Digestive enzyme concentrations and activities in healthy pancreatic tissue of horses.

OBJECTIVE: To measure concentrations and activities of major digestive enzymes in healthy equine pancreatic tissue. ANIMALS: 7 adult horses with normal pancreatic tissues. PROCEDURES: Small pieces of pancreatic tissue were collected immediately after euthanasia, immersed in liquid nitrogen, and maintained at -80 degrees C until analyzed. Concentrations and activities of amylase, lipase, chymotrypsin, trypsin, and elastase were determined by use of a microtiter technique. Relative pancreatic protein concentrations were determined by use of bovine serum albumin as the standard. Pancreatic DNA was extracted and con-centrations determined by use of the diphenylamine method with calf thymus DNA as the standard. RESULTS: The pancreatic cellular concentration of each enzyme, expressed as units per milligram of DNA, was consistent among horses. Cellular concentration of lipase (1,090.8 +/- 285.3 U/mg of DNA) was highest, followed by amylase (59.5 +/- 9.8 U/mg of DNA). Elastase, trypsin, and chymotrypsin were detected in small concentrations (1.9 +/- 0.6, 3.5 +/- 1.5, and 9.6 +/- 2.9 U/mg of DNA, respectively). Similar results were obtained for specific activities of the enzymes. CONCLUSIONS AND CLINICAL RELEVANCE: Results were unexpected because, under natural conditions, the predominant energy source for horses is carbohydrate. These results may indicate, in part, the reason horses seem to tolerate large amounts of fat added to their diet.

Role of cholecystokinin in the gastric motor response to a meal in horses.

OBJECTIVE: To measure plasma cholecystokinin (CCK) activity and the effect of a CCK-1 receptor antagonist on accommodation of the proximal portion of the stomach, and subsequent gastric emptying, in horses after ingestion of high-fat or high-carbohydrate meals. ANIMALS: 6 healthy adult horses with gastric cannulas. PROCEDURES: In the first study, horses were offered a high-fat (8% fat) or a high-carbohydrate (3% fat) pelleted meal of identical volume, caloric density, and protein content. Related plasma CCK-like activity was measured by radioimmunoassay (RIA). In a separate experiment, a horse was fed a grain meal with corn oil and phenylalanine, and plasma CCK activity was assessed by bioassay. A second study evaluated the effect of a CCK-1 receptor antagonist, devazepide (0.1 mg/kg, IV), on gastric accommodation and emptying following a meal of grain supplemented with either corn oil (12.3% fat) or an isocaloric amount of glucose (2.9% fat). Gastric tone was measured by a barostat and emptying by the (13)C-octanoic acid breath test. RESULTS: No plasma CCK-like activity was detected by RIA or bioassay before or after ingestion of meals. Preprandial devazepide did not alter the gastric accommodation response but did significantly shorten the gastric half-emptying time and time to peak breath (13)CO(2) content with the glucose-enriched meal. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, CCK participates in regulating the gastric motor response to a meal. Compared with other species, horses may be more responsive to carbohydrate than fat. A vagovagal reflex most likely mediates this regulation, with CCK as a paracrine intermediary at the intestinal level.

Meal-induced gastric relaxation and emptying in horses after ingestion of high-fat versus high-carbohydrate diets.

OBJECTIVE: To evaluate the effect of ingestion of a high-carbohydrate versus a high-fat meal on relaxation of the proximal portion of the stomach and subsequent gastric emptying in horses. ANIMALS: 6 healthy adult horses. PROCEDURE: The study consisted of 2 phases. In phase I, horses were offered a high-fat (8% fat) or a high-carbohydrate (3% fat) pelleted meal (0.5 g/kg) of identical volume, caloric density, and protein content. In phase II, meals consisted of a commercial sweet feed meal (0.5 g/kg) or this meal supplemented with corn oil (12.3% fat) or an isocaloric amount of glucose (2.9% fat). Proximal gastric tone was measured by variations in volume of an intragastric bag introduced through a gastric cannula and maintained with a constant internal pressure by an electronic barostat. Rate of gastric emptying was measured simultaneously with the 13C-octanoic acid breath test. Interaction between both techniques was studied in additional experiments. RESULTS: Meals with higher carbohydrate content induced a significantly more prolonged receptive relaxation of the proximal portion of the stomach than those with higher fat content, but the accommodation response was similar. Labeling the meals with the breath test marker influenced the accommodation response measured by the barostat. Gastric emptying rates were not significantly different between meals, although those high in carbohydrate initially emptied more slowly. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, in contrast to most species, dietary fat supplementation may not have a profound effect on gastric motility.

Evaluation of risk factors associated with development of postoperative ileus in horses.

OBJECTIVE: To determine factors associated with development of postoperative ileus (POI) in horses undergoing surgery for colic. DESIGN: Prospective case-control study. ANIMALS: 251 horses undergoing colic surgery, of which 47 developed POI. PROCEDURE: Signalment, history, clinicopathologic data, pre- and postoperative treatments, lesions, complications, costs, and outcome were recorded for all horses during hospitalization. RESULTS: Variables associated with increased odds of POI included small intestinal lesion, high PCV, and increased duration of anesthesia. There was modest evidence that pelvic flexure enterotomy and intraoperative administration of lidocaine may have reduced the odds of developing POI. CONCLUSIONS AND CLINICAL RELEVANCE: Findings during the preoperative and intraoperative periods can be used to identify horses at increased risk of POI. Reducing surgical and anesthetic duration should decrease the incidence of POI.

Effect of omeprazole paste on intragastric pH in clinically normal neonatal foals.

OBJECTIVE: To evaluate the efficacy of omeprazole paste, a commonly used antiulcer drug, on intragastric pH in clinically normal neonatal foals. ANIMALS: 6 clinically normal foals between 5 and 14 days of age. PROCEDURE: Intragastric pH was recorded in each foal by use of a disposable antimony pH electrode with internal reference. Values for intragastric pH were recorded every 4 seconds by use of an ambulatory pH monitor. There were two 24-hour recordings of intragastric pH for each foal, with 24 hours between recordings. Foals were not administered any drugs during the first recording. Foals were administered omeprazole paste (4 mg/kg, PO) 1 hour after the start of the second recording. Mean pH was calculated for each hour of each 24-hour recording session. Hourly mean values were compared between the first and second 24-hour recordings. RESULTS: Complete data were obtained from 4 of 6 foals during the first 24-hour recording and 6 of 6 foals during the second 24-hour recording. Foals had significantly higher mean hourly intragastric pH for hours 2 to 22 following omeprazole administration, compared with corresponding hourly pH values in foals during the first recording. CONCLUSION AND CLINICAL RELEVANCE: Omeprazole paste can effectively increase intragastric pH in clinically normal neonatal foals within 2 hours after oral administration of the first dose and can be administered to neonatal foals at the rate of 4 mg/kg, PO, every 24 hours.

Effects of exercise on gastric volume and pH in the proximal portion of the stomach of horses.

OBJECTIVE: To assess effects of exercise on a treadmill with changes in gastric volume and pH in the proximal portion of the stomach of horses. ANIMALS: 3 healthy adult horses. PROCEDURE: A polyester bag of approximately 1,600 mL was placed into the proximal portion of the stomach of each horse via a nasogastric tube. Changes in bag volume, determined by an electronic barostat, were recorded before, during, and after a training session on a treadmill with and without prior withholding of food. In separate experiments, pH in the proximal portion of the stomach was continuously recorded during exercise for fed and food-withheld conditions. Finally, changes in intra-abdominal and intragastric pressure were simultaneously recorded during a training session. RESULTS: Bag volume rapidly decreased to nearly zero during trotting and galloping. Conversely, a return to walking resulted in a sharp increase in volume and a return to pre-exercise values. Intragastric and intra-abdominal pressures increased almost in parallel with walking, trotting, galloping, and galloping on a slope. Gastric pH decreased rapidly to < 4 at the beginning of walking, continued to decrease during trotting and galloping, and remained low until a return to walking. CONCLUSIONS AND CLINICAL RELEVANCE: Increased intra-abdominal pressure during intense exercise in horses causes gastric compression, pushing acidic contents into the proximal, squamous-lined region of the stomach. Increased duration of acid exposure directly related to daily duration of exercise may be the reason that squamous lesions tend to develop or worsen when horses are in intensive training programs.

Effects of various diets on gastric tone in the proximal portion of the stomach of horses.

OBJECTIVE: To assess gastric tone in the proximal portion of the stomach in horses during and after ingestion of 4 diets (2 diets of grain and 2 diets of hay). ANIMALS: 6 adult horses. PROCEDURE: A polyester bag with a volume of approximately 1,600 ml was inserted through a gastric cannula into the proximal portion of the stomach of each horse. Internal pressure of the bag was maintained at 2 mm Hg by use of an electronic barostat, and changes in bag volume were recorded before, during, and after horses consumed diets of grain or hay. Each horse was fed 0.5 and 1.0 g of grain/kg and 0.5 and 1.0 g of hay/kg. Changes in bag volume measured by use of the barostat were indirectly related to changes in tone of the gastric wall. RESULTS: Food intake caused a distinctly significant biphasic increase in volume. The first phase was during active ingestion, which was followed shortly by a second, more prolonged postprandial phase. The ingestion-related phase of the response to intake of a diet of 1 g of hay/kg was significantly greater than that for the other diets. CONCLUSIONS AND CLINICAL RELEVANCE: ingestion of a solid meal induces a biphasic relaxation response in the proximal portion of the stomach of horses. Magnitude of the ingestion-related phase may be determined by size of the meal.

Evaluation of a method to experimentally induce colic in horses and the effects of acupuncture applied at the Guan-yuan-shu (similar to BL-21) acupoint.

OBJECTIVE: To evaluate the reliability of a method for inducing colic via small intestinal distention in horses and to examine the analgesic potential of bilateral electroacupuncture (EAP) at the Guan-yuan-shu (similar to BL21) acupoint. ANIMALS: 5 healthy adult horses, each with a gastric cannula. PROCEDURE: A polyester balloon connected to an electronic barostat was introduced into the duodenum via the gastric cannula. At 2 specified intervals (before and after commencement of EAP), the balloon was inflated to a barostat-controlled pressure that induced signs of moderate colic. Each inflation was maintained for 10 minutes. Heart and respiratory rates were continuously recorded. Frequency of various clinical signs of colic was recorded by 2 trained observers during various combinations of balloon inflation and EAP. Each horse received each of 5 treatment protocols (EAP at 20 Hz, sham EAP at 20 Hz, EAP at 80: 120 Hz dense:disperse, sham EAP at 80: 120 Hz dense:disperse, no treatment). Sham EAP was at a point located 2 cm lateral to the Guan-yuan-shu acupoint. RESULTS: Duodenal distention consistently induced a significant increase in frequency of signs of colic. None of the EAP protocols caused a significant reduction in frequency of these clinical signs during distention. CONCLUSIONS AND CLINICAL RELEVANCE: The method described is reproducible and highly controllable method for inducing colic that involved duodenal distention that should be useful in evaluating the efficacy of various analgesic strategies. Bilateral EAP at the Guan-yuan-shu acupoint was ineffective in reducing signs of discomfort induced by this method.

Effect of hydrochloric acid, pepsin, or taurocholate on bioelectric properties of gastric squamous mucosa in horses.

OBJECTIVE: To determine the effect of pH with or without pepsin or taurocholic acid on the bioelectric properties of gastric squamous mucosa in horses. SAMPLE POPULATION: Gastric tissues obtained from 16 adult horses that did not have evidence of gastric disease. PROCEDURE: Bioelectric properties of squamous mucosa were determined, using modified Ussing chambers. Tissues then were exposed to mucosal pepsin (1 mg/ml) or taurocholic acid (2.5 mM) under neutral (pH 74) or acidic (pH 1.7) conditions. RESULTS: Exposure of mucosal sheets to an acidic pH resulted in an immediate and sustained decrease in transmembrane potential difference and calculated tissue resistance. Pepsin or taurocholic acid did not significantly affect bioelectric variables when added to a mucosal bath solution of pH 7.4. A synergistic effect between pepsin or taurocholic acid and mucosal acidification was not detected. CONCLUSIONS AND CLINICAL RELEVANCE: Mucosal acidification with or without pepsin or taurocholic acid resulted in reduced tissue resistance. These data support the contention that squamous erosions or ulcers in horses are mediated, in part, by prolonged exposure of gastric squamous mucosa to luminal acid.