Stimulation of pyloric motility by intraduodenal dextrose in normal subjects

Effects of glyceryl trinitrate on the pyloric motor response to intraduodenal triglyceride infusion in humans

The retardation of gastric emptying induced by infusion of triglyceride into the small intestine is associated with suppression of antral pressure waves and stimulation of basal pyloric tone in combination with phasic pressure waves localized to the pylorus. The role of nitric oxide (NO) mechanisms in the control of pyloric motility was evaluated in 12 healthy male subjects (21-43 years), using the NO donor glyceryl trinitrate (GTN). Antropyloric pressures were measured with a manometric assembly incorporating nine sideholes, spanning the antrum and proximal duodenum, and a pyloric sleeve sensor. On separate days, an intraduodenal triglyceride infusion (10% intralipid at 1 mL min-1) was started during antral phase I activity and continued for 60 min. On one of the days GTN (600 micrograms) was given sublingually 20 min after start of the triglyceride infusion. The tonic pyloric motor response to triglyceride [5.6 (SEM 0.8,) vs. 2.7 (1.3) mmHg, P < 0.001] and both the number 3.2 (0.2) vs. 2.2 (0.2) min-1, P < 0.05] and amplitude [40 (4) vs. 27 (5) mmHg, P < 0.05] of phasic isolated pyloric pressure waves were reduced by GTN. These observations suggest that NO mechanisms are involved in the regulation of pyloric motor activity in humans.

Nitric oxide mediates mechano- and chemoreceptor-activated intestinal feedback control of gastric emptying

The effect of nitric oxide (NO) synthase inhibition on the gastric emptying of nutrient and nonnutrient meals was investigated in nine dogs. The inhibition of NO synthase delayed the gastric emptying time of both nutrient and nonnutrient meals, but the percentage delay of nutrient meals was significantly greater than that of nonnutrient meals. The inhibition of NO synthase during the emptying of nonnutrient meals enhanced mainly the amplitude of antral, pyloric, and distal duodenal contractions. However, NO synthase inhibition during the emptying of nutrient meals stimulated several spatial and temporal parameters of gastropyloroduodenal contractions. We conclude that NO is one of the neurotransmitters of intestinal feedback that regulates the gastric emptying of both nutrient and nonnutrient meals. The nature and intensity of intestinal feedback by the stimulation of both chemo- and mechanoreceptors by nutrient meals is different from that by the stimulation of mechanoreceptors only by the nonnutrient meals.

Functional characteristics of canine pylorus in health, with pyloroplasty, and after pyloric reconstruction

The aim was to determine whether pyloroplasty decreases the strength of pyloric contractions and speeds gastric emptying of solids, while subsequent pyloric reconstruction restores these abnormalities to the control. In conscious dogs, pyloroplasty decreased the strength of pyloroduodenal pressure waves measured with a perfused sleeve sensor [mean +/- SEM pyloroduodenal motility index: control (N = 7) = 1116 +/- 351 mm Hg x sec/10 min; pyloroplasty (N = 7) = 43 +/- 19 mm Hg x sec/10 min; P < 0.05], and caused rapid gastric emptying of solids measured scintigraphically (mean +/- SEM half-emptying time: control = 246 +/- 14 min, pyloroplasty = 176 +/- 16 min; P < 0.05). The frequencies of pyloroduodenal waves and gastric emptying of liquids, however, were unchanged. Pyloric reconstruction restored the postpyloroplasty patterns to the control. In conclusion, pyloroplasty decreased the strength of pyloroduodenal contractions and sped gastric emptying of solids, while pyloric reconstruction restored the altered patterns to the control.

Gastric emptying and release of incretin hormones after glucose ingestion in humans

This study investigated in eight healthy male volunteers (a) the gastric emptying pattern of 50 and 100 grams of glucose; (b) its relation to the phase of interdigestive motility (phase I or II) existing when glucose was ingested; and (c) the interplay between gastric emptying or duodenal perfusion of glucose (1.1 and 2.2 kcal/min; identical total glucose loads as orally given) and release of glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1(7-36)amide (GLP-1), C-peptide, insulin, and plasma glucose. The phase of interdigestive motility existing at the time of glucose ingestion did not affect gastric emptying or any metabolic parameter. Gastric emptying of glucose displayed a power exponential pattern with a short initial lag period. Duodenal delivery of glucose was not constant but exponentially declined over time. Increasing the glucose load reduced the rate of gastric emptying by 27.5% (P < 0.05) but increased the fractional duodenal delivery of glucose. Both glucose loads induced a fed motor pattern which was terminated by an antral phase III when approximately 95% of the meal had emptied. Plasma GLP-1 rose from basal levels of approximately 1 pmol/liter of peaks of 3.2 +/- 0.6 pmol/liter with 50 grams of glucose and of 7.2 +/- 1.6 pmol/liter with 100 grams of glucose. These peaks occurred 20 min after glucose intake irrespective of the load. A duodenal delivery of glucose exceeding 1.4 kcal/min was required to maintain GLP-1 release in contrast to ongoing GIP release with negligibly low emptying of glucose. Oral administration of glucose yielded higher GLP-1 and insulin releases but an equal GIP release compared with the isocaloric duodenal perfusion. We conclude that (a) gastric emptying of glucose displays a power exponential pattern with duodenal delivery exponentially declining over time and (b) a threshold rate of gastric emptying of glucose must be exceeded to release GLP-1, whereas GIP release is not controlled by gastric emptying.

Role of antral intramural neural pathways in control of gastric emptying in the pig

1. The role of antral intramural pathways in the control of antropyloric motility and gastric emptying was evaluated in five conscious pigs equipped with chronic gastric and duodenal cannulae. Neural pathways were divided by transection and re-anastomosis of the antrum 2 cm proximal to the pylorus. Concurrent measurements of gastric emptying, transpyloric flow and antropyloric motility were performed before and 6 weeks after surgery. 2. Antral transection retarded gastric emptying, only 36% of 1000 ml saline being emptied in 30 min compared with 62% before transection. Transection did not alter the number of transpyloric flow pulses (22.0 +/- 4.0 cf. 24.4 +/- 3.2 pre-transection), but reduced (P < 0.01) the volume of flow pulses substantially (8.6 +/- 0.4 cf. 18.7 +/- 1.5 ml pre-transection). 3. Antral transection was associated with a reduction in the rate of distal antral pressure waves (P < 0.05), but no alteration in the rate of phasic low level pressurization of the entire gastric content by gastric contractions (gastric common cavity pressure waves). However, transection was associated with a significant (P < 0.05) shortening of the interval between the onset of gastric common cavity pressure waves, and the onset of lumen-occlusive pyloric pressure waves generated by the same contraction sequence (3.2 +/- 0.3 cf. 7.9 +/- 0.6 s). 4. Transection did not alter the inhibition of antral pressure waves, stimulation of localized pyloric pressure waves, and retardation of gastric emptying produced by infusion of 25% dextrose into the duodenum. 5. These studies suggest that antral intramural nerves regulate the emptying of liquids from the stomach by modulating the timing of pyloric closure in relation to phasic gastric antral and corpus contractions. 6. Distal antral intramural neural pathways do not appear to play a major role in the suppression of antral motor activity produced by duodenal glucoreceptors.

Mechanics of pulsatile transpyloric flow in the pig

1. In eight conscious pigs equipped with gastric and duodenal cannulae, the relationship of transpyloric flow to gastro-duodenal motor events was evaluated during gastric emptying of 1000 ml of saline. Rates of liquid gastric emptying were correlated with pressures at the antrum, pylorus and duodenum, recorded by a sleeve sensor and multiple perfused side-holes. Transpyloric flow was recorded concurrently by continuous collection and weighing of the duodenal effluent. 2. In three pigs the above measurements were repeated during concurrent videofluoroscopy of gastric emptying after adding 100 ml of liquid barium to the gastric instillate. 3. The mean volume of saline emptied in 30 min was 627 +/- 51.2 ml. Pulsatile flow accounted for 71% of total emptying. Pulses had a mean flow rate of 3.9 +/- 0.44 ml s-1. Most flow pulses (59%) occurred during the first 5 min of emptying. 4. Distinctive, low-amplitude (4.8 +/- 0.33 mmHg), relatively long-lasting (15.8 +/- 0.46 s) antral pressure waves were associated with 58% of flow pulses. In all antral pressure recording points, the first and longest duration component of these pressure waves had an identical timing, amplitude and waveform consistent with pressurization of the entire antrum-gastric cavity. 5. Videofluoroscopy and concurrent manometry showed that these antral common cavity pressure waves were associated with non-lumen-occlusive contractions of the gastric wall, initially observed at the corpus which propagated down to the pylorus; 93% of these contractions became lumen occlusive in the terminal antrum and pylorus when pressure waves of a unique pattern for each recording point were recorded at this level. 6. The onset of 68% of the flow pulses which accounted for 62% of pulsatile emptying occurred in the interval (mean 7.9 +/- 0.65 s) between the onset of the common cavity wave and the onset of localized, lumen-occlusive distal antral-pyloric pressure waves. 7. These findings indicate that in the pig, pulsatile emptying of non-nutrient liquids into the duodenum occurs predominantly during the non-lumen-occlusive stage of a propagated gastric contraction, which is recognisable as a common cavity pressure wave. This is a previously inadequately recognized pattern of gastric pumping.

Effect of drink temperature on antropyloroduodenal motility and gastric electrical activity in humans

There is little information on the motor mechanisms underlying the effects of meal temperature on gastric emptying. The effects on antropyloric pressures and the surface electrogastrogram of ingesting drinks at 4 degrees C, 37 degrees C, and 50 degrees C (350 ml normal saline and 50 ml low calorie (7 kj) orange cordial) given in randomised order were measured over 60 minutes in 12 normal volunteers (10 men and 2 women, aged 18-55 years). The warm and cold drinks suppressed antral pressure waves (p < 0.05), altered the organisation of antropyloric pressure waves (p < 0.05), stimulated isolated pyloric pressure waves (p < 0.05), and increased electrogastrogram frequency (p < 0.05) when compared with the 37 degrees C drink. These changes were greatest in the first 30 minutes after ingestion and greater (p < 0.05) with the 4 degrees C drink. Temperature has major effects on postprandial antropyloroduodenal motility in normal subjects. Both cold and warm drinks stimulate a pattern of motility associated with retardation of transpyloric flow.

Effect of cisapride on myoelectrical and motor responses of antropyloroduodenal region during intraduodenal lipid and antral tachygastria in conscious dog

The myoelectrical and motor response of the antropyloroduodenal region to intraduodenal nutrient stimulation or antral tachygastria represent useful models for, respectively, physiological and pathophysiological gastric stasis to test the efficacy of prokinetic drugs. We evaluated the effects of an intravenous bolus of cisapride (0.63 mg/kg) on the myoelectrical and motor response of the antropyloroduodenal region to an intraduodenal triglyceride emulsion (10% Intralipid, 0.5 ml/min) or antral tachygastria in conscious dogs. Intraduodenal lipid suppressed antral motility (P < 0.05, compared to intraduodenal saline) and stimulated phasic pyloric contractions (P < 0.01, compared to intraduodenal saline), a motor pattern known to be associated with delayed gastric emptying. During intraduodenal lipid stimulation cisapride virtually abolished all isolated pyloric motor events (P < 0.05) and stimulated antral and duodenal motility (P < 0.05 for both) and antropyloroduodenal coordination (65% versus 15%; P < 0.05). Antral tachygastria was associated with a higher number of isolated pyloric motor events in the fasted state [0.8 (0.7-1.1) per minute versus 0.2 (0-0.3) per minute; P < 0.05], but not during intraduodenal lipid stimulation [1.1 (0.9-1.7) per minute versus 1.2 (1.0-1.9) per minute; NS]. Cisapride decreased the number and duration of spontaneous episodes of antral tachygastria during intraduodenal saline and lipid infusion (P < 0.05 for both) and abolished the tachygastria-associated motor patterns. Cisapride induced a 20% decrease in the antral slow-wave frequency during intraduodenal saline and lipid, irrespective of gastric pacemaker rhythm. We conclude that: (1) cisapride overcomes feedback from small intestinal lipid receptors on myoelectrical and motor activities of the antropyloroduodenal region and decreases antral slow-wave frequency, and (2) cisapride inhibits antral tachygastria and tachygastria-associated motor patterns. These effects may contribute to the effective gastrokinetic properties of cisapride in physiological and certain forms of pathophysiological gastric stasis.

Stereospecific effects of intraduodenal tryptophan on pyloric and duodenal motility in humans

BACKGROUND

L-Tryptophan delays gastric emptying in animals to a greater extent than D-tryptophan, but none of the possible motor mechanisms responsible for this stereospecific effect have been evaluated.

METHODS

In 11 healthy volunteers antropyloroduodenal pressures were recorded in the fasted state with a sleeve/sidehole manometric assembly during 20-min intraduodenal infusions (2 ml.min-1) of isotonic L- and D-tryptophan (50 mM, pH 5.7) and normal saline (pH 5.5), given in randomized order.

RESULTS

Intraduodenal L-tryptophan increased basal pyloric pressure (p < 0.05), whereas D-tryptophan had no effect. In contrast, L- and D-tryptophan both stimulated (p < 0.05) localized phasic pyloric pressure waves, and there was no significant difference in the responses. The number of duodenal pressure waves was greater during infusion of L-tryptophan than during D-tryptophan (p < 0.05).

CONCLUSION

We conclude that intraduodenal tryptophan has stereospecific effects on pyloric and duodenal motility. Although the precise contribution of these differential effects to gastric emptying remains to be clarified, they may be partially responsible for the differences in gastric emptying of D-tryptophan and L-tryptophan.

Modulation of pumping function of gastric body and antropyloric contractions

Gastric and antropyloric phasic contractions control transpyloric pulsatile flow, the major mechanism of gastric emptying. Both the occurrence and patterning of phasic gastric contractions are highly modulated by intestinal feedback mechanisms, with resultant variation in gastric emptying. The observed patterns of these contractions can only be plausibly explained by the action of neural influences on gastric motility. These influences derive from several mechanisms driven by intestinal feedback, central nervous system controls, and higher centers, with transmission of signals via intrinsic enteric pathways and extrinsic nerves. It is suggested that the occurrence and patterning of gastric phasic contractions depend on the spatial specificity and local modulation of the intensity of neural stimulation of gastric muscle. The resultant strength of contraction determines the occurrence and timing of lumen occlusion relative to adjacent regions. The timing of lumen occlusion in adjacent regions may be the major determinant of mechanical outcome.

Stereospecific effects of tryptophan on gastric emptying and hunger in humans

The amino acid tryptophan (tryp) is a potent inhibitor of gastric emptying in both animals and humans. Animal studies suggest that this effect may be specific for the L-enantiomer. The effects of D- and L-tryptophan on gastric emptying, intragastric distribution and appetite in humans were evaluated. Ten volunteers ingested 300 mL of either L-tryp (50 mmol/L), D-tryp (50 mmol/L) or normal saline labelled with 99mTc sulfur colloid on three occasions, separated by between 3 and 7 days. Hunger and fullness were measured with a visual analogue scale at -2, 15, 30 and 60 min after ingestion of each drink. Saline emptied faster from the stomach than both L-tryp and D-tryp (P < 0.05) and D-tryp emptied faster than L-tryp (P < 0.005). Emptying from the proximal stomach was fastest for saline (P < 0.05) and faster for D-tryp than L-tryp (P < 0.005). Emptying from the distal stomach was faster for saline than both D- and L-tryp (P < 0.05). A reduction in hunger (P < 0.05) and a non-significant trend for an increase in fullness were observed after all three drinks. At 60 min, fullness was greater after L-tryp than after ingestion of D-tryp (P < 0.01). These observations indicate that the effect of tryptophan on gastric emptying in humans is stereospecific, consistent with the concept that stereospecific receptors for tryptophan exist in the human small intestine.

Effects of duodenal distention on fasting and postprandial antropyloroduodenal motility in humans

BACKGROUND/AIMS

Mechanoreceptors in the proximal small intestine may play an important role in the regulation of gastric emptying. Balloon distention of the duodenum causes fundic relaxation. The purpose of the present study was to determine the effect of stimulation of duodenal mechanoreceptors on both fasting and postprandial antropyloroduodenal motility in humans.

METHODS

Antropyloroduodenal pressures were recorded in 12 healthy volunteers with a sleeve-sidehole assembly, incorporating two balloons 5 and 20 cm distal to the pylorus. Duplicate proximal and distal duodenal balloon distensions with 10, 20, and 30 mL of air for 2.5 minutes were performed separately and in randomized order both during fasting and after a meal.

RESULTS

During fasting, proximal and distal distention at all volumes increased the number of isolated pyloric pressure waves (P < 0.05) and basal pyloric pressure (P < 0.05), and the response to proximal distention was greater (P < 0.05). Postprandially, proximal and distal distention increased basal pyloric pressure (P < 0.05) with a greater response to proximal distention (P < 0.05), but had no effect on isolated pyloric pressure waves. Both during fasting and postprandially, there were more synchronous and less antegrade antral waves during distention (P < 0.05). The number of duodenal pressure waves increased during proximal (P < 0.05) but not distal distention.

CONCLUSIONS

Stimulation of duodenal mechanoreceptors by balloon distention has significant and region-dependent effects on antropyloroduodenal motility that vary between fasting and postprandial states.

Postprandial antropyloroduodenal motility and gastric emptying in gastroparesis--effects of cisapride

There is little information about the organisation of antroduodenal contractions or pyloric motility in patients with gastroparesis. The mechanisms responsible for the acceleration of gastric emptying by cisapride in patients with gastroparesis are also poorly understood. Simultaneous manometric and scintigraphic recordings were performed in 12 patients with gastroparesis and nine healthy volunteers before and after cisapride administration. Antropyloroduodenal pressures were recorded with a sleeve/side hole manometric assembly and gastric emptying with a scintigraphic method. Thirty minutes after the solid component of the test meal had begun to empty from the stomach all subjects received 5 mg cisapride intravenously over 10 minutes and recordings continued for a further 60 minutes. In the 30 minutes before cisapride there was no significant difference in the number of antral pressure waves (median 20 v 33, NS), basal pyloric pressure, or the number of isolated pyloric pressure waves between patients and volunteers, but the number of antral waves of extent > or = 6 cm (median 1 v 5, p < 0.05) was less in the patients, as was gastric emptying (8% v 20%, p < 0.05). In the patients, there was no change in the number of antral waves after cisapride, but there was an increase in the number of antral waves > or = 6 cm in extent (median 7 v 1, p < 0.05) and in the rate of gastric emptying (26% v 8%, p < 0.01). In the healthy subjects, cisapride increased gastric emptying (31% v 20%, p < 0.05), but reduced the number of antral waves (10 v 33, p < 0.05). Cisapride had no significant effect on the number of antral waves of extent more than or equal to 6 cm (11 v 5, NS). The number of isolated pyloric pressure waves decreased after cisapride (4 v 11, p < 0.05). There was a relationship between gastric emptying and the number of antral pressure waves of extent more than or equal to 6 cm in both the patients (r=0.38, p<0.05) and healthy subjects (r=0.05, p<0.01). There was no significant relationship between gastric emptying and the number of antral waves. It is concluded that disturbance of the relationship between antral, pyloric, and duodenal pressure waves is a major abnormality of postprandial gastric motor function in patients with gastroparesis. The stimulation of antral pressure waves of extent more than or equal to 6 cm may contribute to the acceleration of gastric emptying produced by cisapride in patients with gastroparesis and in normal subjects.

Pyloric motility and liquid gastric emptying during barostatic control of gastric pressure in pigs

1. In conscious pigs, intragastric pressure was controlled by a water barostat such that the gastroduodenal pressure gradient was always positive with the barostat set above 15 cm. In six pigs pyloric motor function was removed by prior pylorectomy. 2. In pylorus-intact animals, isolated pyloric pressure waves (IPPWs) occurred at a median of 2.9 min-1 during duodenal dextrose infusion with the barostat set at or above a threshold of 15 cm. Increases of intragastric pressure above this threshold had no additional effect upon rates of IPPWs. Below this threshold, with identical duodenal dextrose infusion, IPPWs occurred infrequently (0.5 min-1). In pylorus-excised animals virtually no IPPWs were seen. 3. In both pylorus-intact and -excised animals, the rate of antral pressure waves (APWs) was dependent upon intragastric pressure during duodenal infusion of both saline and dextrose. No threshold for stimulation was seen. Duodenal dextrose infusion inhibited APWs in pylorus-intact animals only. 4. With a positive gastroduodenal pressure gradient, gastric emptying was more rapid in pylorus-excised animals than pylorus-intact animals during duodenal dextrose infusion. In contrast, gastric emptying rates were not different between pylorus-intact and -excised animals during saline infusion. 5. These findings suggest an all-or-none-type stimulation of localized pyloric contractions by distension of the stomach beyond a threshold, in synergism with stimulation by nutrients within the upper small bowel. In contrast, stimulation of antral motility is in proportion to distension of the stomach. The pylorus, by way of localized pyloric contractions, is an effective resistor to transpyloric flow in the face of a positive gastroduodenal pressure gradient.

Gastric motor physiology and pathophysiology

The stomach has two distinct physiologic motor areas: the proximal stomach and the distal stomach. The proximal stomach, with its slow, sustained contractions, has a key role in regulating intragastric pressure and gastric emptying of liquids, while the distal stomach, with its peristaltic contractions, has a major role in mixing, trituration, and emptying of solids. Diseases and operations that disturb the motility of these two areas can result in unique adverse motor sequelae. For example, operations that impair proximal gastric motility, such as proximal gastric resection, may cause rapid gastric emptying of liquids and subsequent dumping and diarrhea. In contrast, operations that impair distal gastric contractions, such as truncal vagotomy, may cause slow gastric emptying of solids and chronic gastric atony. Knowledge of the physiology of the stomach in health and of the pathophysiology with disease and after operation provides a basis for the successful treatment and prevention of these disorders.

Relationship between oral glucose tolerance and gastric emptying in normal healthy subjects

The relationships between gastric emptying and intragastric distribution of glucose and oral glucose tolerance were evaluated in 16 healthy volunteers. While sitting in front of a gamma camera the subjects drank 350 ml water containing 75 g glucose and 20 MBq 99mTc-sulphur colloid. Venous blood samples for measurement of plasma glucose, insulin and gastric inhibitory polypeptide were obtained at--2, 2,5,10,15,30,45,60,75,90,105,120 and 150 min. Gastric emptying approximated a linear pattern after a short lag phase (3.3 +/- 0.8 min). The 50% emptying time was inversely related to the proximal stomach 50% emptying time (r = -0.55, p < 0.05) and directly related to the retention in the distal stomach at 120 min (r = 0.72, p < 0.01). Peak plasma glucose was related to the amount emptied at 5 min (r = 0.58, p < 0.05) and the area under the blood glucose curve between 0 and 30 min was related to the amount emptied at 30 min (r = 0.58, p < 0.05). In contrast, plasma glucose at 120 min was inversely related to gastric emptying (r = -0.56, p < 0.05) and plasma insulin at 30 min (r = -0.53, p < 0.05). Plasma insulin at 120 min was inversely related (r = -0.65, p < 0.01) to gastric emptying. The increase in plasma gastric inhibitory polypeptide at 5 min was related directly to gastric emptying (r = 0.53, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Integration of canine proximal gastric, antral, pyloric, and proximal duodenal motility during fasting and after a liquid meal

The aim was to investigate the integration of proximal gastric, antral, pyloric, and duodenal motility during fasting and after feeding. Using a proximal gastric barostat and a manometric assembly with an array of side holes astride the gastroduodenal junction, the gastrointestinal interdigestive migrating motor complex was detected in five of seven conscious fasting dogs. During phase III of the complex, which lasted a mean +/- SEM of 13 +/- 0.5 min, 9.6 +/- 0.9 volume waves were present in the proximal stomach. The volume waves were coordinated with clusters of antral waves 64 +/- 11% of the time and with inhibition of duodenal waves 91 +/- 3% of the time. A 300-ml calorie-dense liquid meal abolished the complex and promptly increased proximal gastric volume in five of six dogs. Volume waves were nearly completely suppressed, while antral waves decreased from 24 +/- 3.0 waves/10 min to 10 +/- 2.8 waves/10 min (P < 0.05) and isolated pyloric pressure waves increased from 7.2 +/- 2.8 waves/10 min to 22 +/- 3.3 waves/10 min (P < 0.005). In summary, proximal gastric motility was integrated with antral, pyloric, and duodenal motility under both fasting and fed conditions. The integrated patterns likely account for the efficient clearance of indigestible solids during fasting and the controlled emptying of nutrients with feeding.

Cholecystokinin octapeptide stimulates phasic and tonic pyloric motility in healthy humans

Stimulation of localised pyloric contractions may be an important mechanism in the slowing of gastric emptying by cholecystokinin infusion. The effect of cholecystokinin octapeptide on fasting pyloric motility was investigated in 14 healthy volunteers. Antral, pyloric, and duodenal pressure responses to normal saline and graded injections of cholecystokinin octapeptide (5, 10, and 20 ng/kg) were measured. Injections were given double blind and in randomised order. All doses of cholecystokinin octapeptide initially stimulated (p < 0.05 cf saline) phasic pressure waves localised to the pylorus--the median number of pyloric pressure waves in the 5 minutes after injection being 0, 3.5, 6, and 7 for the saline and the 5, 10, 20 ng/kg cholecystokinin octapeptide injections respectively. The phasic pyloric motor response to 20 ng/kg cholecystokinin octapeptide injection was greater than that to 5 ng/kg (p < 0.05). Basal pyloric pressure increased after 20 ng/kg (1.0 v 0.2 mm Hg, p < 0.05 cf saline). Antral and duodenal pressure waves were suppressed initially by all doses of cholecystokinin (p < 0.05 cf saline). Subsequently, 20 of the 42 cholecystokinin octapeptide, injections but none of the saline injections, were followed by antropyloric pressure waves. Atropine, 15 micrograms/kg iv as a bolus, and then 4 micrograms/kg/hour iv as an infusion, had no effect on the stimulation of localised phasic pyloric pressure waves by cholecystokinin octapeptide 10 ng/kg. It is concluded that stimulation of pyloric contractions and suppression of antral and proximal duodenal motility may contribute to the slowing of gastric emptying produced by cholecystokinin.

Adaptive changes in the pyloric motor response to intraduodenal dextrose in normal subjects

Gastric emptying of glucose is faster after dietary supplementation of glucose, suggesting specific adaptation to changes in nutrient intake. In the present study, the effects of a continuous long-term (0-120-minute) and two short-term (0-20- and 80-100-minute) intraduodenal infusions of dextrose (2.4 kcal/min) on antropyloroduodenal motility and blood glucose, plasma gastric inhibitory polypeptide, and insulin concentrations were evaluated in nine volunteers. In four volunteers, an intraduodenal infusion of triglyceride (2.4 kcal/min) was administered immediately after the long-term dextrose infusion. The long-term dextrose infusion initially increased isolated pyloric pressure waves (IPPWs) and basal pyloric pressure (P < 0.05 for both), but after about 30 minutes IPPWs and basal pyloric pressure decreased and returned to baseline within 80 minutes. Each short-term infusion increased IPPWs and basal pyloric pressure (P < 0.05 for both). Antral pressure waves remained suppressed during the long-term dextrose infusion. Intraduodenal triglyceride increased IPPWs and basal pyloric pressure (P < 0.05 for both). The long-term dextrose infusion was associated with a sustained increase, and both short-term dextrose infusions were associated with peaks in glucose, insulin, and gastric inhibitory polypeptide levels. There was no significant relationship between biochemical measurements and antropyloroduodenal motility. It is concluded that specific adaptive changes occur rapidly in the phasic and tonic pyloric motor response, but not the antral motor response, to intraduodenal dextrose.

Stimulation of pyloric contractions by intraduodenal triglyceride is persistent and sensitive to atropine

Intraduodenal lipid infusion stimulates phasic and tonic pyloric contractions and suppresses antral contractions. This study determined: (i) whether this response is sustained over 90 min; and (ii) the role of muscarinic mediation of this response. Antropyloroduodenal motility was recorded in 17 healthy volunteers with a sleeve/sidehole manometric assembly. Subjects received either a 90 min intraduodenal infusion of saline or triglyceride (20% Intralipid) at a rate of 1 mL/min; 30 min after the start of this infusion, the eight subjects who received triglyceride were given intravenous atropine 15 micrograms/kg over 30 s, followed by a maintenance infusion of 4 micrograms/kg/h until the study was completed. Intraduodenal triglyceride infusion stimulated isolated pyloric pressure waves consistently, producing a median rate of 2.4 per min after 30 min of triglyceride infusion, compared with a median rate of 0 per min pre-infusion. In intravenous saline studies, there was a reduction (P < 0.05) in the median rate of isolated pyloric pressure waves to 1.3 per min at 90 min, when compared with pyloric pressure waves at 30 min. Atropine reduced isolated pyloric pressure waves to a median rate of 0 per min, significantly different from preatropine (P < 0.01) and from intravenous saline studies (P < 0.0001). These results indicate that the phasic pyloric response to intraduodenal lipid persists during 90 min stimulation, albeit with significant attenuation. In humans, muscarinic cholinergic blockade prevents the occurrence of triglyceride stimulated localized pyloric contractions.

Antroduodenal motility and movements of luminal contents studied by duplex sonography

The motility of the gastroduodenal wall, movement of gastric contents, and velocity curves of transpyloric flow can be synchronously visualized by duplex sonography. In eight healthy individuals, 18 +/- 6 (mean +/- SD) peristaltic cycles per person in response to the ingestion of 500 mL of meat soup were recorded. Coordinated antroduodenal contractions were seen in 67% of the cycles. Two types of duodenogastric reflux were observed. One type occurred in the middle of the peristaltic cycle (midcycle reflux), whereas the other followed immediately after antegrade flow at the end of the cycle (end-cycle reflux). End-cycle reflux was significantly more frequent in conjunction with coordinated (70%) than with uncoordinated (17%) antroduodenal contractions (P less than 0.005). Thus, in the fed state, a short gush of duodenogastric reflux normally precedes the peristaltic closure of the pylorus.

[Electrochemical measuring system for the registration of transmucosal gastrointestinal potential differences]

An electrochemical measuring system for the recording of transmucosal gastrointestinal potential differences based on silver electrodes with double-junctions and continuous-flow saline bridges is described. Under bioelectrochemical control, a probe can passed from the esophagus via the stomach into the duodenum can be accurately assigned to each of these three segments of the intestine. Measurements are demonstrated and applications discussed.

Role of the proximal and distal stomach in mixed solid and liquid meal emptying

The role of the proximal and distal stomach in the emptying of solids and liquids from the stomach remains unclear. We have used a dual isotope technique to quantify proximal and distal stomach emptying of a solid (100 g of 99mTc labelled liver/ground beef) liquid (either 200 ml of normal saline (eight subjects) or 25% dextrose (seven subjects) labelled with 113mIn-diethylenetriaminepenta-acetic acid) mixed meal. A manometric catheter simultaneously measured antral, pyloric, and duodenal motor activity. The liquid component dispersed rapidly throughout the stomach and emptied after a minimal lag period. The emptying of the 25% dextrose was delayed compared with the saline. This delay was associated with increased retention of the liquid in the distal stomach, a significant increase in localised phasic pyloric contractions, and a suppression of antral contractions. The solid component initially resided wholly within a proximal stomach reservoir area. Solids then redistributed from proximal to distal stomach during the emptying of liquid from the stomach. Dextrose delayed gastric emptying of solids compared with saline by increasing the solid lag period and retention in the proximal stomach. There was no significant difference between saline and dextrose meals in the distal stomach retention of solid or in the linear rate of emptying after the lag period. We conclude that, contrary to general opinion, the proximal stomach plays an important role in the control of gastric emptying of solids while the distal stomach is important in the emptying of nutrient liquids.

Hyperglycaemia stimulates pyloric motility in normal subjects

The motor correlates of the delay in gastric emptying produced by hyperglycaemia were investigated in 11 healthy volunteers. Fasting gastroduodenal motility was measured during euglycaemia (blood glucose concentration 3-5 mmol/l) and during hyperglycaemia induced by intravenous dextrose (blood glucose concentration 12-16 mmol/l). Antral, pyloric, and proximal duodenal pressures were recorded by a sleeve/sidehole manometric assembly positioned across the pylorus, with the aid of measurements of transmucosal potential difference. During hyperglycaemia there was stimulation of isolated pyloric pressure waves when compared with the euglycaemia period (p less than 0.05). This was associated with inhibition of antral pressure waves (p less than 0.05). In nine of the 11 subjects an episode of duodenal 'phase III like' activity occurred within 15 minutes of the onset of hyperglycaemia. It is proposed that the stimulation of localised pyloric contractions and inhibition of antral contractions contribute to the delayed gastric emptying induced by hyperglycaemia. Abnormal gastric motility in patients with diabetes mellitus may be the result of hyperglycaemia itself, rather than irreversible autonomic neuropathy.

Cigarette smoking and rate of gastric emptying: effect on alcohol absorption

OBJECTIVE

To examine the effects of cigarette smoking on alcohol absorption and gastric emptying.

DESIGN

Randomised crossover study.

SETTING

Research project in departments of medicine and nuclear medicine.

SUBJECTS

Eight healthy volunteers aged 19-43 who regularly smoked 20-35 cigarettes a day and drank small amounts of alcohol on social occasions.

INTERVENTIONS

Subjects drank 400 ml of a radiolabelled nutrient test meal containing alcohol (0.5 g/kg), then had their rates of gastric emptying measured. Test were carried out (a) with the subjects smoking four cigarettes an hour and (b) with the subjects not smoking, having abstained for seven days or more. The order of the tests was randomised and the tests were conducted two weeks apart.

MAIN OUTCOME MEASURES

Peak blood alcohol concentrations, absorption of alcohol at 30 minutes, amount of test meal emptied from the stomach at 30 minutes, and times taken for 50% of the meal to leave the proximal stomach and total stomach.

RESULTS

Smoking was associated with reductions in (a) peak blood alcohol concentrations (median values in non-smoking versus smoking periods 13.5 (range 8.7-22.6) mmol/l v 11.1 (4.3-13.5) mmol/l), (b) area under the blood alcohol concentration-time curve at 30 minutes (264 x 10(3) (0-509 x 10(3)) mmol/l/min v 140 x 10(3)) (0-217 x 10(3) mmol/l/min), and (c) amount of test meal emptied from the stomach at 30 minutes (39% (5-86%) v 23% (0-35%)). In addition, smoking slowed both the 50% gastric emptying time (37 (9-83) minutes v 56 (40-280) minutes) and the intragastric distribution of the meal. There was a close correlation between the amount of test meal emptied from the stomach at 30 minutes and the area under the blood alcohol concentration-time curve at 30 minutes (r = 0.91; p less than 0.0001).

CONCLUSION

Cigarette smoking slows gastric emptying and as a consequence delays alcohol absorption.

The effect of naloxone on lipid-induced pyloric motor response in humans

This study examines whether opioid receptors are involved in the mediation of the pyloric motor response to intraduodenal lipid infusion. Antral, pyloric, and duodenal manometry was performed in seven healthy volunteers with a sleeve/multiple side-hole manometric assembly. Triglyceride emulsion and normal saline were infused alternately into the duodenum through the manometric assembly for two 30-minute periods each. Naloxone was then administered as an IV bolus, 40 micrograms/kg, followed by an infusion of 60 micrograms.kg-1.h-1 that was continued during testing of the duodenal infusates. Before naloxone administration, intraduodenal lipid produced significant increases in the rate of isolated pyloric pressure waves and basal pyloric tone when compared with saline (P = 0.009 and 0.027, respectively). The pyloric motor responses were unchanged after administration of naloxone, indicating that in humans, naloxone-sensitive opioid mechanisms are not involved in the mediation of lipid-induced pyloric motor responses.

Gastroduodenal motility during the delayed gastric emptying induced by cold stress

We have assessed the changes in gastroduodenal motility responsible for the delay in gastric emptying produced by cold stress. Antropyloroduodenal pressures were recorded in 7 healthy volunteers, concurrent with scintigraphic measurement of gastric emptying. The manometric assembly incorporated a sleeve sensor located across the pylorus and side holes in the antrum and the duodenum. When approximately 25% of a 100-g 99m Tc-labeled ground beef burger had emptied from the stomach, a standardized cold pressor test was applied. This consisted of 60-s immersions of the left hand in iced water (4 degrees C), with 15-s rest periods between immersions, for up to 20 min. Cold stress was associated with slowed emptying from the total stomach (median, 17% before stress vs. 2% during stress; p less than 0.01) and the proximal stomach (9% before vs. 3% during; p less than 0.01). Retrograde movement of the solid meal from the distal to the proximal stomach was observed in 4 subjects. Cold stress increased the number of isolated pyloric pressure waves (p less than 0.05), and decreased the number of antral (p less than 0.01) and propagated antropyloroduodenal pressure waves (p less than 0.05). Phase 3-like duodenal activity occurred in 2 subjects during the first 5 min of stress; otherwise there was a reduction in the number of duodenal pressure waves during stress (p less than 0.05). Basal pyloric pressure was not elevate before, during, or after stress. We conclude that in addition to the previously reported antral inhibition, cold stress is associated with changes in pyloric and duodenal motility and, in some subjects, in the intragastric distribution of food. These modifications in gastroduodenal motility are likely to contribute to the delay in gastric emptying produced by this stimulus.

Pyloric motor function during emptying of a liquid meal from the stomach in the conscious pig

1. In six conscious pigs antral, pyloric and duodenal pressures were recorded with a 5.5 cm sleeve sensor and multiple perfused side holes. The manometric assembly was positioned by dual point transmucosal potential difference measurement. Gastric emptying was measured by drainage of the proximal duodenum through a Thomas cannula. Pressures were correlated with emptying of ingested radiolabelled 5% dextrose. Alteration of emptying was produced by infusion into the more distal duodenum of nutrient and non-nutrient solutions of differing osmolalities. 2. Motor activity of the pylorus and antrum was stimulated by ingestion and modulated by intraduodenal infusion. Duodenal infusion of normal saline was associated with antro-pyloric pressure waves and rapid emptying of the ingested liquid. Duodenal infusion of dextrose, fatty acid, amino acids and hyperosmolar saline was associated with stimulation of isolated pyloric pressure waves, suppression of antral pressure waves and slowing of gastric emptying. 3. The dose-response relationship of these effects was investigated using varying rates of intraduodenal dextrose infusions. The emptying rate of the ingested liquid was inversely related to the rates of delivery of dextrose to the duodenum, directly related to the rate of antro-pyloric pressure waves and inversely related to the rate of isolated pyloric pressure waves. 4. Clearly defined episodes of pulsatile flow produced slightly more than half of the total emptying that occurred. This pulsatile flow was intimately associated in time with antro-pyloric pressure waves. Sequences of isolated pyloric pressure waves were associated with near cessation of emptying. When there were periods of absent pyloric antral pressure waves, flow rates intermediate between the rapid emptying of pulsatile flow during antro-pyloric pressure waves and the near cessation of flow during isolated pyloric pressure waves occurred. 5. The findings suggest a major role for the pylorus in the control of emptying of liquids from the stomach, both as a component of an antro-pyloric peristaltic pump and as a resistor to transpyloric flow during nutrient and hyperosmolar stimulation of duodenal receptors.

The effect of terminal ileal triglyceride infusion on gastroduodenal motility and the intragastric distribution of a solid meal

The infusion of triglyceride emulsions into the terminal ileum in concentrations that approximate those found in malabsorption results in the slowing of gastric emptying. The aim of this study was to characterize the changes in gastroduodenal motility responsible for this effect. Antropyloroduodenal pressures in 8 healthy volunteers were recorded with a manometric assembly incorporating a sleeve sensor across the pylorus and side holes in the antrum and duodenum. Each subject ingested a 100-g, 99m Tc-labeled solid meal; when approximately 25% of the meal had emptied from the stomach, a triglyceride emulsion (20% Intralipid) was infused into the terminal ileum at 1 ml/min for 45 min. Gastric emptying slowed markedly 15-30 min after the start of the lipid infusion (p = 0.01), and there was retrograde movement of the solid meal from the distal to the proximal portion of the stomach. During lipid infusion, there was a decrease in antral (p = 0.01), duodenal (p less than 0.05), and propagated antropyloroduodenal pressure waves (p less than 0.05) and an increase in isolated pyloric pressure waves (p less than 0.05). The rate of gastric emptying correlated with antral pressure waves (r = 0.92, p less than 0.001), duodenal pressure waves (r = 0.80, p less than 0.01), and propagated pressure waves (r = 0.88, p = 0.0025) and correlated inversely with the number of isolated pyloric pressure waves (r = -0.60, p = 0.05). The changes in antral, pyloric, and duodenal motility and the intragastric redistribution of a solid meal associated with ileal lipid infusion are likely to contribute to the delay in gastric emptying caused by this stimulus.

Motor mechanisms associated with slowing of the gastric emptying of a solid meal by an intraduodenal lipid infusion

The aim of this study was to define better the motor phenomena associated with the slowing of gastric emptying by a duodenal lipid infusion. Antral, pyloric and duodenal motility were recorded in 10 healthy subjects with a manometric assembly which incorporated multiple perfused side-holes and a sleeve sensor positioned astride the pylorus. The gastric emptying of a standard solid meal and the distribution of the ingesta between the proximal and distal stomach were monitored with a radionuclide technique. A triglyceride emulsion was infused into the duodenum for 45 min once 25% of the meal had emptied. The infusion caused significant slowing in the rate of gastric emptying (P less than 0.01). This slowing in gastric emptying was associated with the suppression of pressure waves in the distal antrum (P less than 0.01) and proximal duodenum (P less than 0.01), the induction of pressure waves isolated to a narrow pyloric segment (P less than 0.01), and a redistribution of ingesta from the distal to proximal stomach. These findings suggest that pressure waves isolated to the pylorus, changes in the intragastric distribution of ingested food, and changes in proximal duodenal motility may all act in concert with changes in antral motility to regulate the gastric emptying of solids.

Pyloric motor response to intraduodenal dextrose involves muscarinic mechanisms

The delivery of dextrose solutions to the duodenum is associated with the stimulation of phasic and tonic pyloric contraction. In this study, the effects of intravenous atropine on the antropyloroduodenal motor responses to intraduodenal infusions of 25% dextrose were assessed in 10 normal volunteers. Antropyloroduodenal pressures were recorded with a manometric assembly incorporating a sleeve sensor spanning the pylorus, and sideholes in the antrum and duodenum. In each experiment, three intraduodenal infusions of 25% dextrose were given at a rate of 4 ml/min, for a median duration of 19 min (range 17-20). During the second dextrose infusion, intravenous atropine was given as a bolus (15 micrograms/kg) followed by an infusion (4 micrograms/kg.min), which was continued until the end of each experiment. Before atropine was given, the pyloric motor response to the second dextrose infusion was not significantly different from the response to the first infusion, but after administration of atropine there was a rapid decrease in the rate of isolated pyloric pressure waves, from 0.8 to 0.1 per minute (p less than 0.05). The isolated pyloric pressure wave response to the third dextrose infusion was completely blocked, and there was a much smaller maximum increase in basal pyloric pressure compared with the first infusion (p less than 0.01). This study indicates that intraduodenal dextrose reproducibly stimulates isolated pyloric pressure waves and increases basal pyloric pressure by mechanisms that involve muscarinic receptors.