Tissue contractility responses in paediatric intestinal pseudo-obstruction

Abstract

Objective and study: Paediatric intestinal pseudo-obstruction (PIPO) is a severe gastrointestinal motility disorder, characterized by functional obstruction of the small intestine in the absence of luminal occlusion. The diagnosis of PIPO is based on clinical picture supported by tests, namely antroduodenal manometry (ADM) and/or histopathology. However, there remains limited data regarding the tests' reliability and the clinical significance of specific findings. Organ bath contractility provides an opportunity to directly evaluate neuromuscular function of the intestine. We aim to evaluate and characterise small intestinal neuromuscular contractile patterns in PIPO patients as compared to tissue from non-PIPO controls. Methods: Small intestinal tissue was obtained from patients (with informed consent and full ethical approval) who required surgery, including those with PIPO and those presumed to have normal small intestinal neuromuscular function (absence of symptoms and/or signs) undergoing bowel surgery for other indications (e.g. bladder augmentation). After removal of the mucosa, longitudinal muscle strips (2x5 mm) were attached to an optical force transducer and maintained in physiological conditions. Spontaneous contractile activity was recorded, under a resting tension of 0.5g, followed by entrained electrical field stimulation (EFS; 40V, 0.3ms bipolar pulses, 30s in duration at 20Hz) in the absence or presence of drugs (Atropine, L-NAME and carbachol). Immunochemistry was used to examine neuromuscular structure and neuronal subtype composition. Contractile responses were compared between PIPO and non-PIPO controls. Results: Six PIPO patients (aged 4.17±2.04 years) and 11 controls (aged 9.27±4.90 years) were included. The frequency of contractions at baseline was significantly different between muscle strips from PIPO and control patients (4.95±3.84 vs 8.35±1.58 cycles/min; P=0.001; Figure 1A). Carbachol (1uM) induced sustained contraction at 4.03±2.47g and 4.07±1.91g in PIPO and control, respectively (P=0.972; Figure 1B). In PIPO samples, the area under the curve (AUC) upon EFS was 70.57±49.67g.s. In the presence of Atropine (1uM), this was reduced to 17.66±17.33g.s. Further addition of L-NAME (100uM) in the presence of atropine, resulted in a mean response of 9.92±11.57g.s. In controls, the AUC upon EFS was 71.51±44.21 g.s, changed to 14.17±13.79 g.s and 19.62±15.43g.s in the presence of atropine and further addition of L-NAME (Figure 1C). Apart from one PIPO sample where abnormal muscular layers were identified, SM22+ immunostaining demonstrated both circular and longitudinal muscle layers in all PIPO and control samples. There were also no discernible differences in neuronal networks or the presence of excitatory neurons (VAChT+ and Sub P+), and inhibitory neurons (nNOS+ and VIP+), between the two groups. Conclusions: This preliminary study shows promising utility of tissue contractility tests for the diagnosis and characterization of intestinal motility disorders. From this tissue-based study, contractile frequencies were found to be different between control and PIPO patients. Future work will seek to quantify neuronal subtype and neurotransmitter receptor composition, which might account for changes in the neuromuscular function of PIPO bowel.L6351749312021-06-08 <br />