Gastric emptying disorders. Tests and treatments

Kit mutants and gastrointestinal physiology

There has been considerable speculation about the function of interstitial cells of Cajal (ICC) since their discovery more than 100 years ago. It has been difficult to study these cells under native conditions, but great insights about the function of ICC have come from studies of genetic models with loss-of function mutations in the Kit signalling pathway. First it was discovered that signalling via Kit (a receptor tyrosine kinase) was vital for the development and maintenance of the ICC phenotype in gastrointestinal (GI) muscles. In compound heterozygotes (W/W(V) and Sl/Sl(d) animals), where there are partial loss-of-function mutations in Kit receptors or Kit ligand (stem cell factor), ICC failed to develop in various regions of the GI tract, but no major changes in the smooth muscle layers or enteric nervous system occurred in the absence of these cells. Animals with these mutations provided an unprecedented opportunity to understand the role of ICC in GI motor function, and it is now clear from these studies that ICC serve as: (i) pacemaker cells, generating the spontaneous electrical rhythms of the gut known as slow waves; (ii) a propagation pathway for slow waves so that large areas of the musculature can be entrained to a dominant pacemaker frequency; (iii) mediators of excitatory cholinergic and inhibitory nitrergic neural inputs from the enteric nervous system, and (iv) stretch receptors that modulate membrane potential and electrical slow wave frequency. This review describes the use of genetic models to understand the important physiological role of ICC in the GI tract.

Pacing of interstitial cells of Cajal in the murine gastric antrum: neurally mediated and direct stimulation

Phase advancement of electrical slow waves and regulation of pacemaker frequency was investigated in the circular muscle layer of the gastric antra of wild-type and W/W(V) mice. Slow waves in the murine antrum of wild-type animals had an intrinsic frequency of 4.4 cycles min(-1) and were phase advanced and entrained to a maximum of 6.3 cycles min(-1) using 0.1 ms pulses of electrical field stimulation (EFS) (three pulses delivered at 3-30 Hz). Pacing of slow waves was blocked by tetrodotoxin (TTX) and atropine, suggesting phase advancement was mediated via intrinsic cholinergic nerves. Phase advancement and entrainment of slow waves via this mechanism was absent in W/W(V) mutants which lack intramuscular interstitial cells of Cajal (ICC-IM). These data suggest that neural regulation of slow wave frequency and regulation of smooth muscle responses to slow waves are mediated via nerve-ICC-IM interactions. With longer stimulation parameters (1.0-2.0 ms), EFS phase advanced and entrained slow waves in wild-type and W/W(V) animals. Pacing with 1-2 ms pulses was not inhibited by TTX or atropine. These data suggest that stimulation with longer pulse duration is capable of directly activating the pacemaker mechanism in ICC-MY networks. In summary, intrinsic excitatory neurons can phase advance and increase the frequency of antral slow waves. This form of regulation is mediated via ICC-IM. Longer pulse stimulation can directly activate ICC-MY in the absence of ICC-IM.

Enhancement of antral contractions and vagal afferent signaling with synchronized electrical stimulation

Gastric filling activates vagal afferents involved in peripheral signaling to the central nervous system (CNS) for food intake. It is not known whether these afferents linearly encode increasing contractions of the antrum during antral distension (AD). The aim of this study was to investigate effects of AD and electrically enhanced antral contractions on responses of vagal afferents innervating the antrum. Single-fiber recordings were made from the vagal afferents in anesthetized male Long-Evans rats. Antral contractions were measured with a solid-state probe placed in the antrum. A nonexcitatory electrical stimulation (NES) inducing no smooth muscle contractions was applied during the ascending phase of antral contractions to enhance subsequent antral contractions. Fifty-six fibers identified during AD (1 ml for 30 s) were studied through different types of mechanical stimuli. Under normal conditions, one group of fibers exhibited rhythmic firing in phase with antral contractions. Another group of fibers had nonrhythmic spontaneous firing. Responses of 15 fibers were tested with NES during multiple-step distension (MSD). NES produced a mean increase in antral contraction amplitude (177.1 +/- 35.3%) and vagal afferent firing (21.6 +/- 2.6%). Results show that both passive distension and enhanced antral contractions activate distension-sensitive vagal afferents. Responses of these fibers increase linearly to enhanced antral contraction induced by NES or MSD up to a distending volume of 0.6 ml. However, responses reached a plateau at a distending volume >0.8 ml. We concluded that enhanced contraction of the antrum can activate vagal afferents signaling to the CNS.

The effect of cisapride and ranitidine as monotherapies and in combination in the treatment of uncomplicated gastric ulceration

BACKGROUND

Stimulation of gastric motility has been supposed to accelerate the healing of gastric ulcer. The combination of the prokinetic drug cisapride and the H2 blocker ranitidine was tested in the treatment of uncomplicated gastric ulcer.

METHODS

Cisapride, 20 mg twice daily (Cis), and ranitidine, 150 mg twice daily (Ran), were given as monotherapies and in the combination 20 mg cisapride and 150 mg ranitidine daily (Cis + Ran) for a maximum of 8 weeks. The study was multicentre, randomized, and double-blind.

RESULTS

A total of 197 patients were included. Healing rates in the per-protocol analysis after 4 and 8 weeks' treatment were 61%/84%, 52%/69%, and 61%/92% for the Cis + Ran (n = 56), Cis (n = 58), and Ran (n = 59) treatment groups. No statistically significant difference in healing rates was seen when comparing Cis + Ran with the monotherapies. Symptom relief at the end of treatment was significantly better in the Ran group than in the Cis + Ran group with regard to epigastric pain (p = 0.01) and vomiting (p = 0.05). Patients' global evaluation of treatment was in favour of Ran in comparison with Cis + Ran treatment (p = 0.04).

CONCLUSIONS

Combination of cisapride and ranitidine in the treatment of gastric ulcer did not enhance the healing rate or improve symptom relief in patients treated for uncomplicated gastric ulcer when compared with the monotherapies.