Gastric myoelectric and motor activity in dogs after isoflurane anesthesia

Gastrointestinal Tracking and Gastric Emptying of Coated Capsules in Rats with or without Sedation Using CT imaging

Following oral administration, gastric emptying is often a rate-limiting step in the absorption of drugs and is dependent on both physiological and pharmaceutical factors. To guide translation into humans, small animal imaging during pre-clinical studies has been increasingly used to localise the gastrointestinal transit of solid dosage forms. In contrast to humans, however, anaesthesia is usually required for effective imaging in animals which may have unintended effects on intestinal physiology. This study evaluated the effect of anaesthesia and capsule size on the gastric emptying rate of coated capsules in rats. Computed tomography (CT) imaging was used to track and locate the capsules through the gastrointestinal tract. Two commercial gelatine mini-capsules (size 9 and 9h) were filled with barium sulphate (contrast agent) and coated using Eudragit L. Under the effect of anaesthesia, none of the capsules emptied from the stomach. In non-anaesthetised rats, most of the size 9 capsules did not empty from the stomach, whereas the majority of the smaller size 9h capsules successfully emptied from the stomach and moved into the intestine. This study demonstrates that even with capsules designed to empty from the stomach in rats, the gastric emptying of such solid oral dosage forms is not guaranteed. In addition, the use of anaesthesia was found to abolish gastric emptying of both capsule sizes. The work herein further highlights the utility of CT imaging for the effective visualisation and location of solid dosage forms in the intestinal tract of rats without the use of anaesthesia.

Enhanced electrogastrography: A realistic way to salvage a promise that was never kept?

AIM

To enhance the clinical utility of electrogastrography (EGG), which has been recorded since 1922, but is clinically unutilized.

METHODS

An innovative method to salvage the promise of EGG is proposed by introducing a preliminary procedure, while maintaining the electrodes, standardized equipment, and signal processing utilized in the well-established EGG testing of today. The proposed enhanced EGG (EEGG) protocol involves swallowing an ingestible capsule containing miniature electronic oscillator embedded in an expandable, self-disintegratable, biocompatible pseudobesoar residing in the stomach for the duration of the test. The benefits of the proposed approach are outlined, tested and discussed in details.

RESULTS

Experiments were performed on eight mongrel dogs (6F, 4M, 23.8 ± 3.3 kg). Four were administered an active EEGG capsule, while the rest were given a deactivated (battery removed) capsule. Pharmacologically facilitated gastric motility revealed a significant (P < 0.01) Pearson correlation between gastric motility indices obtained by force transducers implanted directly on the stomach, and the motility indices obtained by EEGG. A particular emphasis was made on preserving standard EGG-related hardware and software in order to facilitate the introduction of the proposed EEGG in environments which already utilize standard EGG testing. The expanded intragastric pseudobezoar containing the miniature electronic oscillator was retained during the tests, and could be disintegrated on demand.

CONCLUSION

Enhancing standard EGG by an ingestible, self-expanding and self-disintegrating pseudobesoar containing a miniature electronic oscillator can be an important avenue for clinical applicability of this test.

Catheter-based acoustic interrogation device for real-time monitoring of the dynamics of the lower esophageal sphincter: in vitro and pilot canine studies

This paper presents a novel minimally-invasive catheter-based acoustic interrogation device for real-time monitoring the dynamics of the lower esophageal sphincter (LES). Dysfunction of the LES could result gastrointestinal (GI) diseases, such as gastroesophageal reflux disease (GERD). A micro-oscillator actively emitting sound wave at 16 kHz is located at one side of the LES, and a miniature microphone is located at the other side of the LES to capture the sound generated from the oscillator. Thus, the dynamics of the opening and closing of the LES can be monitored. The device was tested in vitro by utilizing a custom-designed LES simulator, as well as in vivo in a pilot canine model. In the in vitro test, the sound was captured by the microphone and its strength was correlated with the level of LES opening and closing which was controlled by the simulator. The measurements showed statistically significant (p  <  0.05) Pearson correlation coefficients (0.905 on the average in quiet environment and 0.736 on the average in noisy environment, DOF  =  9). In the in vivo test, the LES was forced open and closed by a transoral endoscope, which was monitored in real-time by a transpyloric endoscope inserted from the duodenum and positioned into the distal stomach. Frame-by-frame video analysis validated the interrelation between the sound strength and the LES opening and closing. The LES dynamics monitored by the proposed device has the potential to become a valuable minimally-invasive technique for understanding LES dysfunction.

Transcutaneous intraluminal impedance measurement for minimally invasive monitoring of gastric motility: validation in acute canine models

Transcutaneous intraluminal impedance measurement (TIIM) is a new method to cutaneously measure gastric contractions by assessing the attenuation dynamics of a small oscillating voltage emitted by a battery-powered ingestible capsule retained in the stomach. In the present study, we investigated whether TIIM can reliably assess gastric motility in acute canine models. Methods. Eight mongrel dogs were randomly divided into 2 groups: half received an active TIIM pill and half received an identically sized sham capsule. After 24-hour fasting and transoral administration of the pill (active or sham), two force transducers (FT) were sutured onto the antral serosa at laparotomy. After closure, three standard cutaneous electrodes were placed on the abdomen, registering the transluminally emitted voltage. Thirty-minute baseline recordings were followed by pharmacological induction of gastric contractions using neostigmine IV and another 30-minute recording. Normalized one-minute baseline and post-neostigmine gastric motility indices (GMIs) were calculated and Pearson correlation coefficients (PCCs) between cutaneous and FT GMIs were obtained. Statistically significant GMI PCCs were seen in both baseline and post-neostigmine states. There were no significant GMI PCCs in the sham capsule test. Further chronic animal studies of this novel long-term gastric motility measurement technique are needed before testing it on humans.

Real-time gastric motility monitoring using transcutaneous intraluminal impedance measurements (TIIM)

The stomach plays a critical role in digestion, processing ingested food mechanically and breaking it up into particles, which can be effectively and efficiently processed by the intestines. When the motility of the stomach is compromised, digestion is adversely affected. This can lead to a variety of disorders. Current diagnostic techniques for gastric motility disorders are seriously lacking, and are based more on eliminating other possibilities rather than on specific tests. Presently, gastric motility can be assessed by monitoring gastric emptying, food transit, intragastric pressures, etc. The associated tests are usually stationary and of relatively short duration. The present study proposes a new method of measuring gastric motility, utilizing the attenuation of an oscillator-induced electrical signal across the gastric tissue, which is modulated by gastric contractions. The induced high-frequency oscillator signal is generated within the stomach, and is picked up transluminally by cutaneous electrodes positioned on the abdominal area connected to a custom-designed data acquisition instrument. The proposed method was implemented in two different designs: first a transoral catheter was modified to emit the signal inside the stomach; and second, a gastric retentive pill was designed to emit the signal. Both implementations were applied in vivo on two mongrel dogs (25.50 kg and 25.75 kg). Gastric contractions were registered and quantitatively compared to recordings from force transducers sutured onto the serosa of the stomach. Gastric motility indices were calculated for each minute, with transluminal impedance measurements and the measurements from the force transducers showing statistically significant (p < 0.05) Pearson correlation coefficients (0.65 ± 0.08 for the catheter-based design and 0.77 ± 0.03 for the gastric retentive pill design). These results show that transcutaneous intraluminal impedance measurement has the potential with further research and development to become a useful diagnostic technique.

Impaired gastric motor activity after abdominal surgery in rats

Postoperative ileus (POI) is a transient bowel dysmotility that occurs following abdominal surgery. Several mechanisms have been proposed such as neural reflex and inflammatory changes. We focused on gastric motility after abdominal surgery in rats. To investigate the time course of gastric motility after surgery, gastric motility was continuously recorded before, during and after surgery. After laparotomy, terminal ileum was manipulated for 10 min. Gastric motility was recorded by a strain gauge transducer implanted on the serosal surface of the stomach. To investigate whether peripheral sympathetic nerve is involved in the pathogenesis of POI, effects of guanethidine and celiac ganglionectomy were tested on the postoperative gastric motility. Although isoflurane anaesthesia reduced the gastric motility to 40%, the motility recovered immediately when isoflurane was withdrawn. Intestinal manipulation reduced the postoperative gastric motility for 3-24 h after surgery, compared with preoperative levels. Guanethidine administration and celiac ganglionectomy restored the impaired gastric motility. Feeding increased the gastric motility in each group. It is suggested that the pathogenesis of postoperative gastric ileus induced by intestinal manipulation involves viscero-sympathetic pathways. Intestinal manipulation causes impaired gastric motility via inhibitory sympathetic efferent pathway. Feeding may improve the postoperative gastric motility.

Effects of Isoflurane on gastrointestinal motility after brief exposure in rats

In pre-clinical studies, investigation of oral formulations often necessitates the use of general anesthesia to facilitate deposition of material directly into the stomach. Since the effectiveness of intestinal drug absorption is dependent on gastric emptying (GE) and intestinal motility, drugs that influence either will also influence drug absorption. This study investigated gastrointestinal motility in rats after brief exposure to Isoflurane (ISO) general anesthesia for orogastric gavage. The use of metochlopramide was also evaluated. Twenty-five fasted rats were induced with brief ISO anesthesia (<6 min). Rats were gavaged a gelatin capsule (8mm (L) x 2.0mm (o.d.)) containing 9 mg of activated charcoal powder (gastrointestinal marker) and rapidly recovered. Gavage was performed using a 15 cm feeding device with a soft hollow tip to hold the capsule. Study included three groups (60 and 120 min recovery, metochlopramide pre-treatment with 60 min recovery) and control. Animals were sacrificed for exposure and examination of the gastrointestinal tract following the allocated recovery period. Gastrointestinal transit of charcoal was reduced approximately 50% 120 min after brief ISO anesthesia. Metochlopramide pre-treatment did not increase gastrointestinal propulsion despite increased GE. These data warrant consideration in intestinal drug absorption studies where ISO is the anesthetic of choice.

Cerebral 6-[(18)F]fluoro-L-DOPA (FDOPA) metabolism in pig studied by positron emission tomography

We measured 6-[(18)F]fluoro-L-DOPA (FDOPA) uptake and metabolism in the brain of 4-month-old female pigs (n = 8) using a high-resolution positron emission tomograph (PET) in 3D mode. The mean net blood-brain clearance of FDOPA (K(i)(D)) to striatum was 0.011 ml g(-1) min(-1). Correcting for the elimination of decarboxylated metabolites from striatum (k(loss) = 0.004 min(-1)) increased the apparent magnitude of the estimate of K(i)(D) by 50%, at the expense of doubling the variance of the mean estimate. The mean decarboxylation rate of FDOPA in striatum relative to the cerebellum input (k(3)(s)) was 0.008 min(-1). For multicompartmental analyses, the FDOPA partition volume (V(e)(D)) was constrained to the individual value observed in cerebellum (mean = 0.53 ml g(-1)), with correction for the presence in brain of the plasma metabolite 3-O-methyl-FDOPA (OMFD). Using the first 60 min of the dynamic PET scans, the rate constant of FDOPA decarboxylation (k(3)(D)) was estimated to be 0.037 min(-1 )in striatum, but was not significantly different than zero in frontal cortex. Fitting of a compartmental model correcting for elimination of decarboxylated metabolites to the complete PET frame-sequence (120 min) increased the variance of the estimate of k(3)(D) in striatum. The magnitude of k(3)(D) in striatum of young pig was less than values estimated previously in neonatal piglet, adult monkey, and human. MRI-based simulations predicted that recovery of radioactivity from pig striatum was highly sensitive to the volume of interest. We conclude that the spatial resolution of our tomograph reduces the apparent magnitude of k(3)(D) in striatum. However, anaesthetised pigs are an appropriate experimental model for PET studies of DOPA decarboxylation in striatum.