Peripheral pacemakers and patterns of slow wave propagation in the canine small intestine in vivo

In an anesthetized, open-abdomen, canine model, the propagation pattern of the slow wave and its direction, velocity, amplitude, and frequency were investigated in the small intestine of 8 dogs. Electrical recordings were made using a 240-electrode array from 5 different sites, spanning the length of the small intestine. The majority of slow waves propagated uniformly and aborally (84%). In several cases, however, other patterns were found including propagation in the oral direction (11%) and propagation block (2%). In addition, in 69 cases (3%), a slow wave was initiated at a local site beneath the electrode array. Such peripheral pacemakers were found throughout the entire intestine. The frequency, velocity, and amplitude of slow waves were highest in the duodenum and gradually declined along the intestine reaching lowest values in the distal ileum (from 17.4+/-1.7 c/min to 12.2+/-0.7 c/min; 10.5+/-2.4 cm/s to 0.8+/-0.2 cm/s, and 1.20+/-0.35 mV to 0.31+/-0.10 mV, respectively; all p<0.001). Consequently, the wavelength of the slow wave was strongly reduced from 36.4+/-0.8 cm to 3.7 +/- 0.1 cm (p<0.001). We conclude that the patterns of slow wave propagation are usually, though not always, uniform in the canine small intestine and that the gradient in the wavelength will influence the patterns of local contractions.     

Immunocytochemical localization of ornithine transcarbamylase in rat intestinal mucosa. Light and electron microscopic study

We investigated light and electron microscopic localization of ornithine transcarbamylase (OTC) in rat intestinal mucosa. In the immunoblotting assay of OTC-related protein, a single protein band with a molecular weight of about 36,500 is observed in extracts of liver and small intestinal mucosa but is not observed in those of stomach and large intestine. For light microscopy, tissue slices of the digestive system were embedded in Epon and stained by using anti-bovine OTC rabbit IgG and the immunoenzyme technique. For electron microscopy, slices of these and the liver tissues were embedded in Lowicryl K4M and stained by the protein A-gold technique. By light microscopy, the absorptive epithelial cells of duodenum, jejunum, and ileum stained positively for OTC, but stomach, large intestine, rectum, and propria mucosa of small intestine were not stained. Electron microscopy showed that gold particles representing the antigenic sites for OTC were confined to the mitochondrial matrix of hepatocytes and small intestinal epithelial cells. However, the enzyme was detected in mitochondria of neither liver endothelial cells, submucosal cells of small intestine, nor large intestinal epithelial cells. Labeling density of mitochondria in the absorptive epithelial cells of duodenum, jejunum, and ileum was about half of that in liver cells.     

Longitudinal and circumferential spike patches in the canine small intestine in vivo

In an open-abdominal anesthetized and fasted canine model of the intact small intestine, the presence, location, shape, and frequency of spike patches were investigated. Recordings were performed with a 240-electrode array (24 x 10, 2-mm interelectrode distance) from several sites sequentially, spanning the whole length of the small intestine. All 240 electrograms were recorded simultaneously during periods of 5 min and were analyzed to reconstruct the origin and propagation of individual spikes. At every level in the small intestine, spikes propagated in all directions before stopping abruptly, thereby activating a circumscribed area termed a "patch." Two types of spikes were found: longitudinal spikes, which propagated predominantly in the longitudinal direction and occurred most often in the duodenum, and a second type, circumferential spikes, which propagated predominantly in the circular direction and occurred much more frequently in the jejunum and ileum. Circumferential spikes conducted faster than longitudinal spikes (17 +/- 6 and 7 +/- 2 cm/s, respectively; P < 0.001). Circumferential spikes originated in >90% of all cases from the antimesenteric border, whereas longitudinal spikes were initiated all around the circumference of the intestinal tube. Finally, the spatial sequence of spike patches after the slow wave was very irregular in the upper part of the intestine but much more regular in the lower part. In conclusion, spikes and spike patches occur throughout the small intestine, whereas their type, sites of origin, extent of propagation, and frequencies of occurrence differ along the length of the small intestine, suggesting differences in local patterns of motility.     

Mesenteric Lymphoblast Localization Throughout the Murine Small Intestine: Temporal Analysis Relating Intestinal Length and Lymphoblast Division

Abstract. Mesenteric lymphoblasts (MLN) have a predilection to selectively localize in the lamina propria and epithelium of the small intestine. Using an adoptive transfer method, we examined the localization kinetics of these blasts in the intestinal wall with respect to their distribution from duodenum to terminal ileum and also assessed their mitotic activity by autoradiographic techniques. ³H-thymidine-labelled MLN cells were found throughout the small intestine by 6 hr post-transfer and reached a maximum frequency in this organ by 24 hr post-transfer.
Donor blasts were most frequent in the duodenum and terminal ileum regions of the gut. Subsequently, the frequency of labelled cells throughout the intestinal wall declined to near zero. the apparent accumulation of MLN blasts in the gut was not related to either a temporary retention and departure from the pulmonary vasculature or to mitotic division of labelled cells in the gut wall. A model describing the relationship between MLN blast localization kinetics in various segments of the intestine was formulated.     

Mesenteric lymphoblast localization throughout the murine small intestine: temporal analysis relating intestinal length and lymphoblast division

Mesenteric lymphoblasts (MLN) have a predilection to selectively localize in the lamina propria and epithelium of the small intestine. Using an adoptive transfer method, we examined the localization kinetics of these blasts in the intestinal wall with respect to their distribution from duodenum to terminal ileum and also assessed their mitotic activity by autoradiographic techniques. 3H-thymidine-labelled MLN cells were found throughout the small intestine by 6 hr post-transfer and reached a maximum frequency in this organ by 24 hr post-transfer. Donor blasts were most frequent in the duodenum and terminal ileum regions of the gut. Subsequently, the frequency of labelled cells throughout the intestinal wall declined to near zero. The apparent accumulation of MLN blasts in the gut was not related to either a temporary retention and departure from the pulmonary vasculature or to mitotic division of labelled cells in the gut wall. A model describing the relationship between MLN blast localization kinetics in various segments of the intestine was formulated.     

The myogenic component in distention-induced peristalsis in the guinea pig small intestine

In an in vitro model for distention-induced peristalsis in the guinea pig small intestine, the electrical activity, intraluminal pressure, and outflow of contents were studied simultaneously to search for evidence of myogenic control activity. Intraluminal distention induced periods of nifedipine-sensitive slow wave activity with superimposed action potentials, alternating with periods of quiescence. Slow waves and associated high intraluminal pressure transients propagated aborally, causing outflow of content. In the proximal small intestine, a frequency gradient of distention-induced slow waves was observed, with a frequency of 19 cycles/min in the first 1 cm and 11 cycles/min 10 cm distally. Intracellular recording revealed that the guinea pig small intestinal musculature, in response to carbachol, generated slow waves with superimposed action potentials, both sensitive to nifedipine. These slow waves also exhibited a frequency gradient. In addition, distention and cholinergic stimulation induced high-frequency membrane potential oscillations (~55 cycles/min) that were not associated with distention-induced peristalsis. Continuous distention produced excitation of the musculature, in part neurally mediated, that resulted in periodic occurrence of bursts of distally propagating nifedipine-sensitive slow waves with superimposed action potentials associated with propagating intraluminal pressure waves that caused pulsatile outflow of content at the slow wave frequency.     

Functional reentry and circus movement arrhythmias in the small intestine of normal and diabetic rats

In a few recent studies, the presence of arrhythmias based on reentry and circus movement of the slow wave have been shown to occur in normal and diseased stomachs. To date, however, reentry has not been demonstrated before in any other part of the gastrointestinal system. No animals had to be killed for this study. Use was made of materials obtained during the course of another study in which 11 rats were treated with streptozotocin and housed with age-matched controls. After 3 and 7 mo, segments of duodenum, jejunum, and ileum were isolated and positioned in a tissue bath. Slow wave propagation was recorded with 121 extracellular electrodes. After the experiment, the propagation of the slow waves was reconstructed. In 10 of a total of 66 intestinal segments (15%), a circus movement of the slow wave was detected. These reentries were seen in control (n = 2) as well as in 3-mo (n = 2) and 7-mo (n = 6) diabetic rats. Local conduction velocities and beat-to-beat intervals during the reentries were measured (0.42 ± 0.15 and 3.03 ± 0.67 cm/s, respectively) leading to a wavelength of 1.3 ± 0.5 cm and a circuit diameter of 4.1 ± 1.5 mm. This is the first demonstration of a reentrant arrhythmia in the small intestine of control and diabetic rats. Calculations of the size of the circuits indicate that they are small enough to fit inside the intestinal wall. Extrapolation based on measured velocities and rates indicate that reentrant arrhythmias are also possible in the distal small intestine of larger animals including humans.     

Relationship between the degree of the small intestine motility and the activity of hexokinase in its smooth muscle layer

Interrelationship between the motility of the small intestine and the intensity of energy formation in its smooth muscle layer was studied. The hexokinase activity was found to be significantly higher in the muscle layer of the duodenum as compared to that activity in the ileum and jejunum. No statistically significant differences in the hexokinase activity were revealed between the ileum and jejunum. The results obtained showed hexokinase activity to be highly variable, these values directly correlating with the motor activity of the intestinal muscle layer, representing the contractile apparatus of the intestine.     

In vivo changes in the intestinal reflexes and the response to CCK in the inflamed small intestine of the rat

Functional motor changes and morphological alterations have been associated with intestinal inflammation. The aim of our study was to evaluate functional alterations of intestinal reflexes and of the responses to CCK in the Trichinella spiralis model of intestinal inflammation. Rats were prepared with strain gauges and electrodes in the small intestine to evaluate spontaneous motor activity, the ascending contraction of the peristaltic reflex, and the motor responses to CCK-8 infusion. Infected animals showed increased motor activity at the duodenum and jejunum but not at the ileum. Ascending contraction was increased in both duodenum and ileum. Ascending excitation after N(omega)-nitro-L-arginine was still increased as well as the residual response after atropine. Response to CCK-8 during intestinal inflammation was changed in the jejunum, in which it turned from the inhibition shown in healthy animals to excitation. NADPH-diaphorase staining did not show any changes between distribution and density of positive neurons in either healthy or infected animals. In conclusion, intestinal inflammation induces functional changes in the motor activity that could explain the abnormal motor responses observed in inflammatory disorders.     

Similarities and differences in the propagation of slow waves and peristaltic waves

The relationship between slow waves and peristaltic reflexes has not been well analyzed. In this study, we have recorded the electrical activity of slow waves together with that generated by spontaneous peristaltic contractions at 240 extracellular sites simultaneously. Recordings were made from five isolated tubular and six sheet segments of feline duodenum superfused in vitro. In all preparations, slow waves propagated as broad wave fronts along the longitudinal axis of the preparation in either the aborad or the orad direction. Electrical potentials recorded during peristalsis (peristaltic waves) also propagated as broad wave fronts in either directions. Peristaltic waves often spontaneously stopped conducting (46%), in contrast to slow waves that never did. Peristaltic waves propagated at a lower velocity than the slow waves (0.98 +/- 0.25 and 1.29 +/- 0.28 cm/s, respectively; P < 0.001; n = 24) and in a direction independent of the preceding slow wave direction (64% in the same direction, 46% in the opposite direction). In conclusion, slow waves and peristaltic waves in the isolated feline duodenum seem to constitute two separate electrical events that may drive two different mechanisms of contraction in the small intestine.     

Transport of putrescine across duodenal,jejunal and ileal brush-border membrane of chicks (Gallus domesticus)

Luminal polyamines and their absorption are essential for proliferation of the enterocytes and, therefore, nutrition, health and development of the animal. The transport systems that facilitate the uptake of putrescine were characterized in chick duodenal, jejunal and ileal brush-border membrane vesicles prepared by MgCl2 precipitation from three-week-old chicks. An inwardly-directed Na+ gradient did not stimulate putrescine uptake and, therefore, putrescine transport in chick intestine. In the duodenum, jejunum and ileum, kinetics of putrescine transport fitted a model with a single affinity component plus a non-saturable component. The affinity (Kt) for [3H]putrescine transport across the brush-border membrane increased along the length of the small intestine. A model of intermediate affinity converged to the data obtained for [3H]putrescine transport with Kt approximating 1.07 and 1.05 mM or duodenum and jejunum, respectively; and high affinity with a Kt of 0.35 mM for the ileum. The polyamines cadaverine, putrescine, spermidine and spermine strongly inhibited the uptake of [3H]putrescine into chick brush-border membrane vesicles, more so for the jejunum and ileum than the duodenum. The kinetics of cadaverine, spermidine and spermine inhibition are suggestive of competitive inhibition of putrescine transport. These uptake data indicate that a single-affinity system facilitates the intestinal transport of putrescine in the chick; and the affinity of transporter for putrescine is higher in the ileum than in the proximal sections of the small intestine. In addition, this study shows that the ileum of chicks plays an important role in regulating cellular putrescine concentration.     

Post-Mortem Autodigestion of the Intestinal Mucosa of the Turkey

A gradient of post-mortem activity exists in the small intestine of the turkey. It is manifested by immediate disturbance of intestinal epithelium of the duodenum, a somewhat similar but lessened effect in the jejunum, and a long delayed action in the ileum. The recognition of such a gradient stresses the rapidity with which one must proceed in handling such tissues for technical studies. In preparing intestinal tissues for histological examination, the duodenum and jejunum must be removed immediately after killing the specimen, opened, washed carefully with warm saline to eliminate excess debris, ferments and mucous, and fixed forthwith.     

Iron absorption by small intestine of chickens

Iron (Fe) absorption by three segments (duodenum, jejunum, and ileum) of the small intestine of chickens was studied by a perfusion technique in vivo in closed circuit using⁵⁹Fe Cl₃ and was related to the histological characteristics of each segment. The serosal transfers of Fe for the duodenum and jejunum were the same (14%/cm), but significantly different (p<0.05) from those of the ileum (9%/cm), which may be explained by the morphological and histological properties of the gut of chickens. However, the presence of Fe in blood and in liver was significantly lower after perfusion of the jejunum and ileum than after perfusion of the duodenum. It is concluded that chickens show an early adaptation of small intestine to Fe absorption in response to the considerable loss of Fe suffered during the laying process.     

The effect of food protein-induced intestinal anaphylaxis on rate of transit

The aim of this study was to determine if the altered jejunal motility previously demonstrated in this animal model of food protein-induced intestinal anaphylaxis is (a) a localized (the jejunal site of challenge), or a generalized response of the small intestine, and (b) associated with more rapid aboral transit of intraluminal contents. Hooded-Lister rats, 100-150 g in weight, were sensitized by intraperitoneal injection of 10 micrograms egg albumin. Control rats were sham-sensitized. On day 7 rats were surgically prepared with six bipolar electrodes from duodenum to ileum and (or) a jejunostomy tube was positioned at the ligament of Treitz. On day 14, after an 18-h fast, recording of myoelectric activity were obtained from four sensitized animals with electrodes from duodenum to ileum during a control period for 45 min after saline challenge and for 45 min after antigen challenge. Control (n = 25) and sensitized (n = 31) animals with only a jejunostomy had Na2 51CrO4 instilled through the jejunostomy in 0.5 mL of saline, with or without egg albumin, either during a fast or after a standard meal. Propulsion of isotope through the small bowel was allowed to progress for 15 min, the animals were sacrificed, and their gut was removed for division into eight equal segments of small intestine, cecum, and remaining colon. The radioactivity of each segment was determined in a gamma counter.(ABSTRACT TRUNCATED AT 250 WORDS)     

Seasonal variation in gastric myoelectrical activity in young Japanese females

In order to test our hypothesis that there is seasonal variation in digestion and absorption of dietary carbohydrate from the intestine, we previously determined the amount of unabsorbed carbohydrate after breakfast by the breath hydrogen test in the four seasons. In pursuing our hypothesis further, we also recorded gastric myoelectrical activity before and after the breakfasts. In the current report, we describe the seasonality of gastric myoelectrical activity. Twenty-six Japanese female subjects were studied in winter, spring, summer and autumn. The cutaneous electrogastrogram was analysed by spectral analysis to compute the pre- and post-prandial dominant slow wave frequency (DF), and percentage of the 2 - 4 cpm gastric slow wave (Normal %). Two-factor ANOVA indicated that there was no significant seasonal variation in DF and Normal %. These results indicate that seasonal variations in digestion and absorption of dietary carbohydrate are caused by factors other than gastric and small intestinal motility.     

Distribution and subcellular localization of acylpeptide hydrolase and acylase I along the hog gastro-intestinal tract

The distribution of acylase I and acylpeptide hydrolase along the hog small intestine was investigated. No significant changes in their respective specific activity was found when the intestine was cut off and divided into eight segments (taken every 200 cm) so as to specifically study the duodenum, jejunum and ileum. Upon performing subcellular fractionation of hog enterocytes, it was observed that acylpeptide hydrolase is a soluble enzyme, while acylase I is essentially a soluble protein accounting for only 5% of the activity associated with the whole membrane fraction. The membrane-bound acylase I was neither solubilized by phosphatidylinositol-specific phospholipase C from Bacillus cereus nor by detergents which are commonly used to solubilize alkaline phosphatase, a glycosylphosphatidylinositol-anchored protein. When a phase separation was carried out in Triton X-114, all the anchored-membrane proteins of the intestinal membranes were located in the detergent-rich phase, while acylase I was present in the detergent-poor phase. Finally, the immunolabeling of intestinal cells with specific antibodies definitively established the cytoplasmic localization of acylase I. Acylpeptide hydrolase and acylase I therefore both are located in the enterocyte cytoplasm.     

Barrier properties and tight junction protein expression along the longitudinal axis of rat intestine

The tight junction (TJ) protein family of claudins is a major determinant of barrier properties in a wide variety of epithelia. Aim of the study was to compare epithelial barrier properties with the presence of TJ proteins in exactly defined intestinal segments. Transepithelial resistance (R(t)) of duodenum, jejunum, ileum and colon tissue preparations was measured in Ussing chambers. In parallel, expression of TJ proteins was analyzed by Western blots. Colon was characterized by higher R(t) than more proximal segments. However, among the small intestinal segments, R(t) was highest in duodenum and lowest in ileum. Along the intestine different claudins were detected by Western blotting with different signal intensities. Colon showed strongest signals for sealing claudins in accordance with R(t), whereas predominant expression of permeability-mediating claudins was observed in small intestinal segments. Along the intestine, claudins show a marked segment-specific expression which is in accordance with respective barrier properties.     

Influence of age on duodenal brush border membrane and specific activities of brush border membrane enzymes in Wistar rats.

To examine age-related changes in the morphology of intestinal brush border membrane (BBM; microvilli) and specific activities of intestinal BBM enzymes including alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (gamma-GT), and disacchridase, four groups of Wistar rats were sacrificed at 2.5 wk, 5 wk, 5 mon and 23 mon. In an electron microscopic examination, morphologically a less dense BBM structure in the duodenum of rats aged 23 mon was observed than that of rats aged 5 mon. Specific activity of ALP in the duodenum from 5-mon-old rats was significantly higher than from rats aged 2.5 wk and 23 mon. The mucosal tissues from 5-wk-old rats had significantly higher specific activity of gamma-GT than did tissues from the other ages. In sucrase and maltase specific activities, 5-mon-old rats had higher activities of these enzymes than other age groups, especially 2.5-wk- and 23-mon-old rats. There was also a significant effect of site on intestinal BBM enzyme activities in post-weanling rats. Regional gradients of ALP and gamma-GT along the entire small intestine (duodenum > jejunum > ileum) were remarkable. Disaccharidase activities peaked in the jejunum and declined toward both the duodenum and ileum. Taken together the result obtained here suggested that 5-mon-old rats had the most elevated intestinal function. This result also strongly indicated that the structure of the intestinal BBM and development of intestinal BBM enzymes in Wistar rate were markedly influenced by age during the postnatal period.