Pharmacology in horses involves the study and application of drugs and medications to diagnose, treat, and prevent diseases and conditions in equine species. This field encompasses the understanding of pharmacokinetics and pharmacodynamics specific to horses, including how drugs are absorbed, distributed, metabolized, and excreted by the equine body. Commonly studied pharmacological agents in horses include non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics, sedatives, and anthelmintics. Research in equine pharmacology focuses on determining appropriate dosages, understanding drug interactions, and minimizing adverse effects. This page compiles peer-reviewed research studies and scholarly articles that investigate the efficacy, safety, and regulatory aspects of pharmacological interventions in equine veterinary practice.
Benson GJ, Thurmon JC.Anticholinergics, tranquilizers, and sedative-hypnotics are the usual agents used for preanesthetic sedation of the horse. Of these drugs, the anticholinergics are of little importance in the horse. Acepromazine is the most useful and widely used tranquilizer, whereas xylazine is a safe and popular sedative. A newer sedative recently made available to the veterinarian for clinical use in horses is detomidine. Thiobarbiturates are seldom used alone any longer but are still useful when combined with guaifenesin for induction and maintenance of anesthesia. Other, more contemporary drug combinatio...
Brunson DB.When compared with halothane, isoflurane has several distinct characteristics. Vaporizer settings are higher because of its lower potency. Respiratory rates will be slower, and intraoperative changes in depth and recovery from surgical depth of anesthesia will be more rapid, although total recovery times frequently will not be different. Halothane and isoflurane appear similar in their effects on ocular reflexes and mean arterial blood pressure. Recovery from isoflurane should be managed to provide added sedation or physical support if the horse attempts to stand prematurely.
Hildebrand S.In summary, neuromuscular blocking agents can be used safely and to advantage in equine anesthesia. Muscle-relaxant use in equine anesthesia has been helped by the development of new relaxants such as atracurium, which has a reliable and reproducible duration of action. There are certain cases that benefit particularly by the use of relaxants but their use is not limited to these cases. These cases involve horses that experience persistent movement and hypotension during anesthesia, are undergoing ophthalmic or abdominal surgery or fracture repair, or are severely ill. Horses receiving muscle ...
Daunt DA.In conclusion, vigilant supportive care is necessary to prevent morbidity and death in the anesthetized horse. Because some of the equipment and drugs are specialized and the consequences of some postanesthetic complications are severe, availability of those items must be confirmed prior to anesthesia. Proper positioning and padding will help to reduce the incidence of postanesthetic myopathy-neuropathy syndrome in these large patients. Adequate tissue perfusion is important and can be achieved by controlling anesthetic depth, increasing intravascular volume with fluid administration, and by a...
Snow DH, Frigg M.The bioavailability of ascorbic acid administered to thoroughbreds by intramuscular injection was investigated. For intramuscular injection two preparations were studied, and the percentage bioavailability up to 24 h of 10 g of ascorbic acid was 95% +/- 22 in four horses and 60% in two horses with preparations A and B, respectively. Bioavailability at 24 h in three horses injected subcutaneously with 10 g of preparation B was 82%. Intramuscular injection of both preparations was apparently well tolerated while subcutaneous injection of preparation B (pH 6.0) was associated with marked irritanc...
King JN, Gerring EL.The effect of pre-treatment with a selective platelet-activating factor (PAF) antagonist, WEB 2086, on the actions of low-dose endotoxin was evaluated in ponies prepared with gastrointestinal strain gauges. Endotoxin (0.1 microgram/kg i.v.) produced a marked reduction in gastric contraction amplitude and rate, and an increased frequency and reduced duration of jejunal phase III activity fronts (AFs). WEB 2086 (6.6 mg/kg) administered i.v. 10 min before the endotoxin, produced significant antagonism (P less than 0.001) of the effect of endotoxin on gastric contraction amplitude and rate. The co...
Tranquilli WJ, Thurmon JC.Several unique pharmacologic and physiologic factors must be considered when attempting to anesthetize premature or neonatal foals. Juvenile foals are similar to adults in their physiology and metabolism. Anesthetic drug and protocol selection should reflect the differences between these two age groups. Neonates are best anesthetized using an inhalation technique, whereas older foals can be safely anesthetized with either parenteral or inhalation anesthetic agents. Careful monitoring is absolutely essential when anesthetizing foals. The clinician should plan to routinely administer fluids and ...
Pemberton AD, Hodgson JC, Gilmour JS, Doxey DL.Isolates were prepared from the sera of 12 horses with acute grass sickness, using methods reported to yield serum fractions associated with neurotoxicity, and their components identified by liquid chromatography and spectroscopy. All isolates were found to contain cortisol and six isolates also contained a degradation product of an analgesic drug, dipyrone. However, no recognised neurotoxin was detected.
Leblanc PH, Eberhart SW.This study was designed to determine whether the epidural administration of an alpha2 agonist, xylazine, would produce measurable changes in arterial blood pressure, electrocardiographic (ECG) activity and arterial blood gas values in horses. Six horses were given each of four treatments: epidural xylazine, intravenous xylazine, epidural lidocaine and epidural saline. A carotid artery catheter was used to measure arterial blood pressure and to collect samples for blood gas analysis before treatment and at intervals post treatment. Heart rate, arterial pressures, ECG activity and respiratory ra...
Carter SW, Robertson SA, Steel CJ, Jourdenais DA.Six healthy foals underwent instrumentation for measurement of the cardiopulmonary effects of sedation with 1.1 mg/kg bodyweight xylazine hydrochloride given intravenously. Responses to xylazine in foals at 10 and 28 days of age were not significantly different. Foals became sedate and markedly ataxic, and four of the six foals became recumbent. Heart rate decreased significantly but no arrhythmias were detected. Arterial blood pressure increased initially and then fell significantly below pre-injection values. Changes in respiratory airflow, upper airway obstruction and respiratory noise were...
Mogg TD, Pollitt CC, Willmore JP, Thompson H.Three groups of horses and ponies (N = 13, 13 and 12) were treated with ivermectin paste (0.2 mg/kg p.o.), avermectin B1 solution (0.2 mg/kg p.o.), or fenbendazole suspension (10 mg/kg via nasogastric tube). The avermectin B1 was a 1% solution in a propylene glycolglycerol formal base. Faecal strongyle egg counts were performed before, and 14, 28, 42, 56 and 70 d, after treatment. Full-thickness skin biopsies from the neck, pectoral and umbilical regions were examined for Onchocera microfilaria before treatment, and again 14 and 70 d later. Ivermectin therapy produced a significant (P less tha...
Hunt RJ, Allen D, Moore JN.Using a pump-perfused extracorporeal isolated digital preparation, the effects of a 30-minute infusion of either saline solution (control) or endotoxin on equine digital hemodynamics and microvascular function were determined. Digital blood flow and arterial, venous, and capillary pressures were recorded at 15-minute intervals for 150 minutes. From these data, total vascular resistance and pre- and postcapillary resistances were calculated. Isogravimetric capillary filtration coefficient, vascular compliance, and the osmotic reflection coefficient were determined after the last hemodynamic mea...
Steffey EP, Woliner MJ, Dunlop C.Circulatory and respiratory effects of five h of constant 1.06 per cent alveolar halothane in oxygen were identified in eight healthy horses, which breathed spontaneously, were otherwise unmedicated and positioned in sternal recumbency. Only a few important significant (P less than 0.05) changes occurred with time. Total peripheral resistance was about 15 per cent lower after two hours of constant dose halothane than after 30 mins of constant dose (P less than 0.05) and accounted for the significant 10 per cent reduction in mean carotid arterial blood pressure. By 5 h, the reduction in resista...
Frank M, Weckman TJ, Wood T, Woods WE, Tai CL, Chang SL, Ewing A, Blake JW, Tobin T.Hordenine is an alkaloid occurring naturally in grains, sprouting barley, and certain grasses. It is occasionally found in post race urine samples, and therefore we investigated its pharmacological actions in the horse. Hordenine (2.0 mg/kg bodyweight [bwt]) was administered by rapid intravenous (iv) injection to 10 horses. Typically, dosed horses showed a flehmen response and defecated within 60 secs. All horses showed substantial respiratory distress. Respiratory rates increased about 250 per cent and heart rates were approximately double that of resting values. All animals broke out in a sw...
Valverde A, Boyd CJ, Dyson DH, Pascoe PJ.Dantrolene, a drug used in the prevention and treatment of malignant hyperthermia, was believed responsible for prolonged postanesthetic recumbency in a horse. Prophylactically, dantrolene was given orally before induction of anesthesia. Dantrolene has been recommended for use in horses at risk of developing postanesthetic myopathy. Side effects, including ataxia, may result from dantrolene administration.
Pereira A, Braekman JC, Dumont JE, Boeynaems JM.The incorporation of iodide into proteins (PBI) and lipids (LBI) of horse thyroid slices was measured in various conditions. Their dependency on the concentration of extracellular iodide was strikingly different. For PBI the relationship was biphasic with a decrease above 10 microM, likely to correspond to the Wolff-Chaikoff effect. On the contrary, LBI increased as a function of iodide concentration up to 100 microM. Methimazole (MMI) inhibited the incorporation of iodide into both LBI and PBI, but higher concentrations of MMI were required to depress LBI as compared to PBI. The inhibition of...
Houghton E, Dumasia MC, Teale P, Smith SJ, Cox J, Marshall D, Gower DB.Stable isotope gas chromatography/mass spectrometry has been used successfully in the elucidation of structures of urinary steroid metabolites in the horse and in the identification of metabolites isolated from in vivo perfusion and in vitro incubation studies using equine tissue preparations. Deuterium-labeled steroids, testosterone, dehydroepiandrosterone, and 5-androstene-3 beta,17 beta-diol have been synthesized by base-catalyzed isotope exchange methods and the products characterized by gas chromatography/mass spectrometry. [16,16(-2)H2]Dehydroepiandrosterone (plus radiolabeled dehydroepi...
Bochsler PN, Slauson DO, Neilsen NR.The essential role of the CD11/CD18 family of leukocyte adhesion molecules (LeuCams) in neutrophil-substrate adhesion is well documented. We have found that a monoclonal antibody designated 60.3 (MoAb 60.3) that recognizes the common beta-subunit (CD18) on human neutrophils (PMN) also recognizes a surface antigen on equine PMN. Antigen expression as assessed by immunofluorescence flow cytometry was enhanced by zymosan-activated serum (ZAS) or phorbol 12-myristate 13-acetate (PMA) stimulation. Pretreatment of equine PMN with MoAb 60.3 inhibited ZAS-stimulated aggregation, indicating that the mo...
D'Silva C.Equine liver glutathione S-transferase has been shown to consist of two identical subunits of apparent Mr 25,500 and a pl of 8.9. Kinetic data at pH 6.5 with 1-chloro-2,4-dinitrobenzene as a substrate suggests a random rapid-equilibrium mechanism, which is supported by inhibition studies using glutathione analogues. S-(p-Bromobenzyl)glutathione and the corresponding N alpha-, CGlu- and CGly-substituted derivatives have been found, at pH 6.5, to be linear competitive inhibitors, with respect to GSH, of glutathione transferase. N-Acetylation of S-(p-bromobenzyl)glutathione decreases binding by 1...
Foerster RJ, Wolf G.Equine blood polymorphonuclear leukocytes (PMN) were isolated by buffy coat and hypotonic lysis of residual erythrocytes. A highly reproducible method is described for measuring the uptake of opsonized latex microspheres by equine PMN using flowcytometry. The use of cytochalasin D allowed for differentiation of ingested from attached particles. The kinetics of phagocytosis in vitro is shown for different experimental conditions. We developed an assay for evaluation of phagocytic capacity of PMN which allows the assessment of drugs for their influence on phagocytosis in vivo as well as in vitro...
Baird AN, Scruggs DW, Watkins JP, Taylor TS.Sixteen horses were allotted to 4 groups of 4 horses each to evaluate the effect of tendon sheath lavage with 4 solutions (balanced electrolyte solution, 0.1% povidone-iodine, 0.5% povidone-iodine, and 0.5% chlorhexidine). The synovitis caused by 0.1% povidone-iodine lavage was not appreciably worse than that caused by balanced electrolyte solution lavage, but the 0.5% povidone-iodine and chlorhexidine lavages caused severe synovitis, and, therefore, should not be used for tendon sheath lavage.
Simon F, Laczay P, Móra Z, Lehel J.The target animal safety of a dexamethasone-prednisolone combination was studied on 12 horses divided into two groups of six each. One group of horses received the therapeutic dose of the combination (25 mg/animal dexamethasone pivalate and 75 mg/animal prednisolone) and the second group was given the threefold dose of it. The preparation was administered intravenously for 2 consecutive days. For assessment of safety a wide range of clinical, haematological, biochemical and urine variables were tested as laid down in the guidelines of the FDA. All horses treated by the therapeutic or the three...
Simoens P, Lauwers H, De Muelenare C, Muylle E, Steenhaut M.A clinical case of Horner's syndrome is described in a Standardbred horse, and the various symptoms of cranial sympathetic denervation are studied in two ponies after experimental transection of the left cervical sympathetic trunk and vagosympathetic trunk, respectively. The most prominent symptoms of equine Horner's syndrome were ptosis, local sweating and increased cutaneous temperature in the denervated area. Enophthalmos, miosis and increased lacrimation were also observed but these symptoms were mild, variable and difficult to ascertain. Prolapse of the third eyelid was not noticed. Conco...
Matthews NS, Lindsay SL.Minimum alveolar concentration (MAC) for halothane was measured before and after administration of intravenous butorphanol (0.022 and 0.044 mg/kg in bodyweight in nine yearling Shetland ponies. Arterial blood pressure, heart rate, respiratory rate, expired CO2 and rectal temperature was also measured. Even though mean MAC values decreased 10 and 9 per cent after the low and high doses respectively, they were not statistically different from those measured prior to butorphanol. Halothane MAC values increased after butorphanol in two ponies, both animals increasing locomotor activity and demonst...
Karcher LF, Dill SG, Anderson WI, King JM.Moderate to severe ulcerative colitis of the right dorsal colon was diagnosed by necropsy or by exploratory celiotomy and biopsy in 13 horses with a primary clinical complaint of either colic, diarrhea, or weight loss. Clinical signs varied from acute fulminating diarrhea (possibly with fever), colic, dehydration, endotoxic shock and death, to a chronic condition manifested by mild intermittent colic up to several months in duration, and weight loss with or without mild diarrhea. In a large percentage of the horses, those affected had been hypovolemic and received nonsteroidal anti-inflammator...
Gossett KA, French DD, Cleghorn B, Church GE.Hypertonic NaHCO3 infusion caused blood volume expansion, increased blood bicarbonate concentration, and delayed the onset of hypophosphatemia in ponies with endotoxemia. However, NaHCO3 infusion did not normalize blood pH, and it increased blood L-lactate concentration, and caused hypokalemia, hypernatremia, and hyperosmolality. The deleterious effects of NaHCO3 infusion in endotoxemia ponies outweighed the beneficial effects. The role of hypertonic NaHCO3 given IV for treatment of endotoxemia in equids must be reevaluated.
Linden A, Art T, Amory H, Desmecht D, Lekeux P.Seven sport horses were investigated to compare physiological and pharmacological stresses on the plasma glucocorticosteroid levels. Venous blood was sampled and analysed for cortisol concentrations before and after each type of stress. The physiological stress was induced by the completion of a cross-country and the pharmacological one, by an intravenous ACTH administration (200 micrograms) in the same horses, one week after the course. Both exercise and ACTH injection induced a highly significant cortisol increase of 79 +/- 0.10% and 160 +/- 0.18%, respectively. The relative plasma cortisol ...
Naidoo V, Gehring R.An overview of reports of suspected adverse drug reactions received by the Veterinary Pharmacovigilance and Medicines Information Centre during the period March 2001 to February 2002 is given. A total of 77 reports were received. The majority of reports involved suspected adverse reactions that occurred in dogs and cats. Most products implicated in the reports were Stock Remedies. The products were predominantly administered either by veterinarians or trained paraveterinary professionals. Although the majority of reports were received from veterinary pharmaceutical companies, the proportion of...
Grandy JL, Hodgson DS, Dunlop CI, Chapman PL, Heath RB.The cardiopulmonary effects of intravenous (i.v.) administration of the sympathomimetic drug ephedrine during two different levels of halothane anesthesia [end-tidal concentration of 1.37% (light anesthesia) and 2.1% (deep anesthesia)] were studied in eight horses. Anesthesia was induced and maintained using only halothane in O2. Ventilation was controlled to maintain a Paco2 of 38-42 mmHg. Following instrumentation and stabilization of the horse at the halothane concentration being studied, baseline measurements of cardiac output (Q), arterial blood pressure (AP), pulmonary artery pressure, h...
Decloedt A, Damen S, Vanhaecke L.Anabolic-androgenic steroids (AAS) are strictly forbidden in equine sports because of their stimulating effect on muscle growth and performance. Nevertheless, low levels of AAS have been found in some horses, untreated with AAS. Glucocorticoids (GC), used as an anti-inflammatory therapy and structurally related to AAS, might play a role in this phenomenon. In order to unravel this possible correlation the influence of glucocorticoid treatment on the excretion of AAS was studied both in vivo and in vitro. In vivo effects were investigated by analysing urine samples collected from a gelding trea...
Hansson E, Skiöldebrand E.To treat osteoarthritic chondrocytes and thereby reduce the inflammation with a drug combination that primarily affects 5-HT- and ATP-evoked Ca2+ signaling. In osteoarthritic chondrocytes, Ca2+ signaling is elevated, resulting in increased production of ATP and inflammatory mediators. The expression of TLR4 and Na+/K+-ATPase was used to evaluate the inflammatory status of the cells. Methods: Equine chondrocytes were collected from joints with mild structural osteoarthritic changes and cultured in monolayers. The cells were treated with a combination of bupivacaine (1 pM) and sildenafil (1 ...
Jaramillo FM, Piñeros DDV, Corrêa RR, Pogliani FC, Cogliati B, Baccarin RYA.Despite hepatotoxic effects, imidocarb dipropionate is the drug of choice for treatment of equine piroplasmosis. It is important, therefore, to identify adjuvant therapies that may improve the safety of imidocarb dipropionate by reducing the risk of liver damage during its use. The aim of the present study was to evaluate the hepatoprotective and hepatoregulatory effects of treatment with and during administration of imidocarb dipropionate. Methods: Ten healthy horses, seroconverted to by C-ELISA, were treated with 5 mg/kg/day of imidocarb dipropionate for three consecutive days. The study ...
Black JB, Frampton AR.Equine herpesvirus type 1 (EHV-1) is a highly transmissible pathogen that leads to a variety of clinical disease outcomes in infected horses. A major sequela that can occur after an EHV-1 infection is a neurological disease termed equine herpesvirus myeloencephalopathy (EHM). Clinical manifestations of EHM include fever, ataxia, incontinence, and partial to full paralysis, which may ultimately lead to the euthanization of the infected horse. To develop an effective treatment strategy for EHM, it is critical that the specific virus-host interactions that lead to EHM be investigated so that safe...
Ijpma G, Liang CQ, Kachmar L, Panariti A, Benedetti A, Lavoie JP, Lauzon AM.Isolated human airway smooth muscle (ASM) tissue contractility studies are essential for understanding the role of ASM in respiratory disease, but limited availability and cost render storage options necessary for optimal use. However, to our knowledge, no comprehensive study of cryopreservation protocols for isolated ASM has been performed to date. We tested several cryostorage protocols on equine trachealis ASM using different cryostorage media [1.8 M dimethyl sulfoxide and fetal bovine serum (FBS) or Krebs-Henseleit (KH)] and different degrees of dissection (with or without epithelium and c...
Anderson F.With the approach of the menopause and the cessation of ovarian estrogen production, a number of uncomfortable and/or dangerous conditions may be manifested, and are all indications for estrogen replacement therapy. Various routes of estrogen administration are available--oral, subcutaneous implant, intravaginal, and transdermal--each having advantages and disadvantages. There is also a choice possible among replacement hormones, which include the natural estrogens, such as estradiol and estropipate; synthetic estrogens, for example, ethinyl estradiol and diethylstilbestrol; and conjugated equ...
Asmis R, Jörg A.Horse eosinophils preincubated with 3H-labelled acetate and stimulated with the Ca2+ ionophores ionomycin or A23187 form a radioactive compound, which we have shown to be 1-O-alkyl-2-[3H]acetyl-sn-glycero-3-phosphocholine (platelet-activating factor). We could detect no 1-O-acyl-2-[3H]acetyl-glycero-3-phosphocholine in the radioactive fraction. The formation of platelet-activating factor was strongly correlated to the generation of leukotriene C4, the main arachidonate metabolite in horse eosinophils, suggesting that platelet-activating factor and leukotriene C4 have a common precursor pool (1...
True RG, Lowe JE.Juglone, a toxic compound found in all parts of plants of the walnut tree family Jugans, was evaluated as the possible toxin involved in black walnut shaving-associated laminitis in the horse. Large amounts (up to 1 g) of this chemical administered per os inconsistently caused mild signs of laminitis in ponies. Topical application of juglone to the digits of horses caused local skin irritation but did not cause laminitis. Intravenous administration of juglone caused acute pulmonary edema in some individuals previously exposed to the compound per os or IV.
Csik-Salmon J, Blais D, Vaillancourt D, Garon O, Bisaillon A.Loss of rear motor control is the main limiting factor in the use of caudal epidural anesthesia in the horse. In man and laboratory animals, a small dose of an opiate combined with a local anesthetic enhances analgesia without impairing motor function. Thus, the amount of local anesthetic administered may be reduced. Butorphanol is an opiate widely used in horses. It has a good margin of safety and few cardiorespiratory effects. The effects of lidocaine (0.25 mg/kg) and lidocaine-butorphanol (0.25 mg/kg, and 0.04 mg/kg, respectively) were compared in 2 groups of 5 healthy unsedated mares. Hors...
Boyd EH, Allen WE.Plasma drug concentrations were measured after two commercially available potentiated sulphonamides, trimethoprim and sulfadoxine and trimethoprim and sulphadiazine, were infused daily for 2 and 3 days, respectively, into the uteri of pony mares which had been mated before ovulation. Intravenous administration of trimethoprim and sulfadoxine allowed uterine absorption of trimethoprim (23-43%) and sulfadoxine (29-34%) to be calculated. After intra-uterine administration trimethoprim and sulphadiazine were detected in the milk of a lactating mare. In order to maintain plasma concentrations likel...
Rojas G, Vargas M, Robles A, Gutiérrez JM.Twenty batches of polyvalent antivenom produced at the Instituto Clodomiro Picado were analyzed for turbidity, both before and after freezing-thawing and lyophilization. Eight batches became turbid upon freezing-thawing, and this change correlated with high levels of cholesterol, triglycerides and lipoproteins, especially beta-lipoprotein. Since normal horse serum does not become turbid after freezing-thawing, despite the fact that it has high lipoprotein levels, the possibility was raised that phenol, used as a preservative during serum fractionation, might affect lipoproteins, inducing the a...
Allen GP, Cohen JC, Randall CC, O'Callaghan DJ.The replication of equine herpesvirus type 1 (EHV-1) and type 3 (EHV-3) was unimpeded in three different cell types-equine epithelial cells, equine fibroblasts, and mouse fibroblasts-which had been blocked in their capacity to synthesize host DNA by 2.5 mM hydroxyurea (HU) or 2 mM thymidine (TdR). The rate of DNA synthesis in uninfected or equine herpesvirus-infected cells in the presence of HU or TdR was measured by pulse-labeling cell samples with a labeled DNA precursor at different times after infection. DNA synthesis in uninfected cultures was completely inhibited by both compounds. Howev...
Baxter GM, Tackett RL, Moore JN.Palmar digital arteries and veins removed surgically from healthy horses under general anesthesia were cut into 4 mm vascular rings, suspended in tissue baths, and attached to force displacement transducers for continuous measurement of vascular tension. In vitro vascular responses were determined for acetylcholine, acepromazine, isoxsuprine hydrochloride (isoxsuprine), prostaglandin E2 (PGE2), and prostaglandin I2 (prostacyclin). After preconstriction with norepinephrine hydrochloride (norepinephrine), or prostaglandin F2 alpha (PGF2 alpha), the concentrations needed to produce 50% maximum re...
Fultz LE, Peloso JG, Giguère S, Adams AR.To compare the outcome of horses with nephrosplenic entrapment of the large colon (NSELC) that were treated nonsurgically by IV administration of phenylephrine and exercise with that of horses treated by IV administration of phenylephrine and a rolling procedure under general anesthesia. Methods: Retrospective case series. Methods: 88 horses with NSELC. Methods: Horses examined between 2004 and 2010 because of acute abdominal pain that had NSELC on the basis of findings on abdominal palpation per rectum, abdominal ultrasonography, or both were included. Medical records were reviewed to obtain ...
Müller T, Chavaillaz PA, Jörg A, Grob M, Peterhans E.It was shown in several cell types that the dual lipoxygenase and cyclooxygenase inhibitor eicosatetraynoic acid but not the cyclooxygenase inhibitor acetylsalicylic acid suppressed luminol-dependent chemiluminescence. Since lipoxygenase is known to generate chemiluminescence in vitro, these observations were interpreted as evidence for a direct contribution of the lipoxygenase pathway to light emission in intact cells. We have investigated a possible contribution of the lipoxygenase to the chemiluminescence of horse eosinophils by directly comparing the formation of the byproduct chemilumines...
Olson LE, Perkowski SZ, Mason DE, Muir WW.Strips of trachealis muscle were dissected from the mid-cervical portion of the trachea from horses that were free of respiratory tract disease. The epithelium and mucosa were removed from one group of tissues and were left intact in a second group of tissues. Each tissue was suspended in a bath filled with Krebs-bicarbonate solution that was aerated with 5% CO2 in oxygen and maintained at 37 degrees C. Isometric tension was continuously recorded. The contractile response to square-wave electrical stimulations increased as frequency (3, 5, 10, 15, 20, 25, and 30 Hz), voltage (10, 15, 18, and 2...
Tulamo RM, Raekallio M, Taylor P, Johnson CB, Salonen M.Both morphine and physiologic saline injected intra-articularly into healthy equine tarsocrural joints induced a release of large molecular size proteoglycan (PG) subunits into the synovial fluid (SF) analysed 24 h postinjection. High-performance liquid chromatography (HPLC) with a size-exclusion column was used to assess the high molecular weight proteoglycans in equine synovial fluid (SF). The PG peaks of SF samples eluated separately from SF hyaluronate and other molecular components of the SF in the HPLC chromatographies indicating no interaction between hyaluronate and PG in the SF. Indiv...
Wang Z, Yu M, Robinson NE, Broadstone RV, LeBlanc PH, Derksen FJ.The modulatory role of prostaglandin E2 (PGE2) was examined in pony tracheal smooth muscle strips. Although exogenous PGE2 inhibited the contractile response to both electrical field stimulation (EFS) and acetylcholine (ACh) in a dose-dependent manner, the concentration required to inhibit the response to EFS (10 nM) was less than that required to inhibit the response to ACh (0.1 microM). Cyclooxygenase inhibition with aspirin or meclofenamate had no effect on either the response to EFS or to ACh even though PGE2 production was inhibited. Our results demonstrate that in ponies as in other spec...
Tung JT, Venta PJ, Eberhart SW, Yuzbasiyan-Gurkan V, Alexander L, Caron JP.To determine the effects of recombinant equine interleukin -1beta (reIL-1beta) and 4 anti-inflammatory compounds on the expression and activity of cyclooxygenase (COX)-2 in cultured equine chondrocytes. Methods: Articular cartilage from 9 young adult horses. Methods: Reverse transcriptase-polymerase chain reaction methods were used to amplify a portion of equine COX-2 to prepare a cDNA probe. Northern blot analysis was used to quantify the expression of COX-2 in first-passage cultures of equine articular chondrocytes propagated in media containing dexamethasone (DEX), phenylbutazone (PBZ), pol...
Poole AW, Heath MF, Evans RJ.Pre-incubation of equine platelets in platelet-rich plasma with adenosine 5'-diphosphate (ADP) induced a reduction in aggregation responsiveness to subsequent additions of ADP. The desensitisation was shown to be homologous since the responsiveness to platelet-activating factor, thrombin, collagen, 5-hydroxytryptamine or ionomycin remained unchanged. Adenosine 5'-(beta-thio)-diphosphate (ADP beta S), a non-hydrolysable analogue of ADP, was shown to act as an agonist inducing aggregation by interaction with the ADP receptor. ADP beta S was then used in the desensitisation studies in which resid...
Beasley AM, Coleman GT, Kotze AC.The use of macrocyclic lactone drugs for control of equine cyathostomins is threatened by increasing levels of resistance. Detection of changes in drug sensitivity is important for effective and sustainable management of cyathostomins, however, at present such detection relies on the use of the faecal egg count reduction test, which is known to be an insensitive method. The present study therefore aimed to examine the use of a 96-well plate larval migration inhibition test for detection of resistance to macrocyclic lactone drugs in cyathostomins. We optimised conditions for migration of larvae...
Wong AS, Ho EN, Wan TS.Myo-inositol trispyrophosphate (ITPP) is a new drug capable of increasing the amount of oxygen in hypoxic tissues. Studies have shown that administration of ITPP increases the maximal exercise capacity in normal mice as well as mice with severe heart failure. The properties of ITPP make it an ideal candidate as a doping agent to enhance performance in racehorses. While there have been speculations in the horseracing industry that the covert use of ITPP is already widespread, no reported method exists for the detection of ITPP in equine biological samples. ITPP is a difficult-to-detect drug due...
Stein F, Gilliam L, Davis J, Taylor J.In a randomized crossover design study, 10 adult horses were administered crushed metronidazole tablets rectally at 20 mg/kg. Horses' rectums were either evacuated (E) or not evacuated (NE) of manure prior to the administration of the drug. Serum samples were taken over 24 hr and plasma concentrations were determined via high pressure liquid chromatography. At 15 min post-administration, group E had a significantly higher plasma concentration (p = 0.027), but there were no concentration differences at any other time points. There was large variability in relative bioavailability in the NE...
McCandless EE, Rai SK, Mwangi D, Sly L, Franz LC.Hydrocortisone is widely accepted as an anti-inflammatory agent and there are many products available containing hydrocortisone as an active ingredient. Surprisingly, there is little data available specifically on the immunological effects of hydrocortisone in large animals. Glucocorticoids are well-characterized for their ability to repress inflammation via a wide variety of mechanisms including suppression of cytokine production. In this study the effects of hydrocortisone on IFN-γ production by equine, bovine, and ovine PBMCs were assessed using flow cytometric or ELISpot analysis. Hydroco...
Freeman DE, Ferrante PL, Palmer JE.A Latin square design was used to compare the effects of laxatives and a corresponding volume of water on gastrointestinal tract function in 4 healthy horses. Horses were intragastrically infused with each of the following: dioctyl sodium sulfosuccinate (DSS; 50 mg/kg of body weight); magnesium sulfate (0.5 g/kg--low dosage); magnesium sulfate (1.0 g/kg--high dosage); and an equal volume of water (6 L) given as a control infusion. From 5 to 33 hours after the high dosage of magnesium sulfate, feces were slightly softer than usual in all horses. In 1 horse, DSS caused mild colic, hyperpnea, and...
Moffatt RE, Kramer LL, Lerner D, Jones R.Concentrations of dioctyl sodium sulfosuccinate (DSS) ranging from three to five times the recommended dosage produced severe diarrhea, rapid dehydration and death in seven horses and 66 guinea pigs when administered experimentally per os. Clinicopathological findings indicated hemoconcentration in both horses and guinea pigs. There was a leucocytosis in the guinea pigs given the highest dosages. In all cases the principal finding at necropsy was extreme fluid distention of the intestinal tract. There was histopathological evidence of epithelial denudation and vascular stasis. The LD50 in the ...
Parra N, Jaume M, Boscán K, Hernández A, Mijares A, González M, Alvarado Y, Restrepo J.Trypanosoma equiperdum is the causative agent of dourine, a venereal disease in horses and donkeys. This parasite has a widely distribution, is found in Africa, Asia, Southern and Eastern Europe, Russia, Mexico and Venezuela. The T. equiperdum is morphologically indistinguishable to other Trypanozoon species, however differs from other mammalian trypanosomes due to the fact that it is primarily a tissue parasite, generating cutaneous plaques, swelling of genitalia and neurological signs. The aim of this study was to evaluate the trypanocidal effectiveness of a set of derivatives of thiosemicar...
French DD, Klei TR, Taylor HW, Chapman MR, Wright FR.The efficacy of ivermectin in oral paste formulation at a dosage of 200 micrograms/kg of body weight was tested against naturally acquired larval and adult stages of Parascaris equorum, in a controlled study. Twenty infected pony foals 18 to 27 weeks of age were randomly allocated to 2 groups of 10 each and were placed in dry lots. Foals in 1 group were given ivermectin on day 0. Necropsies and parasite recoveries from small intestines and lung tissues were performed on 5 foals in each group at 2 weeks after treatment (WAT) and on the remaining foals at 5 WAT. Ivermectin was 100% effective aga...
