Objective— To evaluate effects of polymyxin B sulfate
(PMB) on response of horses to endotoxin, using
an ex vivo model.
Animals—8 healthy horses.
Procedure—In a crossover design, 3 doses of PMB
(100, 1,000, and 10,000 U/kg of body weight) and
physiologic saline solution (control) were evaluated.
Prior to and for 24 hours after administration of PMB,
blood samples were collected into heparinized tubes
for use in 2 assays. For the endotoxin-induced tumor
necrosis factor (TNF) assay, blood samples were incubated
(37 C for 4 h) with 1 ng of Escherichia coli or
Salmonella Typhimurium endotoxin/ml of blood.
Plasma was harvested and assayed. For the residual
endotoxin activity assay, plasma was collected into
sterile endotoxin-free borosilicate tubes, diluted 1:10
with pyrogen-free water, and incubated for 10 minutes
at 70 C. Escherichia coli endotoxin (0.1 or 1
ng/ml of plasma) was added to the thawed samples
prior to performing the limulus ameobocyte lysate
assay. Serum creatinine concentrations were monitored
for 1 week.
Results—Compared with baseline values, PMB
caused a significant dose- and time- dependent
decrease in endotoxin-induced TNF activity.
Compared with baseline values, residual endotoxin
activity was significantly reduced after administration
of 10,000 U of PMB/kg. Compared with baseline values,
1,000 and 5,000 U of PMB/kg should inhibit 75%
of endotoxin-induced TNF activity for 3 and 12 hours,
respectively. Serum creatinine concentrations
remained within the reference range.
Conclusion and Clinical Relevance—Results of the
study suggest that PMB is a safe, effective inhibitor of
endotoxin-induced inflammation in healthy horses.
( Am J Vet Res 2001; 62:72–76)
Objective—To compare physiologic, hematologic,
and selected serum and plasma biochemical variables
obtained from horses competing in 48-, 83-, or 159-
km endurance rides before competition and at the
same cumulative distance points.
Procedure—Weight and rectal temperature measurements
and blood samples were obtained from horses
before, during, and after 1 of 3 rides conducted on the
same day. Plasma protein (PP), lactate, WBC, serum
electrolyte, and calcium concentrations; PCV; and
creatine kinase (CK) activity were determined.
Assessments were made to determine whether any
differences among groups, with respect to total distance
competed, could be explained by differences in
lap speed or conditioning and to investigate the effect
of time in transit or on-site prior to competition on
results of blood analyses or competition outcome.
Results—Horses in the 159-km distance group had
the lowest preride serum sodium, chloride, bicarbonate,
and calcium concentrations. As hours in transit
increased, preride PP concentration was significantly
greater; serum sodium, chloride, and bicarbonate concentrations
were lower; CK activity at 159 km was
greater; and horses were more likely to be eliminated.
The preride sodium was significantly greater in horses
that completed the ride, compared with those
Conclusions and Clinical Relevance—Among distance
groups, distance ridden, speed, level of fitness,
and years of experience of horses had little effect on
the variables examined. Electrolyte and water supplementation
and earlier arrival at the event may be beneficial
for horses that are transported long distances
to endurance competition. (Am J Vet Res 2003;64:746–753)
Objective—To determine plasma endotoxin concentration
in horses competing in a 48-, 83-, or 159-km
endurance race and its importance with regard to
physical, hematologic, or serum and plasma biochemical
Procedure—Weight and rectal temperature measurements
and blood samples were obtained before, during,
and after exercise. Blood samples were analyzed
for plasma endotoxin concentration; serum antiendotoxin
antibody titers; thromboxane B2 (TxB2) and 6-
keto-prostaglandin F1α (PGF1α) concentrations; tumor
necrosis factor alpha (TNFα) and interleukin-6 (IL-6)
activities; WBC, plasma protein, lactate, serum electrolyte,
and calcium concentrations; PCV; and creatine
Results—Detection of plasma endotoxin increased
during exercise for horses competing at all distances
but occurred more frequently in the 48- and 83-km
groups. Plasma lactate concentration was significantly
greater when endotoxin was concurrently detected.
Endotoxin in plasma was not significantly associated
with success of race completion. Plasma TxB2
and PGF1α concentrations and serum IL-6 activity significantly
increased with exercise. Horses that had an
excellent fitness level (as perceived by their owners)
had greater decreases in serum antiendotoxin antibody
titers during exercise than did horses perceived
as less fit. In horses with better finish times, TxB2 and
PGF1α concentrations were significantly greater and
TNFα activity was significantly less than that of slower
Conclusions and Clinical Relevance—Endotoxemia
developed during endurance racing, but was significantly
correlated with increased plasma lactate concentration
and not with other variables indicative of
endotoxemia. Plasma TxB2 and PGF1α concentrations
and serum TNFα activity may be associated with performance
success. (Am J Vet Res 2003;64:754–761)
Case Description—Primary hypoaldosteronism without concurrent hypoadrenocorticism was diagnosed in an 8-year-old female alpaca with acute onset of weakness progressing to recumbency within 6 hours after onset.
Clinical Findings—Hematologic testing at admission revealed profound hyponatremia, hypochloremia, and acidemia with a normal blood potassium concentration. Further diagnostic testing, including an ACTH stimulation test, led to a diagnosis of hypoaldosteronism in conjunction with normal cortisol production.
Treatment and Outcome—The hembra responded well to IV polyionic fluid therapy with sodium supplementation and was managed successfully long term with free access to saline (0.9% NaCl) solution in addition to water ad libitum.
Clinical Relevance—To our knowledge, this is the first reported case of hypoaldosteronism in an alpaca. Hypoaldosteronism should be considered in alpacas as a possible differential diagnosis for refractory hyponatremia or for hyponatremia in which an underlying etiology is not determined.
OBJECTIVE To validate primer sets for use in reverse transcription quantitative PCR assays to measure gene expression of cytosolic phospholipase A2 (cPLA2) and microsomal prostaglandin E2 synthase 1 (mPGES1) in equine mononuclear cells and determine the effects of firocoxib, a selective cyclooxygenase 2 (COX-2) inhibitor, on COX-2, cPLA2, and mPGES1 gene expression following incubation of mononuclear cells with lipopolysaccharide (LPS).
ANIMALS 8 healthy adult horses.
PROCEDURES Peripheral blood mononuclear cells were isolated by density gradient centrifugation and incubated at 37°C with medium alone, firocoxib (100 ng/mL), LPS (1 ng/mL or 1 μg/mL), or combinations of firocoxib and both LPS concentrations. After 4 hours, supernatants were collected and tested for prostaglandin E2 (PGE2) concentration with an enzyme inhibition assay, and gene expression in cell lysates was measured with PCR assays.
RESULTS Primer pairs for cPLA2 and mPGES1 yielded single products on dissociation curve analyses, with mean assay efficiencies of 102% and 100%, respectively. Incubation with firocoxib and LPS significantly decreased PGE2 supernatant concentrations and significantly reduced COX-2 and mPGES1 gene expression, compared with values following incubation with LPS alone.
CONCLUSIONS AND CLINICAL RELEVANCE Primer sets for mPGES1 and cPLA2 gene expression in equine mononuclear cells were successfully validated. Firocoxib significantly decreased LPS-induced COX-2 and mPGES1 expression, suggesting that it may be useful in the control of diseases in which expression of these genes is upregulated.
Objective—To determine which antimicrobials that
are used to treat neonatal foals with septicemia attributable
to Escherichia coli will minimize endotoxin
release from bacteria and subsequent activity of
inflammatory mediators while maintaining bactericidal
Sample Population—Blood samples from 10 healthy
Procedure—Escherichia coli isolates A and B were
isolated from 2 septicemic foals, and minimal
inhibitory concentrations (MIC) were determined for
9 antimicrobials. Five of these antimicrobials were
tested in vitro at 2 and 20 times their respective
MIC. Whole blood or mononuclear cells grown in tissue-
culture media were incubated with 105 colonyforming
units of E coli and each antimicrobial or
saline (0.9% NaCl) solution. After 6 hours, number
of viable bacteria remaining was determined, and
supernatant was tested for endotoxin and tumor
Results—Testing in whole blood was compromised
by bactericidal effects of the blood itself. In mononuclear
cell suspensions, each antimicrobial significantly
reduced the number of viable bacteria to low or undetectable
amounts. Antimicrobials did not differ significantly
in efficacy of bacterial killing. Amikacin used
alone or in combination with ampicillin resulted in significantly
less endotoxin activity than did ampicillin,
imipenem, or ceftiofur alone. There was a correlation
between TNF-α and endotoxin activity.
Conclusions and Clinical Relevance—Aminoglycosides
appear less likely to induce endotoxemia
and TNF-α synthesis during bactericidal treatment of E
coli septicemia, compared with β-lactam antimicrobials.
Use of ampicillin, imipenem, or ceftiofur in the
treatment of septicemic neonatal foals should be
accompanied by appropriate treatment for endotoxemia.
(Am J Vet Res 2002;63:660–668)
Objective—To compare daily endogenous cortisol production rate and the pharmacokinetics of an IV bolus of hydrocortisone between neonatal foals and adult horses.
Animals—10 healthy full-term 2- to 4-day-old foals and 7 healthy adult horses.
Procedures—Blood samples were collected from each horse every 15 to 20 minutes for 24 hours for determination of 24-hour mean cortisol concentration. Afterward, dexamethasone (0.08 mg/kg) was administered IV to suppress endogenous cortisol production. Twelve hours afterward, hydrocortisone sodium succinate (1.0 mg/kg) was administered as a rapid IV bolus and serial blood samples were collected to determine hydrocortisone pharmacokinetics. Cortisol concentrations, daily cortisol production rate, and hydrocortisone pharmacokinetics were determined, and results were compared between adult horses and foals.
Results—The mean ± SD 24-hour cortisol concentration was significantly lower in foals (20 ± 4 ng/mL) than in horses (26 ± 6 ng/mL), but the daily cortisol production rate was significantly greater in foals (6,710 ± 320 ng/kg/d) than in horses (2,140 ± 400 ng/kg/d). For hydrocortisone, foals had a significantly greater volume of distribution at steady state (1.92 ± 1.11 L/kg) and total body clearance (1.39 ± 0.108 L/kg/h) and significantly lower peak plasma concentration (1,051 ± 343 ng/mL) than did horses (0.58 ± 0.15 L/kg, 0.349 ± 0.065 L/kg/h, and 8,934 ± 3,843 ng/mL, respectively).
Conclusions and Clinical Relevance—Important differences were detected in cortisol production and metabolism between neonatal foals and adult horses consistent with lower plasma protein binding of cortisol in foals. This decrease may contribute to cortisol insufficiency during prolonged critical illness in neonatal foals.
Objective—To determine concentrations of 2 acute-phase
proteins (serum amyloid A [SAA] and
lipopolysaccharide-binding protein [LBP]) in serum
samples obtained from horses with colic and identify
relationships among these acute-phase proteins and
Animals—765 horses with naturally developing gastrointestinal
tract diseases characterized by colic (ie,
clinical signs indicative of abdominal pain) and 79
healthy control horses; all horses were examined at 2
university teaching hospitals.
Procedure—Serum concentrations of SAA and LBP
were determined by immunoturbidometric and dotblot
Results—SAA and LBP concentrations were determined
for 718 and 765 horses with colic, respectively.
Concentrations of SAA were significantly higher in
nonsurvivors than in survivors, and horses with
enteritis or colitis and conditions characterized by
chronic inflammation (eg, abdominal abscesses, peritonitis,
or rectal tears) had SAA concentrations significantly
greater than those for horses with other conditions.
Serum concentrations of LBP did not correlate
with outcome, disease process, or portion of the
gastrointestinal tract affected.
Conclusions and Clinical Relevance—Circulating
concentrations of SAA were significantly higher at
admission in horses with colic attributable to conditions
having a primary inflammatory cause (eg, enteritis,
colitis, peritonitis, or abdominal abscesses) and
were higher in horses that failed to survive the
episode of colic, compared with concentrations in
horses that survived. Serum concentrations of LBP
did not correlate with survival. Analysis of these findings
suggests that evaluation of SAA concentrations
may be of use in identifying horses with colic attributable
to diseases that have inflammation as a primary
component of pathogenesis. (Am J Vet Res