP and GLP-1.

RESULTS

A reduction in body mass index (kg/m2) was seen for the two patient groups operated with JIB (12.1, at 9 months post-op; 13.1, at 20 years post-op). Surgery by JIB resulted in a reduction of glucose and insulin values. Concomitantly there was an elevation of postprandial GIP and GLP-1 plasma concentrations. In the obese subjects 20 years after JIB both fasting and postprandial GIP and GLP-1 values were markedly elevated compared with the other three groups; and plasma glucose and insulin concentrations were maintained at normal levels.

CONCLUSIONS

The improvement in glucose metabolism seen after JIB may be due to reduced insulin resistance after weight loss and/or increased levels of the incretin hormones GIP and GLP-1. Progressively, elevated levels of GIP and GLP-1 seem to be necessary to maintain glucose homeostasis at long-term follow-up after this procedure.

Concentration-dependent stimulation of intestinal phase III of migrating motor complex by circulating serotonin in humans

1. The influence of circulating 5-hydroxytryptamine (serotonin) on small intestinal motility was investigated in healthy volunteers. 2. Small intestinal motility was studied by means of a constantly perfused multi-channel manometry tube, connected to a computer system. 3. Intravenous infusions of either 5-hydroxytryptamine at increasing doses or saline were given over a period of 4 h. 4. 5-Hydroxytryptamine infusion dose-dependently increased plasma 5-hydroxytryptamine from approximately 2 to 10 and 25 nmol/l respectively, as well as urinary excretions of 5-hydroxytryptamine and 5-hydroxyindole acetic acid, a major 5-hydroxytryptamine metabolite. 5. The number of phase III of the migrating motor complex originating in the small intestine was dose-dependently increased by 5-hydroxytryptamine, and found to correlate to the plasma concentration of 5-hydroxytryptamine. The fraction of phase III also increased at the expense of phase II activity. In addition, 5-hydroxytryptamine increased the motility index, propagation velocity of phase III activity and the amplitude of contractions during phase III. 6. Whereas the low dose of 5-hydroxytryptamine (15 nmol.min-1.kg-1) had no haemodynamic effects, an increase in heart rate by approximately 20 beats/min, without change in blood pressure, was observed at the higher dose (60 nmol.min-1.kg-1). Respiratory parameters did not change during infusion of 5-hydroxytrytamine at either dose. 7. In conclusion, elevation of circulating 5-hydroxytryptamine by intravenous infusion results in more frequent and faster propagating migrating motor complexes in the human small intestine during the inter-digestive period.

Distal small bowel hormones: correlation with fasting antroduodenal motility and gastric emptying

The aim of the present study was to study the interdigestive motor complex (MMC), distal small intestinal hormones, and gastric emptying in normal-weight and obese subjects before and after jejunoileal bypass (JIB). Therefore, fasting antroduodenal motility, gastric emptying, and RIA for motilin (MOT), neurotensin (NT), peptide YY (PYY), and glucagon-like peptide-1 (GLP-1) was performed in nine obese subjects before (BMI 42 +/- 4 kg/m2) and nine months after (BMI 31 +/- 4) JIB, and in two groups of nine age- and sex-matched controls (BMI 23 +/- 1 and 21 +/- 1). The rate of gastric emptying was faster in obese subjects and GLP-1 lower compared to normal-weight controls. After JIB, fewer phase III of the MMC were observed; fasting levels of PYY were elevated during the MMC; postprandial levels of NT, PYY, and GLP-1 were elevated; and gastric emptying was delayed. Our results suggest that there may be an association between an impaired GLP-1 response after food intake and obesity, and after JIB, PYY seems to regulate interdigestive motility while GLP-1 may regulate early gastric emptying.

Nociceptive inhibition of migrating myoelectric complex by nitric oxide and monoaminergic pathways in the rat

This study investigated the role of nitric oxide (NO) and adrenergic and dopaminergic mechanisms in reflex inhibition of the migrating myoelectric complex (MMC) after intraperitoneal administration of acid in rats. Acid instilled immediately after an activity front inhibited the migrating complex and prolonged the cycle length from 13.0 +/- 0.7 to 98.5 +/- 17.2 min (P < 0.001). Administration of N omega-nitro-L-arginine, reserpine, or guanetidine before acid decreased the prolonged cycle length to 18.1 +/- 2.8 (P < 0.001), 19.0 +/- 2.0 (P < 0.001), and 27.5 +/- 9.3 min (P < 0.001), respectively. Similarly, haloperidol given before acid shortened the prolonged cycle length to 46.7 +/- 5.2 min (P < 0.05). There was no effect of phentolamine in combination with propranolol or hexamethonium given alone. After intraperitoneal instillation of acid there was an increase in the plasma levels of somatostatin and a decrease of calcitonin gene-related peptide, but there was no change of neuropeptide Y, vasoactive intestinal peptide, substance P, neurokinin A, or neurotensin. The results indicate that NO and adrenergic, dopaminergic, and somatostatinergic mechanisms cooperate in inhibiting the MMC after nociceptive stimulation of the peritoneum.

Impaired gastric emptying in children with repaired esophageal atresia: a controlled study

BACKGROUND

Scintigraphy is considered the "gold standard" for investigating gastric emptying. The lack of standards regarding registration technique and meal composition has been a problem especially in pediatric patients.

METHODS

In this study, gastric emptying of a solid meal was assessed by scintigraphy in 10 patients with repaired esophageal atresia (5 to 10 years old), and the results were compared with those in 11 healthy control children (5 to 11 years old). The meal consisted of pancakes with a fixed energy composition labeled with Tc-99m. Fractional meal retention values were plotted as a function of time.

RESULTS

Half-emptying time and lag phase values were longer in the patient group, whereas the emptying rate was slower and the retention values at 60 and 90 minutes were higher than in the control group. Extremely long lag phase and slow emptying rates were seen in two patients with reflux symptoms and abdominal complaints. Gastric emptying in healthy children has not previously been studied by scintigraphy. The results of this study show that values for gastric emptying of solids in healthy children correspond well to those reported in healthy adults.

CONCLUSION

Scintigraphy is an easy and reliable method for gastric emptying studies in children. The radioactive dose can be kept very low, which makes it a safe method even for pediatric patients. Delayed gastric emptying can occur in patients who have repaired esophageal atresia, and may be associated with reflux symptoms and abdominal complaints.

Increased luminal nitric oxide in inflammatory bowel disease as shown with a novel minimally invasive method

BACKGROUND

The production of nitric oxide (NO) is increased in ulcerative colitis, as shown by bioassays of NO synthase activity in mucosal biopsy specimens. We wanted to develop a less invasive method for measurement of NO directly in the rectum in patients with inflammatory bowel disease (IBD).

METHODS

We studied 10 patients with active ulcerative colitis, 6 with active Crohn's disease, 6 with non-active ulcerative colitis, and 24 controls without inflammation A tonometer balloon catheter was inserted in the rectum and inflated with 5 ml of NO-free air. After 15 min of incubation the sample was extracted, and the NO concentration was immediately analysed with a chemiluminescence technique.

RESULTS

Patients with active disease had greatly increased concentrations of NO in the rectum as compared with controls and patients with non-active disease.

CONCLUSIONS

During inflammation in the large intestine increased amounts of NO are released from the mucosa. Measurements of NO directly in the rectum could be of help in further understanding the role of this gas in IBD. Moreover, it is tempting to speculate that this minimally invasive method could be clinically useful as a diagnostic tool and in monitoring the effect of therapy.

Glucagon-like peptide-1 in the pathogenesis of obesity

The recently discovered gut peptide glucagon-like peptide-1 (GLP-1) is one of many peptides implicated in the short-term regulation of appetite. GLP-1 is a 30-amino-acid peptide that is produced in and secreted from the L cells of the intestinal mucosa after intake of a mixed meal. The amino acid sequence of GLP-1 is highly conserved and all mammals studied to date have identical GLP-1 sequences. GLP-1 receptors have been found in the lung and stomach, and binding of GLP-1 to skeletal muscle and fat cells has been demonstrated. At physiological plasma levels GLP-1 inhibits meal- and pentagastrin-induced gastric acid secretion. In addition, gastric emptying is delayed. Plasma GLP-1 is acutely elevated in normal-weight subjects after a meal, but obese subjects seem to have an attenuated GLP-1 release in response to meals. Consequently, GLP-1 may be a candidate for meal termination and intermeal satiety by either peripheral or central pathways. In terms of the importance of GLP-1 in the pathogenesis of obesity, research points in the direction of a vicious circle where overfeeding results in a down-regulation of postprandial GLP-1 release, which may result in the consumption of a larger amount of calories to elicit a "normal" GLP-1 satiety signal, thus perpetuating the obese state.

Mediation of irregular spiking activity by multiple neurokinin-receptors in the small intestine of the rat

1. We have studied the small intestinal myoelectric response to the natural tachykinins substance P (SP), neurokinin A (NKA), neurokinin B (NKB), and the neurokinin-receptor selective agonists substance P methyl esther (SPME), [beta-Ala8]neurokinin A 4-10, and senktide in conscious rats. 2. The effects of the agonists were studied before and after administration of the selective neurokinin2 (NK2)-receptor antagonist MEN 10,627. 3. Under basal conditions SP, NKA, NKB, as well as the selective NK1-receptor agonist SPME, the NK2-receptor agonist [beta-Ala8]NKA 4-10, and the NK3-receptor agonist senktide, disrupted the interdigestive rhythm with regularly recycling migrating myoelectric complexes and induced a phase II-like irregular spiking activity. 4. MEN 10,627 given alone did not affect the interdigestive rhythm. 5. MEN 10,627 inhibited the response to [beta-Ala8]NKA 4-10 but not to SP, SPME, NKA, NKB or senktide. 6. It is concluded that not only NK2 receptors, but also other receptors, such as NK1 and NK3 receptors, may mediate the motility-stimulating action of different tachykinins in vivo. 7. It is further concluded that MEN 10,627 exerts a selective NK2-receptor antagonism, and may be a valuable tool for assessing the functional role of NK2-receptors in gastrointestinal physiology.

Neurokinin A increases duodenal mucosal permeability, bicarbonate secretion, and fluid output in the rat

The aim of this study was to examine the integrative response to neurokinin A (NKA) on duodenal mucosal permeability, bicarbonate secretion, fluid flux, and motility in an in situ perfusion model in anesthetized rats. Intravenous infusion of NKA (100, 200, and 400 pmol.kg-1.min-1) induced duodenal motility. Furthermore, duodenal mucosal bicarbonate secretion, fluid output, and mucosal permeability increased in response to NKA. Pretreatment with the nicotinic antagonist hexamethonium did not change the response in any of the parameters investigated, whereas the NK2-receptor antagonist MEN 10,627 effectively inhibited all responses to NKA. Indomethacin induced duodenal motility and stimulated bicarbonate secretion. In indomethacin-treated rats, NKA further increased motility but decreased indomethacin-stimulated bicarbonate secretion by 70%. The NKA-induced increase in mucosal permeability was unaltered by indomethacin. It is concluded that NKA not only induces motility but also increases mucosal permeability and fluid output. Furthermore, the neuropeptide may have both stimulative and inhibitory effects on bicarbonate secretion. All responses to NKA are dependent on NK-2 receptor activation but are not mediated through nicotinic receptors.

Increased nitric oxide production in collagenous and lymphocytic colitis

The production of nitric oxide (NO) is increased in active ulcerative colitis and in Crohn's disease. We have studied NO production in collagenous colitis (CC) and lymphocytic colitis (LC), both of which are inflammatory bowel disorders of unknown aetiology. NO levels were measured directly in gas sampled from the colon during colonoscopy. Plasma levels of NO metabolites (nitrate/nitrite) were also measured. Luminal NO levels were more than 100 times higher in patients with CC compared with controls. In addition, plasma levels of nitrate/nitrite were increased in the patients as compared with controls. Measurements of NO directly in the colon or its oxidation products in plasma may be a helpful tool in further understanding the role of NO in the pathophysiology of CC and LC. Moreover, it is tempting to speculate that these measurements could be clinically useful in the diagnosis and therapy monitoring of these two inflammatory bowel diseases.

Tachykinins influence interdigestive rhythm and contractile strength of human small intestine

The effect of the putative enteric neurotransmitters neurokinin A and substance P were investigated on human small intestinal motility. Either neurokinin A, at doses of 6-25 pmol/kg/min, or substance P at doses of 1-6 pmol/kg/min were administered intravenously to healthy volunteers over 4 hr. Neurokinin A dose-dependently increased the fraction of phase II of the migrating motor complex, contraction frequency, motility index, and amplitude of contractions. At the highest dose, neurokinin A induced a phase II-like pattern, disrupting the migrating myoelectric complex. Substance P dose-dependently increased phase II of the migrating motor complex. The contraction frequency increased slightly at the highest dose, but neither motility index nor contraction amplitude changed. It is concluded that neurokinin A and substance P stimulate small intestinal motility in man, and it can be speculated that they play a role in the control of human small intestinal motility.

Endotoxin actions on myoelectric activity, transit, and neuropeptides in the gut. Role of nitric oxide

The lipopolysaccharide (endotoxin) of gram-negative bacteria has systemic effects in animals and man. Our aim was to investigate the effects of E. coli lipopolysaccharide on motility and transit through the small intestine in rats and to analyze plasma and tissue concentrations of intestinal neuropeptides. When lipopolysaccharide (20-160 micrograms/kg) was administered intravenously, the migrating myoelectric complex was replaced by spike bursts accompanied by rapid transit. Tissue concentrations of substance P and neurokinin A decreased, while plasma levels of calcitonin gene-related peptide increased N omega-Nitro-L-arginine, N omega-L-arginine methyl ester, dexamethasone, or indomethacin prevented these changes in myoelectric activity and tissue contents of neuropeptides. All of these compounds, except indomethacin, prevented the increased rate of transit. Thus, lipopolysaccharide changes motility through the nitric oxide and arachidonic pathways, resulting in rapid transit through the gut.

Semi-invasive laser-Doppler flowmetry technique. New application for recordings of hemodynamics in combination with manometry of human small intestine

A small-bowel manometry tube was supplied with two single-fiber microprobes, which recorded blood flow in the proximal small intestine by the laser-Doppler flowmetry (LDF) technique. In all experiments, saline was infused intravenously as control during the first migrating motor complex (MMC) cycle, and a drug or another saline control given intravenously during the second MMC cycle. Recordings were performed during phase 1 of MMC, i.e. when motor pattern showed quiescence. Adrenaline increased blood perfusion values by 140% in proximal duodenum and 95% in distal duodenum. The alpha 2-adrenoceptor agonist clonidine decreased the corresponding values by 34 and 25%, respectively, while oxymetazoline decreased perfusion by 33 and 44% at the same levels. The beta-adrenoceptor agonist isoprenaline increased blood perfusion values by 172% in the proximal duodenum and 194% in the distal duodenum, whereas the antagonist propranolol decreased the corresponding values by 45 and 52%, respectively. In a separate group of subjects, propranolol was given after adrenaline. The increase in blood perfusion regularly seen after adrenaline was blocked after propranolol administration. In conclusion, our findings validate semi-invasive LDF technique for studies of hemodynamics in human small intestine under basal motor conditions and in drug-induced blood flow changes.

Tachykinins stimulate lipid peroxidation mediated by free radicals in gastrointestinal tract of rat

Tissue concentrations of malondialdehyde in the gastrointestinal tract of the rat were quantified as indicators of lipid peroxidation and tissue damage after challenge with tachykinins and after pretreatment with allopurinol. Neurokinin A, neurokinin B, and substance P given intravenously during 30 min increased the production of malondialdehyde in the stomach, duodenum, jejunum, and colon in a dose-dependent manner at doses from 100 to 400 pmol/kg/min (P < 0.05-0.01). However, the stomach seemed less responsive to the tachykinin challenge. For comparison, a similar dose-dependent increase of malondialdehyde was found in the liver and lung, with more pronounced effects of neurokinin B (P < 0.05-0.01). Pretreatment with allopurinol, 10 mg/kg, significantly reduced malondialdehyde responses to tachykinin challenge in intestinal tissues (P < 0.001). In conclusion, elaboration of malondialdehyde is suggested to reflect the ability of gastrointestinal tissues to react to tachykinins at high concentrations with liberation of free radicals as part of an inflammatory reaction.