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- Author or Editor: Linda M. Van Hoogmoed x
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Abstract
Objectives—To determine the in vitro effect of prostaglandin E2 (PGE2), PGF2α, PGI2; and nonsteroidal anti-inflammatory drugs (NSAID; ie, flunixin meglumine, ketoprofen, carprofen, and phenylbutazone) on contractile activity of the equine dorsal colon, ventral colon, and pelvic flexure circular and longitudinal smooth muscle.
Animals—26 healthy horses.
Procedure—Tissue collected from the ventral colon, dorsal colon, and pelvic flexure was cut into strips and mounted in a tissue bath system where contractile strength was determined. Incremental doses of PGE2, PGF2α, PGI2, flunixin meglumine, carprofen, ketoprofen, and phenylbutazone were added to the baths, and the contractile activity was recorded for each location and orientation of smooth muscle.
Results—In substance P-stimulated tissues, PGE2 and PGF2α enhanced contractility in the longitudinal smooth muscle with a decrease or no effect on circular smooth muscle activity. Prostaglandin I2 inhibited the circular smooth muscle response with no effect on the longitudinal muscle. The activity of NSAID was predominantly inhibitory regardless of location or muscle orientation.
Conclusions and Clinical Relevance—In the equine large intestine, exogenous prostaglandins had a variable effect on contractile activity, depending on the location in the colon and orientation of the smooth muscle. The administration of NSAID inhibited contractility, with flunixin meglumine generally inducing the most profound inhibition relative to the other NSAID evaluated in substance P-stimulated smooth muscle of the large intestine. The results of this study indicate that prolonged use of NSAID may potentially predispose horses to develop gastrointestinal tract stasis and subsequent impaction. (Am J Vet Res 2000;61:1259–1266)
Abstract
Objective—To characterize the vascular anatomy of the third compartment of the stomach of llamas.
Animals—7 adult llamas.
Procedure—Immediately after each llama was euthanatized, vascular replicas of tissue from the third compartment were prepared by use of methylmethacrylate monomer and catalyst. Following chemical removal of tissue, the casts were further prepared for examination via scanning electron microscopy. By use of barium solution, microangiography was also performed on fixed tissue samples; the infused tissue was sectioned and imaged radiographically. Tissue samples were also collected for histologic evaluation after fixation and H&E staining.
Results—The third compartment was supplied by 4 pairs of primary arteries and veins located around the circumference of the structure. From these vessels, smaller arteries and veins branched to supply the serosal surface and penetrated deeper through the tunica muscularis to supply the submucosal and mucosal layers. An extensive capillary network was arranged in a hexagonal array surrounding the gastric glands, such that the mucosal aspect of the replicas had a honeycomb-like appearance. Histologically, variably sized villous projections lined by a single layer of epithelial cells with an extensive glandular network were observed.
Conclusions and Clinical Relevance—The third compartment of the stomach of llamas is a highly vascular structure with an extensive anastomotic capillary network at the luminal surface. Branching vessels provide extensive collateral circulation, and it appears that surgical incisions should heal well. Incisions in the third compartment should be oriented parallel to the longitudinal plane. (Am J Vet Res 2003; 64:346–350)
Abstract
Objective—To determine the in vitro effect of prostaglandin (PG) E2, PGF2α, and the nonsteroidal anti-inflammatory drugs (NSAIDs) indomethacin, ketoprofen, and nabumetone on the contractile strength of the circular smooth muscle layer of the third compartment of the stomach of llamas.
Sample Population—Specimens of the third compartment obtained from 5 healthy adult llamas.
Procedure—Full-thickness tissue samples were collected from the third compartment immediately after euthanasia. Specimens were cut into strips oriented along the circular muscle layer and mounted in a tissue bath system. Incremental amounts of ketoprofen, nabumetone, indomethacin, PGE2, and PGF2α were added, and contractile strength (amplitude of contractions) was recorded.
Results—Generally, PGE2 reduced contractile strength of the circular smooth layer of the third compartment, whereas PGF2α increased the strength of contractions. The activity of the NSAIDs was generally excitatory in a concentration-dependent manner, although significant changes were induced only by administration of indomethacin.
Conclusions and Clinical Relevance—On isolated smooth muscle strips of the third compartment of llamas, exogenous PGE2 and PGF2α had a variable effect on contractile strength. Administration of the NSAIDs did not inhibit contractility and would not be likely to induce stasis of the third compartment in the absence of an underlying disease process. (Am J Vet Res 2004;65:220–224
Abstract
Objective—To determine rate and degree of cooling for the superficial digital flexor tendon (SDFT) during a standard cryotherapy application in horses and evaluate in vitro effects of cooling on survival of tendon cells.
Sample Population—6 limbs of 5 adult horses and cultured cells obtained from SDFT of 3 adult horses during necropsy.
Procedure—In vivo data were acquired by use of a thermocouple temperature probe inserted into the SDFT of a forelimb of each standing sedated horse. After baseline temperatures were recorded, a commercial compression splint with circulating coolant was placed on each selected limb, which was then exposed to cold treatment for 60 minutes. Temperatures were recorded at 30-second intervals. Mean minimum core temperature was calculated and used to design a protocol for in vitro cold treatment of cells. Specimens were obtained from the SDFT of horses during necropsy; tendon cells were cultured in suspension and exposed to 1-hour of cold treatment that mimicked the in vivo procedure. Viability of cells after cold treatment was compared with viability of cells maintained at body temperature.
Results—After 1 hour of cold treatment, SDFT core temperature was reduced by a mean of 21.8°C, reaching a mean minimum temperature of 10oC. Viability did not differ significantly between cold-treated and control cells.
Conclusion and Clinical Relevance—Results indicated that topical application of cryotherapy significantly reduced core SDFT temperature in standing sedated horses. Temperatures achieved in vivo during cold treatment were not detrimental to the in vitro viability of tendon cells. (Am J Vet Res 2003;64:835–844)
Abstract
Objective—To determine the role of nitric oxide and an apamin-sensitive nonadrenergic noncholingeric inhibitory transmitter on contractility of the ventral colon of horses.
Sample population—Strips of the circular and longitudinal muscle layers and taenia of the ventral colon from 14 horses.
Procedure—Muscle strips were suspended in tissue baths and attached to force transducers. Contractile activity of circular, longitudinal, and taenia muscle strips in response to electrical field stimulation was measured after addition of apamin and a nitric oxide inhibitor, N-nitro-L-arginine methyl ester (L-NAME).
Results—Electrical field stimulation reduced contractile activity in the circular muscle layer and taenia but not the longitudinal muscle layer. Addition of L-NAME significantly reduced inhibitory contractile activity at all frequencies for the circular muscle layer, whereas a significant effect was evident for the taenia only at the highest frequency. The combination of L-NAME and apamin resulted in a significant reduction in inhibition of the taenia at all frequencies but for circular muscle only at lower frequencies.
Conclusions and Clinical Relevance—Nitric oxide and an apamin-sensitive neurotransmitter appear to mediate a component of inhibitory transmission in the circular muscle and taenia, but not the longitudinal muscle layer, of the equine ventral colon. Nitric oxide has a role in regulating contractile activity of the equine ventral colon, and nitric oxide synthase inhibitors may be useful in horses with ileus of the large colon. (Am J Vet Res 2000;61:64–68)
Abstract
Objective—To evaluate the efficacy of intraluminal administration of a customized solution during low-flow ischemia and reperfusion in the jejunum of horses.
Sample Population—Segments of jejunum obtained from 13 healthy adult horses.
Procedure—In isolated segments of jejunum maintained in an extracorporeal circuit, arterial flow was reduced to 20% of baseline for 40 minutes (ischemia) followed by 60 minutes of reperfusion. In 2 groups, a customized solution (concentrations, 12.5 and 25%, respectively) was placed in the lumen prior to lowflow ischemia and maintained during reperfusion. The control group received intraluminal lactated Ringer's solution for the same duration. Various metabolic, hemodynamic, histologic, and permeability variables were recorded.
Results—The 12.5% solution resulted in less histomorphologic injury and reduced mucosal permeability to albumin, compared with the 25% solution and the lactated Ringer's solution. Morphologic injury and permeability were reduced in tissues that received the 25% solution, compared with the control group, but this difference was not significant.
Conclusions and Clinical Relevance—Use of a 12.5% customized solution appeared to minimize injury in the isolated extracoporeal jejunal loop, which provides some indication that it might be useful in clinical situations. (Am J Vet Res 2002;63:1389–1394)
Abstract
Objective—To evaluate the effects of morphine administration for 6 days on gastrointestinal tract function in healthy adult horses.
Animals—5 horses.
Procedures—Horses were randomly allocated into 2 groups in a crossover study. Horses in the treatment group received morphine sulfate at a dosage of 0.5 mg/kg, IV, every 12 hours for 6 days. Horses in the control group received saline (0.9% NaCl) solution at a dosage of 10 mL, IV, every 12 hours for 6 days. Variables assessed included defecation frequency, weight of feces produced, intestinal transit time (evaluated by use of barium-filled spheres and radiographic detection in feces), fecal moisture content, borborygmus score, and signs of CNS excitement and colic.
Results—Administration of morphine resulted in gastrointestinal tract dysfunction for 6 hours after each injection. During those 6 hours, mean ± SD defecation frequency decreased from 3.1 ± 1 bowel movements in control horses to 0.9 ± 0.5 bowel movements in treated horses, weight of feces decreased from 4.1 ± 0.7 kg to 1.1 ± 0.7 kg, fecal moisture content decreased from 76 ± 2.7% to 73.5 ± 2.9%, and borborygmus score decreased from 13.2 ± 2.9 to 6.3 ± 3.9. Mean gastrointestinal transit time was also increased, compared with transit times in control horses.
Conclusions and Clinical Relevance—Morphine administered at 0.5 mg/kg twice daily decreased propulsive motility and moisture content in the gastrointestinal tract lumen. These effects may predispose treated horses to development of ileus and constipation.
Abstract
Objective—To determine whether a customized solution could attenuate the effects of low-flow ischemia and reperfusion injury of the equine jejunum.
Sample Population—A segment of jejunum obtained from 21 healthy adult horses.
Procedure—A segment of jejunum was maintained in an isolated extracorporeal circuit, and arterial flow was reduced to 20% of baseline for 40 minutes (ischemia) followed by 60 minutes of reperfusion. In 1 group, a customized solution was infused at a rate of 1 ml/min during low-flow ischemia and 3 ml/min during reperfusion. In a second group, the solution was infused at the same rate during low-flow ischemia, but it was infused at a rate of 7 ml/min during reperfusion. Control groups received lactated Ringer's solution administered at the same rates as for the customized solution. Various metabolic, hemodynamic, histologic, and permeability variables were recorded.
Results—A lower flow rate during reperfusion (3 ml/min) had a beneficial effect, compared with lactated Ringer's solution or the higher flow rate (7 ml/min). Use of the solution at this rate resulted in less histomorphologic injury and reduced mucosal permeability to albumin.
Conclusions and Clinical Relevance—Use of a customized solution at a lower flow rate during repurfusion appeared to have a protective effect on equine jejunum when administered IV during low-flow ischemia and reperfusion. (Am J Vet Res 2001; 62:1679–1686)
Abstract
Objective—To evaluate the effect of 2 cyclooxygenase (COX)-2 inhibitors on contractile activity of the circular smooth muscle layer of the equine dorsal and ventral colon.
Sample Population—Samples of the dorsal and ventral colon obtained from 10 healthy horses.
Procedure—Full-thickness tissue samples were collected from the dorsal colon in the area of the diaphragmatic flexure and the ventral colon in the area of the sternal flexure. Samples were cut into strips oriented along the fibers of the circular muscle layer and mounted in a tissue bath system for determination of contractile strength. Incremental amounts of etodolac, nabumetone, and indomethacin were added, and contractile activity was recorded.
Results—Response of the dorsal and ventral colon to nonsteroidal anti-inflammatory drugs (NSAIDs) was variable. Indomethacin induced the greatest reduction in contractile activity, followed by nabumetone. For etodolac, the difference from baseline values was only significantly reduced at the highest concentration used (1 × 10–5M) for the ventral colon.
Conclusions and Clinical Relevance—The NSAIDs that are designed to target the COX-2 isoform appeared to have variable effects on the contractile activity of the equine dorsal and ventral colon. Etodolac appeared to have the least effect on contractile activity, compared with the effects attributable to nabumetone, and would potentially have the fewest adverse effects relative to motility of the dorsal and ventral colon. (Am J Vet Res 2002;63:1496–1500)
Abstract
Objective—To determine efficacy of an extracorporeal circuit to maintain a segment of equine large colon for 3.5 hours and to evaluate the effect of low arterial flow on histologic and metabolic variables.
Sample Population—Segments of large colon from 15 healthy adult horses.
Procedure—The pelvic flexure was surgically removed and maintained in an isolated circuit. In the control group, tissue was evaluated for 3.5 hours, whereas in the low-flow group, arterial flow was reduced to 20% of baseline for 40 minutes followed by 2 hours of reperfusion. Various metabolic and hemodynamic variables were evaluated at 30-minute intervals. Effects of nitric oxide (NO) and L-N-nitro-arginine- methyl-ester (L-NAME) on contractile activity were determined, and histomorphologic evaluation was performed at the completion of the study.
Results—Low-flow ischemia with reperfusion caused significant histomorphologic differences, compared with the control group. In the low-flow group, significant differences included reduction in PaCO2, reduction in bicarbonate concentrations, increase in PaO2, and an increase in base deficit in arterial and venous blood samples. Other significant differences included increases in PCV, protein concentration, total WBC count, and albumin clearance for the low-flow group. Differences were not detected in inhibitory activity of the low-flow group relative to the control tissue with or without addition of NO and L-NAME.
Conclusion—The extracorporeal circuit maintained a segment of equine intestine for 3.5 hours and can be used to simulate ischemic injury. The extracorporeal circuit provides the potential to investigate pharmaceutic agents that can minimize intestinal injury. (Am J Vet Res 2000;61:1042–1051)
