Objective—To assess pharmacokinetic and pharmacodynamic properties of dexamethasone administered PO as a solution or powder, compared with properties of dexamethasone solution administered IV, in apparently healthy horses.
Animals—6 adult horses.
Procedures—Serum cortisol concentration for each horse was determined before each treatment (baseline values). Dexamethasone (0.05 mg/kg) was administered PO (in solution or powdered form) or IV (solution) to horses from which feed had or had not been withheld (unfed and fed horses, respectively). Each horse received all 6 treatments in random order at 2-week intervals; PO and IV administrations of dexamethasone were accompanied by IV or PO sham treatments, respectively. Plasma dexamethasone and serum cortisol concentrations were assessed at predetermined intervals.
Results—Maximum plasma dexamethasone concentration after PO administration of powdered dexamethasone in unfed horses was significantly higher than the maximum plasma concentration after PO administration of dexamethasone solution in unfed or fed horses. Mean bioavailability of dexamethasone ranged from 28% to 66% but was not significantly different among horses receiving either formulation PO in the unfed or fed state. After dexamethasone treatment PO or IV, serum cortisol concentrations were significantly less than baseline at 1 to 72 hours in unfed horses and at 2 to 48 hours in fed horses.
Conclusions and Clinical Relevance—PO or IV administration of dexamethasone resulted in suppression of cortisol secretion in unfed and fed adult horses; the magnitude of suppression did not differ among treatment groups, and serum cortisol concentrations returned to baseline after 48 to 72 hours.
Objective—To evaluate clinical response, pulmonary
function, and adrenal gland response to incremental
doses of beclomethasone dipropionate in horses with
recurrent airway obstruction.
Animals—8 horses with recurrent airway obstruction.
Procedure—Horses randomly assigned to 4 groups
were treated twice daily via aerosol administration of
placebo or 500, 1,000, or 1,500 µg of beclomethasone
dipropionate in a crossover design with a 10-day
minimum washout period. Subjective assessment of
airway obstruction, serum cortisol concentration, and
maximum change in pleural pressure during tidal
breathing (ΔPplmax) were determined daily prior to
morning drug administration, and ΔPplmax was reevaluated
15 minutes after morning drug administration.
Pulmonary resistance and dynamic compliance were
determined at baseline and approximately 12 hours
after the final treatment.
Results—An immediate treatment effect was not
identified. Within 24 hours, ΔPplmax and airway
obstruction were lower in horses receiving
beclomethasone. Onset and magnitude of response
was similar among the 3 beclomethasone dose regimens.
Pulmonary resistance was improved only after
administration of all 3 doses of beclomethasone,
whereas dynamic compliance was improved after
administration of 1,000 µg and 1,500 µg of
beclomethasone. Reduction in serum cortisol concentration
occurred with all 3 beclomethasone dose
regimens; however, the magnitude of adrenal gland
suppression was greater in horses receiving 1,000 or
1,500 µg of beclomethasone.
Conclusions and Clinical Relevance—Low-dose
(500 µg) beclomethasone administration caused similar
improvement in pulmonary function, compared
with high-dose beclomethasone (1,000 and 1,500
µg), with the exception of dynamic compliance, and
caused less suppression of endogenous cortisol production.
(J Am Vet Med Assoc 2000;217:359–364)
Objective—To determine hyaluronan concentrations in peritoneal fluid from healthy horses and horses with sudden signs of severe abdominal pain and to identify the cellular sources of hyaluronan within the peritoneal cavity.
Animals—7 client-owned horses that were evaluated for sudden signs of severe abdominal pain, 6 healthy teaching horses, and 13 euthanized horses (11 with no abdominal disease and 2 that had undergone abdominal surgery 2 weeks previously for a different study).
Procedures—Abdominal fluid was collected from the client-owned and teaching horses. Hyaluronan concentrations were determined with an ELISA. Equine mesothelial cells were aseptically harvested from euthanized horses immediately after euthanasia, cultured, and processed for western blot immunoassays to detect expression of the following mesothelial cell markers: cytokeratins 8 and 18, vimentin, calretinin, mesothelin, and CD44. A reverse transcriptase–PCR assay was used to detect genetic expression of hyaluronan synthase-2 (HAS-2) from cultured and native equine tissue.
Results—The mean ± SD abdominal hyaluronan concentration in peritoneal fluid from horses with signs of abdominal pain (1,203.3 ± 46.3 ng/mL) was significantly greater than that in healthy horses (228.4 ± 167.3 ng/mL). Harvested cells were maintained, and immunoblotting analyses confirmed expression of the mesothelial markers. Gene expression of HAS-2 from cultured mesothelial cells and fibroblasts was confirmed.
Conclusions and Clinical Relevance—Peritoneal hyaluronan concentration was much higher in horses with severe abdominal pain than in healthy horses. Cultured equine mesothelial cells and fibroblasts can produce hyaluronan through HAS-2. Future investigation should focus on establishing the effect of exogenous hyaluronan administration on mesothelial cell function in horses with abdominal disease.