Objective—To determine effects of leukotriene (LT) C4 on ion transport across equine tracheal epithelium.
Sample—Tracheal epithelium from cadavers of 24 horses considered free of respiratory tract disease.
Procedures—Mucosae were mounted into Ussing chambers, and short-circuit current (Isc) was monitored over time. Effects of LTC4 were examined for various conditions, including addition of amiloride (10μM) to the mucosal bath solution, addition of bumetanide (10μM) to the serosal bath solution, addition of barium (1mM) to the serosal bath solution, and substitution of gluconate for chloride and HEPES for bicarbonate in bath solutions. Electrolyte transport was assessed via 22Na and 36Cl isotope fluxes.
Results—Addition of LTC4 (50nM) to the serosal bath solution caused an increase in Isc for basal conditions and a larger increase after pretreatment with amiloride. The increase was negated in part by the addition of bumetanide to the serosal bath solution and further reduced by substitution of HEPES for bicarbonate in bath solutions. Remaining current was reduced to values less than those before treatment with LTC4 by the addition of barium to the serosal solution. There was a small increase in Isc after the addition of amiloride and substitution of gluconate for chloride. Radioisotope flux indicated that addition of LTC4 to the serosal bath solution increased chloride secretion and reduced sodium absorption.
Conclusions and Clinical Relevance—LTC4 stimulated chloride secretion through a predominately bumetanide-sensitive pathway, with a smaller contribution from a bicarbonate-dependent pathway. Thus, LTC4 appears to be a potential mediator of airway hypersecretion in horses.
Objective—To compare the effects of oral administration
of omeprazole and ranitidine on gastric squamous
ulceration in Thoroughbreds in race training.
Design—Modified crossover study.
Animals—60 Thoroughbreds in race training with
gastric squamous mucosal ulceration.
Procedure—Horses were randomly allocated into 3
groups. Group 1 received no treatment for 28 days followed
by administration of omeprazole (4 mg/kg [1.8
mg/lb], PO, once daily) for 28 days; group 2 received
omeprazole (4 mg/kg, PO, once daily) for 28 days followed
by no treatment for 28 days; and group 3 received
ranitidine (6.6 mg/kg [3.0 mg/lb], PO, q 8 h) for 28 days
followed by administration of omeprazole (4 mg/kg, PO,
once daily) for 28 days. Ulceration was assessed endoscopically
at days 0, 28, 42, and 56. Lesions were scored
from 0 (no ulceration) to 3 (severe ulceration).
Results—After the initial 28 days of treatment, the
decrease in ulcer severity was significantly greater
after omeprazole treatment than after ranitidine treatment.
Ulcer severity decreased significantly in group
3 horses after 14 days of treatment with omeprazole.
Discontinuation of omeprazole resulted in worsening
of ulcer scores; however, ulcer scores at completion
of the study were less than at day 0. Horses that
received omeprazole after 28 days of ranitidine treatment
had a further reduction in ulcer severity.
Conclusions and Clinical Relevance—Omeprazole
was more effective than ranitidine in healing gastric
squamous ulcers in Thoroughbreds in race training.
Improvement was detected by 14 days and persisted
in most of the group 2 horses for at least 28 days after
omeprazole treatment was discontinued. (J Am Vet
Med Assoc 2005;227:1636–1639)
Objective—To characterize intragastric pH profiles in
critically ill foals and determine whether administration
of ranitidine altered pH profiles.
Design—Prospective observational study.
Animals—23 hospitalized neonatal foals ≤ 4 days of
Procedure—Intragastric pH was measured continuously for up to 24 hours by use of an indwelling electrode
and continuous data recording system. In 21
foals, ranitidine was administered IV.
Results—10 foals had predominantly or exclusively
alkaline profiles, 10 had profiles typical of those
reported for healthy foals, with periods of acidity
(hourly mean pH < 5.0 at least once), and 3 had atypical
profiles with periods of acidity. All 10 foals that
had intragastric pH profiles typical of healthy foals survived,
whereas only 2 foals with alkaline profiles survived,
and none of the foals with atypical profiles survived.
The effects of ranitidine administration could
not be assessed in 13 foals because of a high baseline
intragastric pH. In 7 of the remaining 9, ranitidine
administration resulted in an alkalinizing response,
but this response was often of blunted duration.
Ranitidine administration did not appear to alter the
intragastric pH profile in the remaining 2 foals.
Conclusions and Clinical Relevance—Results suggested that hospitalized critically ill foals often have
intragastric pH profiles different from those reported
for healthy foals and may respond differently to ranitidine
administration than do healthy foals. Many critically
ill foals have continuously alkaline intragastric pH
profiles, questioning the need for prophylactic administration
of ranitidine in all critically ill foals. (J Am Vet
Med Assoc 2001;218:907–911)
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
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 7.4) 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.
(Am J Vet Res 2002;63:744–749).
Objective—To identify factors associated with short-term survival in bacteremic neonatal foals, evaluate the racing performance of Thoroughbred survivors, and evaluate changes in causative organisms and their antimicrobial susceptibility.
Design—Retrospective case series.
Animals—423 bacteremic foals.
Procedures—Medical records of foals that were hospitalized in 1982 through 2007 were reviewed, and those with bacteremia were included in the study. Data retrieved included signalment, physical examination and clinicopathologic findings at admission, localized infections, concurrent illnesses, duration of hospitalization, and outcome (survival to discharge from the hospital vs nonsurvival). The number, identity, and antimicrobial susceptibility of organisms isolated from blood samples were also obtained. Racing records for surviving Thoroughbred foals and maternal siblings were examined.
Results—Of 423 bacteremic foals, 254 survived. Odds of survival were negatively associated with age at admission, septic arthritis, band neutrophil count, and serum creatinine concentration and positively associated with year of admission, diarrhea, rectal temperature, neutrophil count, and arterial blood pH. Overall, microbial culture of blood samples yielded 554 isolates; Escherichia coli was consistently isolated most frequently. Percentage of isolates susceptible to enrofloxacin, but no other antimicrobial, decreased over time. Surviving Thoroughbred foals did not differ from siblings with regard to percentage of starters, percentage of winners, or number of starts; however, surviving foals had significantly fewer wins and total earnings.
Conclusions and Clinical Relevance—During the study period, microbial resistance to antimicrobials commonly used to treat bacteremic foals did not develop. Surviving bacteremic Thoroughbred foals were as likely to start races as their siblings but earned less money.
Objective—To compare secretory responses to prostaglandin (PG) E2 in mucosa obtained from the proximal and distal portions of the colon of dogs.
Sample—Colonic mucosa from cadavers of 18 clinically normal adult dogs.
Procedures—Short-circuit current (ISC) and maximum change in ISC (ΔIsc) in response to administration of 1μM PGE2 were measured across mucosa obtained from the proximal and distal portions of the colon. Responses were evaluated in mucosa (n = 6 dogs) incubated in Ussing chambers with or without 1 mM amiloride or without chloride in the Ringer's bathing solution. Responses were also evaluated in mucosa (n = 9 dogs) incubated with or without pretreatment with 1 μM indomethacin, with or without amiloride in the subsequent bathing solution. Histologic changes in mucosa from 3 dogs were assessed over time.
Results—ISC and ΔISC were significantly reduced when chloride was removed from, but not when amiloride was added to, the bathing solution and were significantly reduced after pretreatment with indomethacin. The ΔISC was significantly greater in mucosa from the distal portion of the colon than in the proximal portion of the colon. Histologic changes after incubation for 3 hours were minimal.
Conclusions and Clinical Relevance—ISC and ΔISC resulted from electrogenic chloride secretion. Chloride secretion was reduced when release of PGs was prevented by indomethacin and was induced by administration of PGE2. Chloride secretion in response to PGE2 was greater in mucosa from the distal portion of the colon than in mucosa from the proximal portion of the colon.
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 BL-21) acupoint.
Animals—5 healthy adult horses, each with a gastric
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
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. (Am J Vet
OBJECTIVE To determine the effects of acepromazine maleate premedication on cardiovascular function before and after infusion of dobutamine hydrochloride for 30 minutes in isoflurane-anesthetized horses.
ANIMALS 6 healthy adult horses.
PROCEDURES Each horse was anesthetized once following premedication with acepromazine (0.02 mg/kg, IV) administered 30 minutes prior to anesthetic induction (ACP+ treatment) and once without premedication (ACP– treatment). Anesthesia was induced with IV administration of xylazine hydrochloride (0.8 mg/kg), ketamine hydrochloride (2.2 mg/kg), and diazepam (0.08 mg/kg). Horses were positioned in right lateral recumbency, and anesthesia was maintained via inhalation of isoflurane delivered in oxygen. End-tidal isoflurane concentration was adjusted to achieve a target mean arterial blood pressure of 60 mm Hg (interquartile range [25th to 75th percentile], 57 to 63 mm Hg) for at least 15 minutes. Cardiac index, oxygen delivery index, and femoral arterial blood flow indices were determined 60 minutes after anesthetic induction (baseline). Dobutamine was then infused to achieve a target mean arterial blood pressure of 80 mm Hg (interquartile range, 76 to 80 mm Hg). Data collection was repeated 30 minutes after the start of dobutamine infusion for comparison with baseline values.
RESULTS Complete data sets were available from 5 of the 6 horses. Dobutamine administration resulted in significant increases in oxygen delivery and femoral arterial blood flow indices but no significant change in cardiac index for each treatment. However, at baseline or 30 minutes after the start of dobutamine infusion, findings for the ACP+ and ACP– treatments did not differ.
CONCLUSIONS AND CLINICAL RELEVANCE In isoflurane-anesthetized horses, dobutamine administration increased oxygen delivery and femoral arterial blood flow indices, but these changes were unaffected by premedication with acepromazine.
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. ( J Am Vet Med Assoc 2004;225:
Objective—To determine prevalence of anthelmintic
resistance in cyathostome nematodes of horses in
the southern United States.
Animals—786 horses on 44 farms and stables in
Georgia, South Carolina, Florida, Kentucky, and
Procedure—Fecal egg count (FEC) reduction tests
were performed on 44 large farms and stables. Horses
on each farm were treated with an oral paste formulation
of fenbendazole, oxibendazole, pyrantel pamoate,
or ivermectin at recommended label dosages. A mixed
linear model was fitted to the percentage reduction in
FEC, accounting for differences among farms, states,
ages, treatments, and treatment by state interactions.
Results—By use of a conservative measure of resistance
(< 80% reduction), the percentage of farms with
anthelmintic-resistant cyathostomes was 97.7%, 0%,
53.5%, and 40.5% for fenbendazole, ivermectin, oxibendazole,
and pyrantel pamoate, respectively. Mean percentage
reductions in FEC for all farms were 24.8%,
99.9%, 73.8%, and 78.6% for fenbendazole, ivermectin,
oxibendazole, and pyrantel pamoate, respectively.
Pairwise contrasts between states for each treatment
revealed that in almost all instances, there were no significant
differences in results between states.
Conclusions and Clinical Relevance—The prevalence
of resistance found in this study was higher than that
reported previously, suggesting that anthelmintic resistance
in equine cyathostomes is becoming a major problem.
Furthermore, data from these 5 southern states,
which are geographically and physiographically distinct,
were remarkably similar. This suggests that drug resistance
in cyathostomes is highly prevalent throughout
the entire southern United States and probably nationwide.
(J Am Vet Med Assoc 2004;225:903–910)