Publications by authors named "Sarah B Elliott"

14 Publications

  • Page 1 of 1

Selected clinical, biochemical, and electrolyte alterations in anesthetized captive tigers (Panthera tigris) and lions (Panthera leo).

J Zoo Wildl Med 2014 Jun;45(2):328-34

A prospective study to assess changes in selected plasma biochemistry and electrolyte values, plasma insulin and aldosterone concentrations, and electrocardiography (ECG) was performed on eight female captive tigers (Panthera tigris) and three lions (Panthera leo) undergoing general anesthesia for elective laparoscopic ovariectomy. Each animal was sedated with medetomidine (18-25 microg/kg) and midazolam (0.06-0.1 mg/kg) intramuscularly, and anesthesia was induced with ketamine (1.9-3.5 mg/kg) intramuscularly and maintained with isoflurane. Venous blood samples were collected and analyzed for plasma biochemistry parameters and insulin and aldosterone concentrations. An ECG was recorded at the time of each blood sample collection. Mean plasma potassium, glucose, phosphorus, and aldosterone concentrations increased during anesthesia (P < or = 0.05). One tiger developed hyperkalemia (6.5 mmol/L) 2.5 hr after anesthetic induction. Plasma insulin concentrations were initially below the low end of the domestic cat reference interval (72-583 pmol/L), but mean insulin concentration increased (P < or = 0.05) over time compared with the baseline values. Three tigers and two lions had ECG changes that were representative of myocardial hypoxemia. Based on these results, continuous monitoring of clinical and biochemical alterations during general anesthesia in large nondomestic felids is warranted, and consideration should be given to reversal of medetomidine in these animals should significant changes in electrolytes or ECG occur.
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http://dx.doi.org/10.1638/2013-0202R.1DOI Listing
June 2014

Muscle and tendon heating rates with therapeutic ultrasound in horses.

Vet Surg 2013 Apr 1;42(3):243-9. Epub 2013 Feb 1.

Department of Large Animal Surgery, University of Tennessee Equine Medical Center, Knoxville, TN, USA.

Objective: To (1) determine the temperature change in equine tendon and muscle during therapeutic ultrasound and (2) develop guidelines for treating horses for muscular or tendinous injury using therapeutic ultrasound.

Study Design: Experimental, in vivo study.

Animals: Adult horses (n = 10).

Methods: Thermistors were inserted in the superficial and deep digital flexor tendons (SDFT and DDFT) of the thoracic limbs of 10 adult horses. On the left, 3.3 MHz therapeutic continuous ultrasound was done for 10 minutes at an intensity of 1.0 W/cm(2) and for the right thoracic limb at 1.5 W/cm(2). Thermistors were placed at 1 cm, 4 cm, and 8 cm depths in the epaxial muscles of the same 10 horses, for a 20-minute treatment at a frequency of 3.3 MHz and intensity of 1.5 W/cm(2). Temperature was recorded before, during, and after treatment. Data were statistically analyzed.

Results: Mean temperature rise was 3.5°C in the SDFT and 2.5°C in the DDFT at the end of the 1.0 W/cm(2) treatment (P = .94) and 5.2°C in the SDFT and 3.0°C in the DDFT at the end of the 1.5-W/cm(2) treatment (P = .48). Mean temperature rise in epaxial musculature was 1.3°C at a depth of 1.0 cm, 0.7°C at 4.0 cm, and 0.7°C at 8 cm.

Conclusions: The SDFT and DDFT are heated to a therapeutic temperature using a frequency of 3.3 MHz and intensity of 1.0 W/cm(2). The epaxial muscles are not heated to a therapeutic temperature using a frequency of 3.3 MHz and an intensity of 1.5 W/cm(2).
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http://dx.doi.org/10.1111/j.1532-950X.2013.01099.xDOI Listing
April 2013

Effects of low-dose oligofructose treatment administered via nasogastric intubation on induction of laminitis and associated alterations in glucose and insulin dynamics in horses.

Am J Vet Res 2009 May;70(5):624-32

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To ascertain whether laminitis can be induced via administration of oligofructose (OF) at doses of 5.0 and 7.5 g/kg in horses and to assess glucose and insulin dynamics before and after treatment.

Animals: 19 adult horses.

Procedures: Horses were fed OF (1.0 g/kg) mixed with oats for 6 days. Oligofructose at doses of 5.0 and 7.5 g/kg was then mixed with 4 L of water and administered (0 hours) to 8 (group A) and 4 (group B) horses, respectively, via nasogastric intubation; 8 horses received water alone. One horse in group A that did not develop laminitis was subsequently treated again and included in group B. Before and at intervals after treatment, resting plasma glucose and serum insulin concentrations were measured and frequently sampled IV glucose tolerance tests were performed. Area under the glucose curve (AUCg) and area under the insulin curve (AUCi) were calculated, and minimal model analyses were performed.

Results: 3 of 8 horses in group A and all 4 horses in group B developed laminitis. Significant treatment-time effects were detected for resting plasma glucose concentrations and AUCg. Among horses in group A, mean AUCg values at 24 and 48 hours were 34% and 32% higher, respectively, than the mean value at 24 hours. Treatment groups did not differ significantly with respect to resting serum insulin concentration, AUCi, or minimal model analysis results.

Conclusions And Clinical Relevance: In horses, laminitis can be induced and glucose dynamics altered via nasogastric administration of 5.0 g of OF/kg. An alteration in insulin dynamics was not detected following treatment with OF.
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http://dx.doi.org/10.2460/ajvr.70.5.624DOI Listing
May 2009

Effects of an intravenous endotoxin challenge on glucose and insulin dynamics in horses.

Am J Vet Res 2008 Jan;69(1):82-8

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To evaluate the effects of endotoxin administered IV on glucose and insulin dynamics in horses.

Animals: 16 healthy adult mares.

Procedures: Each week of a 2-week randomized crossover study, each horse received an IV injection (duration, 30 minutes) of Escherichia coli O55:B5 lipopolysaccharide (LPS) in 60 mL of sterile saline (0.9% NaCl) solution (20 ng/kg) or sterile saline solution alone (control treatment). Frequently sampled IV glucose tolerance test procedures were performed at 24 hours before (baseline) and 24 and 48 hours after injection; glucose and insulin dynamics were assessed via minimal model analysis.

Results: 13 of 16 horses had a clinical response to LPS, which was characterized by mild colic and leukopenia. Before treatment, mean +/- SD insulin sensitivity was 2.9 +/- 1.9 x 10(4) L x min(1) x mU(1); this significantly decreased to 0.9 +/- 0.9 x 10(4) L x min(1) x mU(1) 24 hours after treatment (69% reduction) and was 1.5 +/- 0.9 x 10(4) L x min(1) x mU(1) 48 hours after treatment. At baseline, mean +/- SD acute insulin response to glucose was 520 +/- 196 mU x min x L(1); this significantly increased to 938 +/- 620 mU x min x L(1) (80% increase) and 755 +/- 400 mU x min x L(1) (45% increase) at 24 and 48 hours after LPS treatment, respectively.

Conclusions And Clinical Relevance: Compared with baseline values, insulin sensitivity was decreased for 24 hours after IV injection of LPS, and affected horses had a compensatory pancreatic response. These disturbances in glucose and insulin dynamics may contribute to development of laminitis in horses.
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http://dx.doi.org/10.2460/ajvr.69.1.82DOI Listing
January 2008

Effects of long-term oral administration of levothyroxine sodium on glucose dynamics in healthy adult horses.

Am J Vet Res 2008 Jan;69(1):76-81

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To determine the effects of long-term oral administration of levothyroxine sodium (L-T(4)) on glucose dynamics in adult euthyroid horses.

Animals: 6 healthy adult mares.

Procedures: Horses received L-T(4) (48 mg/d) orally for 48 weeks. Frequently sampled IV glucose tolerance test procedures were performed on 3 occasions (24-hour intervals) before and at 16, 32, and 48 weeks during the treatment period. Data were assessed via minimal model analysis. The repeatability of measurements was evaluated.

Results: During treatment, body weight decreased significantly from the pretreatment value; mean +/- SD weight was 49 +/- 14 kg, 43 +/- 7 kg, and 25 +/- 18 kg less than the pretreatment value at weeks 16, 32, and 48, respectively. Compared with pretreatment findings, 1.8-, 2.4-, and 1.9-fold increases in mean insulin sensitivity (SI) were detected at weeks 16, 32, and 48, respectively; SI was negatively correlated with body weight (r = -0.42; P < 0.001). During treatment, glucose effectiveness increased and the acute insulin response to glucose decreased. Overall mean within-horse coefficients of variation were 5% and 29% for plasma glucose and serum insulin concentrations, respectively, and 33%, 26%, and 23% for SI, glucose effectiveness, and the acute insulin response to glucose, respectively.

Conclusions And Clinical Relevance: Long-term administration of L-T(4) was associated with weight loss and increased SI in adult euthyroid horses, although other factors may have confounded results. Levothyroxine sodium may be useful for the treatment of obesity and insulin resistance in horses, but further studies are required.
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http://dx.doi.org/10.2460/ajvr.69.1.76DOI Listing
January 2008

Effects of long-term oral administration of levothyroxine sodium on serum thyroid hormone concentrations, clinicopathologic variables, and echocardiographic measurements in healthy adult horses.

Am J Vet Res 2008 Jan;69(1):68-75

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To determine the effects of long-term oral levothyroxine sodium (L-T(4)) administration on serum thyroid hormone concentrations, thyroid gland function, clinicopathologic variables, and echocardiographic examination measurements in adult euthyroid horses.

Animals: 6 healthy adult mares.

Procedures: Horses received L-T(4) (48 mg/d) orally for 48 weeks. Every 4 weeks, physical examinations were performed; blood samples were collected for CBC, plasma biochemical analyses, and assessments of serum total triiodothyronine (tT(3)) and thyroxine (tT(4)) concentrations. Plasma creatine kinase MB activity and cardiac troponin I concentration were also measured. Echocardiographic examinations were performed before and at 16, 32, and 48 weeks during the treatment period.

Results: During the treatment period, mean body weight decreased significantly; heart rate varied significantly, but the pattern of variation was not consistent. Significant time effects were detected for certain clinicopathologic variables, but mean values remained within reference ranges. Cardiac troponin I was only detectable in 8 of 24 plasma samples (concentration range, 0.01 to 0.03 ng/mL). Serum creatine kinase MB activity did not change significantly over time. Compared with the pretreatment value, 5.4-, 4.0-, and 3.7-fold increases in mean serum tT(4) concentrations were detected at 16, 32, and 48 weeks, respectively. Some cardiac measurements changed significantly over time, but mean values remained within published reference ranges. Mean fractional shortening was lower than the pretreatment mean value at 16 and 32 weeks.

Conclusions And Clinical Relevance: In horses, long-term oral administration of 48 mg of L-T(4)/d significantly increased serum tT(4) concentrations and did not appear to adversely affect health.
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http://dx.doi.org/10.2460/ajvr.69.1.68DOI Listing
January 2008

In vitro effects of hydrochloric acid and various concentrations of acetic, propionic, butyric, or valeric acids on bioelectric properties of equine gastric squamous mucosa.

Am J Vet Res 2006 Nov;67(11):1873-82

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To compare the effects of hydrochloric acid (HCl) and various concentrations of volatile fatty acids (VFAs) on tissue bioelectric properties of equine stomach nonglandular (NG) mucosa.

Sample Population: Gastric tissues obtained from 48 adult horses.

Procedures: NG gastric mucosa was studied by use of Ussing chambers. Short-circuit current (Isc) and potential difference (PD) were measured and electrical resistance (R) and conductance calculated for tissues after addition of HCl and VFAs (5, 10, 20, and 40 mM) in normal Ringer's solution (NRS).

Results: Mucosa exposed to HCl in NRS (pH of 1.5 and, to a lesser extent, 4.0) had a significant decrease in Isc, PD, and R, whereas tissues exposed to acetic acid at a pH of < 4.0, propionic and butyric acids at a pH of
Conclusions And Clinical Relevance: The VFAs, especially acetic acid, in the presence of HCl at a pH of
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http://dx.doi.org/10.2460/ajvr.67.11.1873DOI Listing
November 2006

Effects of intravenously administrated omeprazole on gastric juice pH and gastric ulcer scores in adult horses.

J Vet Intern Med 2006 Sep-Oct;20(5):1202-6

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville 37996, USA.

The study was performed to evaluate the efficacy of omeprazole powder in sterile water, administered intravenously, on gastric juice pH in adult horses with naturally occurring gastric ulcers. Omeprazole (0.5 mg/kg, IV) was administered once daily for 5 days to 6 adult horses with gastric ulcers. Gastric juice was aspirated through the biopsy channel of an endoscope and pH was measured before and 1 hour after administration of omeprazole on day 1, and then before and after administration of omeprazole on day 5. Gastric ulcer scores were recorded on day 1 before administration of omeprazole and on day 5, 23 hours after the 4th daily dose. Gastric juice pH and ulcer scores were compared between the times. When compared with the pre-injection value (2.01 +/- 0.42), mean +/- SD gastric juice pH was significantly higher when measured 1 hour after administration of the initial dose (4.35 +/- 2.31), and before (5.27 +/- 1.74) and 1 hour after (7.00 +/- 0.25) administration of omeprazole on day 5. Nonglandular gastric ulcer number score significantly decreased from a mean +/- SD of 3.2 +/- 0.80 to 2.0 +/- 1.1, but nonglandular gastric ulcer severity score remained the same. Few glandular ulcers were seen in the study, and scores did not change. Because of its potent and long duration of action on gastric juice pH, this intravenous formulation of omeprazole may show promise for treatment of equine gastric ulcer syndrome (EGUS) in horses with dysphagia, gastric reflux, or other conditions that restrict oral intake of omeprazole paste. Aspiration of gastric juice and measurement of pH can be of use to determine whether the desired pH > 4.0 has been reached after omeprazole treatment.
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http://dx.doi.org/10.1892/0891-6640(2006)20[1202:eoiaoo]2.0.co;2DOI Listing
November 2006

Effects of dexamethasone and isoflupredone acetate on plasma potassium concentrations and other biochemical measurements in dairy cows in early lactation.

Am J Vet Res 2006 Jul;67(7):1244-51

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, 37996, USA.

Objective: To determine whether administration of isoflupredone acetate (ISO) to healthy cows increases the frequency of severe hypokalemia and whether dexamethasone (DEX) has detectable mineralocorticoid properties.

Animals: 33 cows at 20 to 25 days of lactation.

Procedures: Cows were randomly allocated to 5 treatment groups and received 2 IM injections (on days 0 and 2) of sterile saline (0.9% NaCl) solution (10 mL each), an injection of ISO (20 mg) or DEX (20 mg) followed by 10 mL of saline solution, or 2 injections of ISO or DEX. Milk production was measured, physical examinations were performed, and blood and urine samples were collected daily on days 0 through 7.

Results: Physical examination parameters did not differ among groups; however, 1 cow developed atrial fibrillation on day 4. Both corticosteroids significantly increased plasma glucose concentrations, and ISO significantly decreased plasma potassium concentrations and increased total carbon dioxide concentrations with time. One dose of ISO decreased mean plasma potassium concentration by 25% on day 2, compared with day 0, and severe hypokalemia (serum potassium concentration < 2.3 mEq/L) developed in 1 of 6 cows. Mean plasma potassium concentration was 46% lower on day 3 than on day 0 in cows receiving 2 doses of ISO, and 5 of 7 cows became severely hypokalemic. Mean urinary fractional excretion of potassium significantly increased from that on day 0 in cows receiving 2 doses of ISO.

Conclusions And Clinical Relevance: Both corticosteroids had glucocorticoid activity; however, only ISO had mineralocorticoid activity. Compared with saline solution, administration of 2 doses of ISO significantly increased the frequency of severe hypokalemia.
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http://dx.doi.org/10.2460/ajvr.67.7.1244DOI Listing
July 2006

Physical characteristics, blood hormone concentrations, and plasma lipid concentrations in obese horses with insulin resistance.

J Am Vet Med Assoc 2006 May;228(9):1383-90

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To compare obese horses with insulin resistance (IR) with nonobese horses and determine whether blood resting glucose, insulin, leptin, and lipid concentrations differed between groups and were correlated with combined glucose-insulin test (CGIT) results.

Animals: 7 obese adult horses with IR (OB-IR group) and 5 nonobese mares.

Procedures: Physical measurements were taken, and blood samples were collected after horses had acclimated to the hospital for 3 days. Response to insulin was assessed by use of the CGIT, and maintenance of plasma glucose concentrations greater than the preinjection value for > or = 45 minutes was used to define IR. Area under the curve values for glucose (AUC(g)) and insulin (AUC(i)) concentrations were calculated.

Results: Morgan, Paso Fino, Quarter Horse, and Tennessee Walking Horse breeds were represented in the OB-IR group. Mean neck circumference and BCS differed significantly between groups and were positively correlated with AUC values. Resting insulin and leptin concentrations were 6 and 14 times as high, respectively, in the OB-IR group, compared with the nonobese group, and were significantly correlated with AUC(g) and AUC(i). Plasma nonesterified fatty acid, very low-density lipoprotein, and high-density lipoprotein-cholesterol (HDL-C) concentrations were significantly higher (86%, 104%, and 29%, respectively) in OB-IR horses, and HDL-C concentrations were positively correlated with AUC values.

Conclusions And Clinical Relevance: Measurements of neck circumference and resting insulin and leptin concentrations can be used to screen obese horses for IR. Dyslipidemia is associated with IR in obese horses.
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http://dx.doi.org/10.2460/javma.228.9.1383DOI Listing
May 2006

A type IV P-type ATPase affects insulin-mediated glucose uptake in adipose tissue and skeletal muscle in mice.

J Nutr Biochem 2006 Dec 3;17(12):811-20. Epub 2006 Feb 3.

Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996-4500, USA.

Mice carrying two pink-eyed dilution (p) locus heterozygous deletions represent a novel polygenic mouse model of type 2 diabetes associated with obesity. Atp10c, a putative aminophospholipid transporter on mouse chromosome 7, is a candidate for the phenotype. The phenotype is diet-induced. As a next logical step in the validation and characterization of the model, experiments to analyze metabolic abnormalities associated with these mice were carried out. Results demonstrate that mutants (inheriting the p deletion maternally) heterozygous for Atp10c are hyperinsulinemic, insulin-resistant and have an altered insulin-stimulated response in peripheral tissues. Adipose tissue and the skeletal muscle are the targets, and GLUT4-mediated glucose uptake is the specific metabolic pathway associated with Atp10c deletion. Insulin resistance primarily affects the adipose tissue and the skeletal muscle, and the effect in the liver is secondary. Gene expression profiling using microarray and real-time PCR show significant changes in the expression of four genes--Vamp2, Dok1, Glut4 and Mapk14--involved in insulin signaling. The expression of Atp10c is also significantly altered in the adipose tissue and the soleus muscle. The most striking observation is the loss of Atp10c expression in the mutants, specifically in the soleus muscle, after eating the high-fat diet for 12 weeks. In conclusion, experiments suggest that the target genes and/or their cognate factors in conjunction with Atp10c presumably affect the normal translocation and sequestration of GLUT4 in both the target tissues.
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http://dx.doi.org/10.1016/j.jnutbio.2006.01.002DOI Listing
December 2006

Blood lipid concentrations and lipoprotein patterns in captive and wild American black bears (Ursus americanus).

Am J Vet Res 2006 Feb;67(2):335-41

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To compare blood lipid concentrations and lipoprotein patterns for captive and wild American black bears (Ursus americanus).

Animals: 7 captive and 9 wild adult (> or = 4 years old) black bears.

Procedure: Blood was collected from 2 groups of captive black bears (groups A and B) and 1 group of wild black bears (group C). Blood triglyceride (TG) and cholesterol concentrations were compared among groups. Plasma lipoproteins were isolated by use of a self-generating gradient of iodixanol, and lipoprotein patterns were compared between groups A and B.

Results: Captive bears (mean +/- SD, 187.8 +/- 44.4 kg) weighed significantly more than wild bears (mean, 104.8 +/- 41.4 kg), but mean body weight did not differ between groups A and B. Mean blood TG concentrations for groups B (216.8 +/- 16.0 mg/dL) and C (190.7 +/- 34.0 mg/dL) were significantly higher than that of group A (103.9 +/- 25.3 mg/dL). Mean blood cholesterol concentration was also significantly higher for group B (227.8 +/- 8.2 mg/dL) than for groups A (171.7 +/- 35.5 mg/dL) or C (190.8 +/- 26.8 mg/dL). Mean very-low-density lipoprotein TG and low-density lipoprotein cholesterol concentrations were 2- and 3-fold higher, respectively, for group B, compared with concentrations for group A.

Conclusions And Clinical Relevance: Blood lipid concentrations vary significantly among populations of black bears. Plasma lipoprotein patterns of captive bears differed significantly between colonies and may have reflected differences in diet or management practices.
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http://dx.doi.org/10.2460/ajvr.67.2.335DOI Listing
February 2006

Effects of dietary oils on the development of gastric ulcers in mares.

Am J Vet Res 2005 Nov;66(11):2006-11

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville 37996, USA.

Objective: To assess antiulcerogenic properties of 3 dietary oils.

Animals: 8 healthy adult mares.

Procedure: A protocol to induce gastric ulcers was used and included 240 mL of water plus corn oil, refined rice bran oil, or crude rice bran oil administered each day for 6 weeks according to a 4 x 4 Latin square randomized crossover design with 5-week washout intervals. A 7-day alternating feed deprivation period was included between weeks 5 and 6. Omeprazole was administered daily for the last 14 days of each washout interval. Endoscopic examinations of the stomach were performed at 0, 5, and 6 weeks, and the number (0 to 4 scale) and severity (0 to 5 scale) of ulcers were scored. Gastric fluid was collected at 0 and 5 weeks.

Results: Median body weight significantly increased by 29 kg (range, 10 to 50 kg). Mean +/- SE gastric fluid pH significantly decreased from 4.9 +/- 0.4 to 3.1 +/- 0.3 over 5 weeks, and total volatile fatty acid concentration significantly decreased over time. Mean +/- SE severity of nonglandular ulcers significantly increased from 0.4 +/- 0.1 to 1.2 +/- 0.2 over 5 weeks. Nonglandular ulcers significantly increased in number (mean +/- SE, 1.3 +/- 0.2 to 3.0 +/- 0.2) and severity (mean +/- SE, 1.2 +/- 0.2 to 2.6 +/- 0.2) during the 7-day alternating feed deprivation period. No effects of treatment were detected.

Conclusions And Clinical Relevance: In this model dietary oils did not prevent gastric ulcers from forming in the nonglandular portion of the stomach of horses.
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http://dx.doi.org/10.2460/ajvr.2005.66.2006DOI Listing
November 2005

Effects of oral administration of levothyroxine sodium on serum concentrations of thyroid gland hormones and responses to injections of thyrotropin-releasing hormone in healthy adult mares.

Am J Vet Res 2005 Jun;66(6):1025-31

Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.

Objective: To determine the effects of levothyroxine sodium (L-T4) on serum concentrations of thyroid gland hormones and responses to injections of thyrotropin-releasing hormone (TRH) in euthyroid horses.

Animals: 12 healthy adult mares.

Procedure: 8 horses received an incrementally increasing dosage of L-T4 (24, 48, 72, or 96 mg of L-T4/d) for weeks 1 to 8. Each dose was provided for 2 weeks. Four additional horses remained untreated. Serum concentrations of total triiodothyronine (tT3), total thyroxine (tT4), free T3 (fT3), free T4 (fT4), and thyroid-stimulating hormone (TSH) were measured in samples obtained at weeks 0, 2, 4, 6, and 8; 1.2 mg of TRH was then administered i.v., and serum concentrations of thyroid gland hormones were measured 2 and 4 hours after injection. Serum reverseT3 (rT3) concentration was also measured in the samples collected at weeks 0 and 8.

Results: Treated horses lost a significant amount of weight (median, 19 kg). Significant treatment-by-time effects were detected for serum tT3, tT4, fT3, fT4, and TSH concentrations, and serum tT4 concentrations were positively correlated (r, 0.95) with time (and therefore dosage) in treated horses. Mean +/- SD serum rT3 concentration significantly increased in treated horses (3.06 +/- 0.51 nmol/L for week 8 vs 0.74 +/- 0.22 nmol/L for week 0). Serum tT3, tT4, fT3, and TSH concentrations in response to TRH injections differed significantly between treated and untreated horses.

Conclusions And Clinical Relevance: Administration of levothyroxine sodium increased serum tT4 concentrations and blunted responses toTRH injection in healthy euthyroid horses.
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http://dx.doi.org/10.2460/ajvr.2005.66.1025DOI Listing
June 2005
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