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Small intestinal morphological integrity in horses suffering from pituitary pars intermedia dysfunction
The hypothesis of this study was that the morphological integrity of the small intestine is reduced in horses affected with pituitary pars intermedia dysfunction (PPID) compared to non PPID horses of similar age. The objective was to determine the morphological integrity of the proximal, mid and distal small intestinal mucosa in PPID and non PPID horses of similar age. Fifteen horses, 11 PPID and 4 non PPID (control) were donated for this study. Horses were of multiple breeds and genders (mare and gelding) across groups and were estimated to be over 25 yr of age. Horses were fed second cutting grass hay and senior feed at 1.8 and 0.5% of their BW, respectively, and monitored for medical stability for a period of 5 d prior to being subjected to an overnight dexamethasone suppression test (DST) to confirm the presence and assess the severity of the PPID condition. Horses were euthanized, the entire gastrointestinal tract removed and tissue samples were collected from the duodenum at 25 and 50 cm distal to the pyloric sphincter, the mid-jejunum and the ileum. Samples were prepared for histological visualization and morphometric analysis of the intestinal mucosa. Histological visualization of the intestinal mucosa was performed at 20× magnification and measurements of mucosal structures completed using a microscope imaging software at 10× magnification. For each segment, a minimum of 10 villi and associated crypts were measured for height, width, and crypt depth, respectively. Compared to control, villus height of PPID was lower in the 25 cm duodenum (P = 0.046) and tended to be lower in the 50 cm duodenum (P = 0.153) and mid-jejunum (P = 0.179). Villus height did not differ between treatments in the ileum. Villus crypt depth did not differ between PPID and control in the 25 cm duodenum and ileum, and was greater in the mid-jejunum (P = 0.027) and tended to be greater in the 50 cm duodenum (P = 0.092) in PPID compared to control. Villus width did not differ between PPID and control across any segment. In conclusion, the small intestinal integrity of PPID horses is reduced compared to non PPID horses of similar age, with a more pronounced effect in the proximal versus distal region of the small intestine.
Keywords: horse, pituitary pars intermedia dysfunction, intestinal morphology