OBJECTIVE To evaluate the tear film osmolality and electrolyte composition in healthy horses.
ANIMALS 15 healthy adult horses.
PROCEDURES Each horse was manually restrained, and an ophthalmic examination, which included slit-lamp biomicroscopy, indirect ophthalmoscopy, and a Schirmer tear test, was performed. Tear samples were collected from both eyes with microcapillary tubes 3 times at 5-minute intervals. The tear samples for each horse were pooled, and the osmolality and electrolyte concentrations were measured. The mean (SD) was calculated for each variable to establish preliminary guidelines for tear film osmolality and electrolyte composition in healthy horses.
RESULTS The mean (SD) tear film osmolality was 283.51 (9.33) mmol/kg, and the mean (SD) sodium, potassium, magnesium, and calcium concentrations were 134.75 (10), 16.3 (5.77), 3.48 (1.97), and 1.06 (0.42) mmol/L, respectively. The sodium concentration in the tear film was similar to that in serum, whereas the potassium concentration in the tear film was approximately 4.75 times that of serum.
CONCLUSIONS AND CLINICAL RELEVANCE Results provided preliminary guidelines with which tear samples obtained from horses with keratopathies can be compared. Measurement of tear film osmolality in these horses was easy and noninvasive. The tear film concentration of divalent cations was greater than expected and was higher than the divalent cation concentrations in the tear films of rabbits and humans. These data may be clinically useful for the diagnosis and monitoring of hyperosmolar ocular surface disease in horses.
Objective—To evaluate the hemodynamic effects
of orally administered carvedilol in healthy dogs
with doses that might be used to initiate treatment
in dogs with congestive heart failure.
Animals—24 healthy dogs.
Procedure—Dogs were randomly allocated to
receive carvedilol PO at a dose of 1.56, 3.125, or
12.5 mg, twice daily for 7 to 10 days; 6 dogs served
as controls. Investigators were blinded to group
assignment. Hemodynamic variables were recorded
prior to administration of the drug on day 1 and
then 2, 4, and 6 hours after the morning dose on
day 1 and days 7 to 10. Change in heart rate after IV
administration of 1 µg of isoproterenol/kg and
change in systemic arterial blood pressure after IV
administration of 8 µg of phenylephrine/kg were
recorded 2 and 6 hours after administration of
Results—Administration of carvedilol did not significantly
affect resting hemodynamic variables or
response to phenylephrine. The interaction of day
and carvedilol dose had a significant effect on resting
heart rate, but a significant main effect of
carvedilol dose on resting heart rate was not detected.
Increasing carvedilol dose resulted in a significant
linear decrease in heart rate response to isoproterenol.
Conclusions and Clinical Relevance—In healthy
conscious dogs, orally administered carvedilol at
mean doses from 0.08 to 0.54 mg/kg given twice
daily did not affect resting hemodynamics. Over
the dose range evaluated, there was a dose-dependent
attenuation of the response to isoproterenol,
which provided evidence of β-adrenergic receptor
antagonism. (Am J Vet Res 2005;66:637–641)
Objective—To determine the duration of effect and
the effect of multiple doses of topical ophthalmic
application of 0.5% proparacaine hydrochloride on
corneal sensitivity in clinically normal dogs.
Animals—8 clinically normal dogs.
Procedure—Dogs were randomly allocated to treatment
order in a 2 × 2 (period × treatment) crossover
study. Treatments consisted of topical application of
ophthalmic 0.5% proparacaine (1 drop or 2 drops at a
1-minute interval); treatments were applied to both
eyes. A Cochet-Bonnet aesthesiometer was used to
determine corneal touch threshold (CTT) before
corneal application, 1 and 5 minutes after corneal
application, and at 5-minute intervals thereafter for 90
Results—The CTT value before treatment differed
significantly from CTT values after treatment until 45
minutes after application in the 1-drop group and until
55 minutes after application in the 2-drop group. As
determined by use of the Cochet-Bonnet aesthesiometer,
a significantly greater anesthetic effect was
detected for the 2-drop treatment, compared with the
effect for the 1-drop treatment, at 30, 35, 40, 45, 50,
and 55 minutes after application. Maximal anesthetic
effect lasted for 15 minutes for the 1-drop treatment
and 25 minutes for the 2-drop treatment.
Conclusions and Clinical Relevance—Duration of
corneal anesthetic effect induced by topical ophthalmic
application of 0.5% proparacaine in dogs of
this study is considerably longer than that reported
elsewhere. Serial application of doses of 0.5%
proparacaine increases the duration and magnitude of
corneal anesthetic effects. (Am J Vet Res 2005;66:77–80)
Objective—To evaluate differences in response to ID
injection of histamine, phytohemagglutinin (PHA), and
Aspergillus organisms between clinically normal horses
and horses with recurrent airway obstruction
Animals—5 healthy adult horses and 5 adult horses
Procedure—Intradermal testing (IDT) was performed
on the neck with 2 positive control substances (histamine
and PHA) and a mixture comprising 5
Aspergillus species. Four concentrations of each test
substance plus a negative control substance were
used. Equal volumes (0.1 mL) of each test substance
were prepared to yield 15 syringes ([4 concentrations
of each test substance plus 1 negative control substance]
times 3 test substances) for each side of each
horse (ie, 30 syringes/horse). Intradermal injections
were administered; diameter of wheals was recorded
0.5, 4, and 24 hours after injection.
Results—Hypersensitive responses to ID injection of
histamine were detected 0.5 hours after injection, and
a delay in wheal formation after ID injection of
Aspergillus mixture 24 hours after injection was detected
in RAO-affected horses but was not observed in clinically
normal horses. No differences were detected
between the 2 groups after ID injection of PHA.
Conclusions and Clinical Relevance—RAO-affected
horses are hypersensitive to histamine, suggesting that
RAO is associated with a heightened vascular response
to histamine. Higher concentrations of Aspergillus mixture
may be needed to detect horses that are sensitive
to this group of antigens. Wheal reactions to Aspergillus
may be a delayed response, suggesting that IDT results
should be evaluated 0.5, 4, and 24 hours after ID injection.
(Am J Vet Res2005;66:1348–1355)
Objective—To evaluate the precision of intradermal
testing (IDT) in horses.
Animals—12 healthy adult horses.
Procedure—IDT was performed on the neck of each
horse by use of 2 positive control substances (histamine
and phytohemagglutinin [PHA]) and a negative
control substance. An equal volume (0.1 mL) for each
injection was prepared to yield a total of 20 syringes
([4 concentrations of each positive control substance
plus 1 negative control substance] times 2 positive
control substances times 2 duplicative tests) for each
side of the neck. Both sides of the neck were used for
IDT; therefore, 40 syringes were prepared for each
horse. Hair was clipped on both sides of the neck, and
ID injections were performed. Diameter of the skin
wheals was recorded 0.5, 4, and 24 hours after ID
Results—Intra- and interhorse skin reactions to ID
injection of histamine and PHA resulted in wheals of
uniform size at 0.5 and 4 hours, respectively.
Significant intra- and interhorse variation was detected
in wheals caused by PHA at 24 hours.
Conclusions and Clinical Relevance—ID injection of
histamine and PHA caused repeatable and precise
results at 0.5 and 4 hours, respectively.
Concentrations of 0.005 mg of histamine/mL and
0.1 mg of PHA/mL are recommended for use as positive
control substances for IDT in horses. This information
suggests that consistent wheal size is evident
for ID injection of control substances, and variation in
wheals in response to ID injection of test antigens
results from a horse's immune response to specific
antigens. (Am J Vet Res 2005;66:1341–1347)
Objective—To evaluate the effects of deracoxib and aspirin on serum concentrations of thyroxine (T4), 3,5,3′-triiodothyronine (T3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) in healthy dogs.
Procedure—Dogs were allocated to 1 of 3 groups of 8 dogs each. Dogs received the vehicle used for deracoxib tablets (PO, q 8 h; placebo), aspirin (23 to 25 mg/kg, PO, q 8 h), or deracoxib (1.25 to 1.8 mg/kg, PO, q 24 h) and placebo (PO, q 8 h) for 28 days. Measurement of serum concentrations of T4, T3, fT4, and TSH were performed 7 days before treatment (day −7), on days 14 and 28 of treatment, and 14 days after treatment was discontinued. Plasma total protein, albumin, and globulin concentrations were measured on days −7 and 28.
Results—Mean serum T4, fT4, and T3 concentrations decreased significantly from baseline on days 14 and 28 of treatment in dogs receiving aspirin, compared with those receiving placebo. Mean plasma total protein, albumin, and globulin concentrations on day 28 decreased significantly in dogs receiving aspirin, compared with those receiving placebo. Fourteen days after administration of aspirin was stopped, differences in hormone concentrations were no longer significant. Differences in serum TSH or the free fraction of T4 were not detected at any time. No significant difference in any of the analytes was detected at any time in dogs treated with deracoxib.
Conclusions and Clinical Relevance—Aspirin had substantial suppressive effects on thyroid hormone concentrations in dogs. Treatment with high dosages of aspirin, but not deracoxib, should be discontinued prior to evaluation of thyroid function.
Objective—To compare results of a nonradioactive
colorimetric microplate assay with results of a traditional
radioactive proliferation assay for determination
of its use as a reliable and accurate alternative
method for determination of proliferative activity of
Sample Population—Blood samples from 10 clinically
normal domestic shorthair cats.
Procedure—Double-density gradient separation was
used to isolate mononuclear cells. Isolated cells were
stimulated with various concentrations of concanavalin
A (Con-A) and cultured for 72 hours.
Lymphocyte proliferation was measured by radioactive
([3H]thymidine) and nonradioactive (colorimetric)
techniques. Immunophenotypic analysis with felinespecific
CD4+ and CD8+ monoclonal antibody was performed,
using flow cytometry.
Results—Mononuclear cells were successfully isolated
(97 to 99% purity and viability) from blood samples.
A similar dose-dependent proliferative response
to Con-A stimulation was measured with [3H]thymidine
incorporation and the colorimetric assay. For
both techniques, concentrations of 0.1 and 1.0 µg of
Con-A/ml were submitogenic, and 100 µg/ml was
toxic to cultured cells. For both techniques, maximal
proliferation was observed with 5 µg of Con-A/ml.
Conclusion and Clinical Relevance—These results
indicate that the nonradioactive colorimetric technique
is a reliable and accurate method for measuring
proliferative activity of feline lymphocytes. Clinically,
this assay can be used as part of a screening process
to determine immunocompetence of at-risk cats and
to evaluate treatments for cats with immune-mediated
or T-cell-dependent diseases. (Am J Vet Res 2001;
Objective—To determine ocular tissue drug concentrations after topical ocular administration of 0.3% ciprofloxacin and 0.5% moxifloxacin in ophthalmologically normal horses.
Animals—24 ophthalmologically normal adult horses.
Procedures—0.3% ciprofloxacin and 0.5% moxifloxacin solutions (0.1 mL) were applied to the ventral conjunctival fornix of 1 eye in each horse as follows: group 1 (n = 8) at 0, 2, 4, and 6 hours; group 2 (8) at 0, 2, 4, 6, and 10 hours; and group 3 (8) at 0, 2, 4, 6, 10, and 14 hours. Tears, cornea, and aqueous humor (AH) were collected at 8, 14, and 18 hours for groups 1, 2, and 3, respectively. Drug concentrations were determined via high-performance liquid chromatography.
Results—Median (25th to 75th percentile) concentrations of ciprofloxacin for groups 1, 2, and 3 in tears (μg/mL) were 53.7 (25.5 to 88.8), 48.5 (19.7 to 74.7), and 24.4 (15.4 to 67.1), respectively; in corneal tissue (μg/g) were 0.95 (0.60 to 1.02), 0.37 (0.32 to 0.47), and 0.48 (0.34 to 0.95), respectively; and in AH were lower than the limit of quantification in all groups. Concentrations of moxifloxacin for groups 1, 2, and 3 in tears (μg/mL) were 188.7 (44.5 to 669.2), 107.4 (41.7 to 296.5), and 178.1 (70.1 to 400.6), respectively; in corneal tissue (μg/g) were 1.84 (1.44 to 2.11), 0.78 (0.55 to 0.98), and 0.77 (0.65 to 0.97), respectively; and in AH (μg/mL) were 0.06 (0.04 to 0.08), 0.03 (0.02 to 0.05), and 0.02 (0.01 to 0.04), respectively. Corneal moxifloxacin concentrations were significantly higher in group 1 than groups 2 and 3.
Conclusions and Clinical Relevance—After topical ocular administration, fluoroquinolones can reach therapeutic concentrations in tears and corneal tissue of horses, even when there is an intact epithelium.
Objective—To determine whether ticlopidine exerts
an antiplatelet effect, estimate the pharmacodynamics
of ticlopidine, and evaluate any acute adverse
effects associated with administration of ticlopidine in
Animals—8 domestic purpose-bred sexually intact
Procedure—Ticlopidine was administered orally
(50 mg, q 24 h; 100 mg, q 24 h; 200 mg, q 24 h; and
250 mg, q 12 h). Each treatment period consisted of
10 days of drug administration. Platelet aggregation
studies with adenosine diphosphate (ADP) and collagen
and evaluation of oral mucosal bleeding times
(OMBTs) were performed on days 3, 7, and 10 during
each drug administration. Serotonin was measured to
evaluate secretion at baseline and on day 10 for cats
that received the 250-mg dosage.
Results—A significant reduction in platelet aggregation
was detected in response to ADP on days 7 and
10 at 100 mg, on day 3 at 200 mg, and on days 3, 7,
and 10 at 250 mg. A significant increase in the OMBT
and decrease in serotonin release on day 10 at 250
mg was also detected; however, the cats had anorexia
and vomiting at the 250-mg dosage.
Conclusions and Clinical Relevance—Although
there was a consistent antiplatelet effect at the
250-mg dosage, there was dose-dependent anorexia
and vomiting that we conclude precludes the clinical
usefulness of this drug in cats. ( Am J Vet Res 2004;65:327–332)