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Chronic enteropathies in companion animals occur frequently. Due to a lack of information regarding the pathophysiology of these disorders, better characterization of these disorders is warranted.
Ussing chambers have been used to study intestinal membrane transport in many species. Since studies using a conventional circulating Ussing chamber require the collection of large tissue specimens, such studies have rarely been undertaken in small animal patients with spontaneously occurring gastrointestinal diseases. In order to overcome this disadvantage, an adapter modified Ussing chamber was investigated for evaluation of endoscopically obtained duodenal and colonic biopsies from dogs and cats in this study. Seventeen duodenal biopsies from five cats, 16 colonic biopsies from four cats, 51 duodenal biopsies from 14 dogs, and 13 colonic biopsies from four dogs were analyzed in the adapter modified Ussing chamber. Canine duodenal samples were grouped according to the WSAVA scoring system in combination with the presence of clinical symptoms. Group 1 was made up for healthy individuals (WSAVA score <2.7; n=8), group 2 was made up for animals exhibiting clinical signs of gastrointestinal disease, accompanied with histopathologically unremarkable biopsy samples (WSAVA score <2.7; n=15), group 3 was made up for dogs that showed clinical signs of gastrointestinal diseases and moderate to severe histopathological lesions (WSAVA score >3.0, n=32).
All biopsies were sequentially exposed to 40 mM glucose, 500 µM phloridzin, 200 µM histamine, 200 µM 5-hydroxytryptamine (5-HT), 4 µM prostaglandin (PGE2), and 5 µM forskolin. If the intestinal biopsy showed a response to the initial glucose stimulus, 40 mM glucose was once again applied at the end of the study in order to assess biopsy viability. Finally, the experiment was terminated by application of 600 µM ouabain.
Voltage (mV) and the membrane-generated short circuit current (Isc) were constantly recorded. To calculate the resistance, current pulses until reaching 18 µA were induced every 10 s for 0.5 s. Isc was measured in microamperes (µA), and conductance (mS/cm2) was calculated as the reciprocal value of resistance.
78.6% of all feline duodenal samples , 60.0% of all feline colonic samples, 49.0% of all canine duodenal samples, and 92.3% of all canine colonic samples responded to at least one chemical reagent by an appropriate change in Isc. In the canine duodenal biopsy subgroups, the rate of overall response ranged from 87.5% (group 1), to 63.3% (group 2), and 28.1% for biopsies of dogs of group 3.
Mean conductance of biopsies of all groups increased as the study progressed, indicating loss of tissue integrity over time. A high variation of conductance, baseline current, and the amplitude of current change could be observed within every group, within samples from the same animal, and for all substances that were applied.
It can be concluded, that duodenal and colonic biopsies of canine as well as feline patients maintain their transport ability ex vivo when quickly transferred into the modified Ussing chamber. The adapter modified Ussing chamber permits the use of distinct substances and the investigation of intestinal ion transport. This study demonstrates that the adapter modified Ussing chamber has the potential for becoming a valuable research tool in the study of duodenal and colonic transport in both healthy and diseased dogs and cats, but, because of the large variability, is of limited clinical use. Investigation of larger study populations, follow-up studies, as well as long term studies is warranted.