Inducible nitric oxide expression in equine articular chondrocytes: effects of antiinflammatory compounds

OBJECTIVE

To determine the effects of recombinant equine IL-1beta and a number of antiinflammatory compounds on the expression and activity of inducible nitric oxide synthase (iNOS) in cultured equine chondrocytes.

DESIGN

RT-PCR methods were used to amplify a portion of the equine iNOS message to prepare an RNA probe. Northern blot analysis was used to quantify the expression of iNOS in first passage cultures of equine articular chondrocytes propagated in the presence or absence of recombinant equine interleukin-1beta (reIL-1beta), dexamethasone (DEX), polysulfated glycosaminoglycan (PSGAG), hyaluronan (HA), and phenylbutazone (PBZ), each at concentrations of 10 and 100 microg/ml. Nitrite concentrations in conditioned media of similarly treated cells were used to quantify iNOS activity.

RESULTS

Recombinant equine IL-1beta increased the expression of iNOS in a dose-dependent manner. This result was paralleled by an increased concentration of nitrite in the culture media of reIL-1beta-treated cells. DEX and PSGAG significantly reduced iNOS gene expression and media supernatant nitrite concentrations in cytokine-stimulated cultures. HA and PBZ had no consistent effect on the expression of iNOS and did not significantly influence nitrite content of conditioned media.

CONCLUSIONS

NO is considered an important mediator in the pathophysiologic processes of arthritis and an inducible NOS is expressed by equine chondrocytes. Pre-translational regulation of the iNOS gene by DEX and PSGAG appears to contribute to the cartilage-sparing properties of these compounds.

Effects of oral administration of phenylbutazone to horses on in vitro articular cartilage metabolism

OBJECTIVE

To evaluate the effects of orally administered phenylbutazone on proteoglycan synthesis and chondrocyte inhibition by IL-1beta in articular cartilage explants of horses.

ANIMALS

11 healthy 1- to 2-year-old horses.

PROCEDURE

Horses were randomly assigned to the control (n = 5) or treated group (4.4 mg of phenylbutazone/kg of body weight, p.o., q 12 h; n = 6). Articular cartilage specimens were collected before treatment was initiated (day 0), after 14 days of treatment, and 2 weeks after cessation of treatment (day 30). Proteoglycan synthesis and stromelysin concentration in cartilage extracts were assessed after 72 hours of culture in medium alone or with recombinant human interleukin-1beta (IL-1beta; 0.1 ng/ml).

RESULTS

On day 0, proteoglycan synthesis was significantly less in cartilage explants cultured in IL-1beta, compared with medium alone. Mean proteoglycan synthesis in explants collected on days 14 and 30 was significantly less in treated horses, compared with controls. However, incubation of explants from treated horses with IL-1beta did not result in a further decrease in proteoglycan synthesis. Significant differences in stromelysin concentration were not detected between or within groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Oral administration of phenylbutazone for 14 days significantly decreased proteoglycan synthesis in articular culture explants from healthy horses to a degree similar to that induced by in vitro exposure to IL-1beta. Phenylbutazone should be used judiciously in athletic horses with osteoarthritis, because chronic administration may suppress proteoglycan synthesis and potentiate cartilage damage.

In vitro effects of cyclooxygenase inhibitors in whole blood of horses, dogs, and cats

OBJECTIVE

To determine potency and selectivity of nonsteroidal anti-inflammatory drugs (NSAID) and cyclooxygenase- (COX-) specific inhibitors in whole blood from horses, dogs, and cats.

SAMPLE POPULATION

Blood samples from 30 healthy horses, 48 healthy dogs, and 9 healthy cats.

PROCEDURE

Activities of COX-1 and COX-2 were determined by measuring coagulation-induced thromboxane and lipopolysaccharide-induced prostaglandin E2 concentrations, respectively, in whole blood with and without the addition of various concentrations of phenylbutazone, flunixin meglumine, ketoprofen, diclofenac, indomethacin, meloxicam, carprofen, 5-bromo-2[4-fluorophenyl]-3-14-methylsulfonylphenyl]-thiophene (DuP 697), 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl) phenyl-2(5H)-furan one (DFU), 3-(3,4-difluorophenyl)-4-(4-(methylsulfonyl)phenyl)-2-(5H)-furanone (MF-tricyclic), and celecoxib. Potency of each test compound was determined by calculating the concentration that resulted in inhibition of 50% of COX activity (IC50). Selectivity was determined by calculating the ratio of IC50 for COX-1 to IC50 for COX-2 (COX-1/COX-2 ratio).

RESULTS

The novel compound DFU was the most selective COX-2 inhibitor in equine, canine, and feline blood; COX-1/COX-2 ratios were 775, 74, and 69, respectively. Carprofen was the weakest inhibitor of COX-2, compared with the other COX-2 selective inhibitors, and did not inhibit COX-2 activity in equine blood. In contrast, NSAID such as phenylbutazone and flunixin meglumine were more potent inhibitors of COX-1 than COX-2 in canine and equine blood.

CONCLUSIONS AND CLINICAL RELEVANCE

The novel COX-2 inhibitor DFU was more potent and selective in canine, equine, and feline blood, compared with phenylbutazone, flunixin meglumine, and carprofen. Compounds that specifically inhibit COX-2 may result in a lower incidence of adverse effects, compared with NSAID, when administered at therapeutic dosages to horses, dogs, and cats.

[Effect of anti-inflammatory drugs, alone and combined with ofloxacin, on the respiratory burst of human polymorphonuclear leukocytes]

The antibacterial activity of polymorphonuclear leukocytes (PMNs) is based on the production of superoxide anion and H(2)O(2) in the respiratory burst and can be impaired in different ways. The combination of an antibacterial agent and an antiinflammatory drug is quite common in immunodepressed patients whose respiratory burst of PMN could be impaired. In this study we examine in vitro the effect of pretreating (35 degrees C for 30 min) PMNs with the antiinflammatory drugs dexamethasone (0.4, 4 and 40 microgram/ml), methylprednisolone (0.37, 3.7 and 37 microgram/ ml), hydrocortisone (0.048, 0.48 and 4.8 microgram/ml), betamethasone (0.1, 1, 5 and 10 mg/ml), phenylbutazone (1000 microgram/ml) and acetylsalicylic acid (25, 250, 2500 microgram/ml) alone, and combined with 10 mg/ml of ofloxacin on the respiratory burst. Superoxide anion was measured by the cytochrome c reduction microtechnique and H(2)O(2) by phenol red. The antiinflammatory drugs alone decreased the production of H(2)O(2) (except dexamethasone and methylprednisolone) and superoxide anion (except betamethasone) from 15-45%, depending on the antiinflammatory drug and concentration, while ofloxacin increased the production of superoxide anion (20.2 +/- 6.7%). The combination of antiinflammatory drugs with ofloxacin neutralizes the inhibitory effect of the former on the respiratory burst of PMNs. It is therefore important to know the effect of drugs on the respiratory burst in order to choose those that have the same therapeutic effect without interfering with PMN functions.

Cytotoxicity and mode of action of 1-(1-cyclohexenyl) and 1-unsubstituted 3,5-pyrazolidinediones in human Molt4 T cell leukemia

The 3,5-pyrazolidinediones proved to be potent cytotoxic agents against the growth of a number of murine and human tumor cell lines, e.g. human THP-I monocytic leukemia, Hut-78 lymphoma, MCF-7 breast effusion, A549 lung carcinoma, U87MG glioma, Hela uterine and A431 epidermoid skin cancer. In human Tmolt4 cell leukemia, the agents substantially suppressed DNA and RNA syntheses after 60 min at 100 microM. The de novo purine biosynthetic pathway appeared to be the major target of the agents with the inhibition of both PRPP-amido transferase and IMP dehydrogenase (IMPDH) activities. Suppression of IMPDH activity was due to the inhibition of both the Type I and II isoforms through an uncompetitive mechanism; however, the Type II isoform was preferentially inhibited at lower concentrations of compounds tested (>50-150 microM). Therefore IMPDH Type II activity, which predominates in cancer cells, was selectively inhibited over the Type I isoform (208-312 microM). The activities of other enzymes examined were inhibited which added to the overall suppression of DNA synthesis, i.e., ribonucleotide reductase, dihydrofolate reductase and nucleoside kinases. The agents caused Tmolt4 DNA strand scission but the DNA molecule itself did not appear to be a target of the compounds since there was no induced cross-linking of the DNA, intercalation between base pairs or alkylation of the DNA bases.

Identification and reactivity of the major metabolite (beta-1-glucuronide) of the anti-tumour agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) in humans

1. The novel anti-tumour agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is extensively metabolized by glucuronidation and 6-methylhydroxylation, resulting in DMXAA acyl glucuronide (DMXAA-G) and 6-hydroxymethyl-5-methylxanthenone-4-acetic acid (6-OH-MXAA). 2. The major human urinary metabolite of DMXAA was isolated and purified by a solid-phase extraction (SPE) method. The isolated metabolite was hydrolysed to free DMXAA by strong base, and by beta-glucuronidase. Liquid chromatography-mass spectrometry (LC-MS) and spectral data indicated the presence of a molecular ion [M + 1]+ at m/z 459, which was consistent with the molecular weight of protonated DMXAA-G. 3. The glucuronide was unstable in buffer at physiological pH, plasma and blood with species variability in half-life. Hydrolysis and intramolecular migration were major degradation pathways. 4. In vitro and in vivo formation of DMXAA-protein adducts was observed. The formation of DMXAA-protein adducts in cancer patients receiving DMXAA was significantly correlated with plasma DMXAA-G concentration and maximum plasma DMXAA concentration. 5. At least five metabolites of DMXAA were observed in patient urine, with up to 60% of the total dose excreted as DMXAA-G, 5.5% as 6-OH-MXAA and 4.5% as the glucuronide of 6-OH-MXAA. 6. These data suggest that the major metabolite in patients' urine is DMXAA beta-1-glucuronide, which may undergo hydrolysis, molecular rearrangement and covalent binding to plasma protein. The reactive properties of DMXAA-G may have important implications for the pharmacokinetics, pharmacodynamics and toxicity of DMXAA.

Phenylbutazone radicals inactivate creatine kinase

Creatine kinase (CK) was used as a marker molecule to examine the side effect of damage to tissues by phenylbutazone (PB), an effective drug to treat rheumatic and arthritic diseases, with horseradish peroxidase and hydrogen peroxide (HRP-H(2)O2). PB inactivated CK during its interaction with HRP-H(2) O(2), and inactivated CK in rat heart homogenate. PB carbon-centered radicals were formed during the interaction of PB with HRP-H(2)O2. The CK efficiently reduced electron spin resonance signals of the PB carbon-centered radicals. The spin trap agent 2-methyl-2-nitrosopropane strongly prevented CK inactivation. These results show that CK was inactivated through interaction with PB carbon-centered radicals. Sulfhydryl groups and tryptophan residues in CK were lost during the interaction of PB with HRP-H(2)O2, suggesting that cysteine and tryptophan residues are oxidized by PB carbon-centered radicals. Other enzymes, including alcohol dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, but not lactate dehydrogenase, were also inactivated. Sulfhydryl enzymes seem to be sensitive to attack by PB carbon-centered radicals. Inhibition of SH enzymes may explain some of the deleterious effects induced by PB.

Synthesis and anti-inflammatory activity of 1-acetyl-5-substituted aryl-3-(beta-aminonaphthyl)-2-pyrazolines and beta-(substituted aminoethyl) amidonaphthalenes

The title compounds were prepared by reaction of beta-acetylamino-naphthalene with different aromatic aldehydes followed by cyclisation with hydrazine hydrate and with different primary or secondary amines (Mannich's reaction), respectively. The structures of new compounds were confirmed by 1H-NMR and IR spectral data. Anti-inflammatory and ulcerogenic activities in vivo were evaluated and compared with the standard drugs, phenylbutazone and indomethacin. Some compounds of the series exhibited promising anti-inflammatory activity with a lower ulcerogenic liability than the standard drugs.

Effects of anti-inflammatory drugs on lipopolysaccharide-challenged and -unchallenged equine synovial explants

OBJECTIVE

To evaluate the effects of anti-inflammatory drugs on lipopolysaccharide (LPS)-challenged and -unchallenged equine synovial membrane in terms of production of prostaglandin E2 (PGE2) and hyaluronan, viability, and histomorphologic characteristics.

SAMPLE POPULATION

Synovial membranes were collected from the carpal, tarsocrural, and femoropatellar joints of 6 adult horses.

PROCEDURE

Synovial membranes from each horse were minced and pooled and explants were treated with one of the following: no drug (control), drug, LPS alone, or LPS and drug. Treatment drugs were phenylbutazone (PBZ), flunixin meglumine (FNX), ketoprofen (KET), carprofen (CRP), meloxicam (MEL), low-concentration methylprednisolone (METH), high-concentration METH, dimethyl sulfoxide (DMSO), or an experimental COX-2 inhibitor (dissolved in DMSO). Following 48 hours of culture, medium was assayed for PGE2 and hyaluronan concentration. Synovial explants were assessed for viability and histomorphologic characteristics.

RESULTS

For the LPS-challenged explants, PBZ, FNX, KTP CRF MEL, and low-concentration METH suppressed PGE2 production, compared with LPS challenge alone. Only MEL suppressed PGE2 production from LPS-challenged explants, compared with unchallenged explants. Synovial explants maintained > 90% viability and there was no significant difference in viability or hyaluronan production among explants. Histomorphologic scores were significantly decreased for explants treated with low-concentration METH or DMSO.

CONCLUSIONS AND CLINICAL RELEVANCE

PBZ, FNX, KTP, CRFP MEL, and low-concentration METH suppressed PGE2 production in LPS-challenged explants. Meloxicam appeared to have more selective suppression of COX-2 activity. Histomorphologic scores suggest detrimental effects of METH, DMSO, and the experimental COX-2 inhibitor. Commonly used nonsteroidal anti-inflammatory drugs suppress induced synovial membrane PGE2 production without detrimental effects on synovial membrane viability and function.

Anti-inflammatory activity of Pothomorphe peltata leaf methanol extract

The methanol extract of Pothomorphe peltata leaves, orally administered at the dose of 20 mg/kg (equivalent to 2.50 g dry plant/kg) body weight, exhibited a significant anti-inflammatory activity, comparable with phenylbutazone (80 mg/kg, p.o.), against adjuvant-carrageenan-induced edema in rats.

Anti-inflammatory evaluation of Ficus racemosa Linn. leaf extract

The anti-inflammatory activity of Ficus racemosa extract was evaluated on carrageenin, serotonin, histamine and dextran-induced rat hind paw oedema models. The extract at doses of 200 and 400 mg/kg has been found to possess significant anti-inflammatory activity on the tested experimental models. The extract (400 mg/kg) exhibited maximum anti-inflammatory effect, that is 30.4, 32.2, 33.9 and 32.0% at the end of 3 h with carrageenin, serotonin, histamine, dextran-induced rat paw oedema, respectively. In a chronic test the extract (400 mg/kg) showed 41.5% reduction in granuloma weight. The effect produced by the extract was comparable to that of phenylbutazone, a prototype of a non-steroidal anti-inflammatory agent.

Effects of phenylbutazone on bone activity and formation in horses

OBJECTIVE

To determine the effects of phenylbutazone (PBZ) on bone activity and bone formation in horses.

ANIMALS

12 healthy 1- to 2-year-old horses.

PROCEDURES

Biopsy was performed to obtain unicortical bone specimens from 1 tibia on day 0 and from the contralateral tibia on day 14. Fluorochromic markers were administered IV 2 days prior to and on days 0, 10, 15, and 25 after biopsy was performed. Six horses received PBZ (4.4 mg/kg of body weight, PO, q 12 h) and 6 horses were used as controls. All horses were euthanatized on day 30 and tissues from biopsy sites, with adjacent cortical bone, were collected. Osteonal density and activity, mineral apposition rate (MAR), and percentage of mineralized tissue filling the biopsy-induced defects in cortical bone were assessed. Serum samples from all horses were analyzed for bone-specific alkaline phosphatase activity and concentration of PBZ.

RESULTS

MAR was significantly decreased in horses treated with PBZ. Regional acceleratory phenomenon was observed in cortical bone in both groups but was significantly decreased in horses treated with PBZ. Osteonal activity was similar at all time points in all horses. In control horses, percentage of mineralized tissue filling the cortical defects was significantly greater in defects present for 30 days, compared with defects present for 14 days. Differences in percentage of mineralized tissue were not detected in horses treated with PBZ.

CONCLUSIONS AND CLINICAL RELEVANCE

PBZ decreased MAR in cortical bone and appeared to decrease healing rate of cortical defects in horses.

Binding of kebuzone to human serum albumin studied by high performance liquid affinity chromatography

The binding of the anti-inflammatory agent kebuzone (CAS 853-34-9) to human serum albumin (HSA) was examined by means of high performance liquid affinity chromatography. Phenylbutazone and diazepam, the binding properties of which were an object of our previous work, were used as markers for the major supposed binding sites on HSA. It was established that kebuzone binds to the high-affinity phenylbutazone binding sites as well as to the low-affinity diazepam binding sites. The estimated values of the equilibrium affinity constants were 5.9 x 10(4) l/mol and 1.7 x 10(3) l/mol, respectively, suggesting a low binding affinity for kebuzone. A stepwise mechanism of the binding process could be proposed: primary at phenylbutazone sites, and secondary at the diazepam sites. The binding behavior of kebuzone was very similar to that of the structurally related compound phenylbutazone. The observed lower affinity is well explained in view of the lower lipophilicity of kebuzone.

In vitro effects of nonsteroidal anti-inflammatory agents and prostaglandins I2, E2, and F2alpha on contractility of taenia of the large colon of horses

OBJECTIVES

To determine the in vitro effect of various prostaglandins (PG) and nonsteroidal anti-inflammatory drugs (NSAID) on contractile activity of the large-colon taenia of horses.

ANIMALS

14 healthy horses.

PROCEDURE

The taenia was collected from the ventral colon, cut into strips (2 X 10 mm), and mounted in a tissue bath system (20-ml capacity) that contained oxygenated Krebs buffer solution warmed to 37.5+/-0.5 C. After equilibration, incremental doses of PGE2, PGF2alpha, PGl2, flunixin meglumine, carprofen, ketoprofen, and phenylbutazone were added to the baths, and contractile activity was recorded. Magnitude of the response was calculated by comparing contractile activity before and after administration of the PG or NSAID to the tissue baths.

RESULTS

PGE2 and PGF2alpha, caused a significant increase in contractile activity, whereas PGI2 induced an inhibitory response. Activity of NSAID on contraction was predominantly inhibitory. At low concentrations, ketoprofen induced an excitatory effect, which then became inhibitory at high concentrations. Compared with the other NSAID, carprofen significantly reduced contractile activity at lower concentrations.

CONCLUSIONS

PGE2 and PGF2alpha appear to enhance contractility of large-colon taenia of horses, whereas PGI2 was inhibitory in the in vitro model. Administration of NSAID also inhibited contractility, with carprofen having the most potent effect.

CLINICAL RELEVANCE

Administration of NSAID in combination with liberation of endogenous PG may predispose horses to development of intestinal stasis and subsequent impaction.

Attenuation by phenylbutazone of the renal effects and excretion of frusemide in horses

The objectives of this study were to determine the effect of phenylbutazone premedication on the pharmacokinetics and urinary excretion of frusemide in horses; and on frusemide-induced changes in urinary electrolyte excretion. Six Standardbred mares were used in a 3-way crossover design. The pharmacokinetics and renal effects of frusemide (1 mg/kg bwt i.v.) were studied with and without phenylbutazone premedication (8.8 mg/kg bwt per os 24 h before, followed by 4.4 mg/kg bwt i.v. 30 min before frusemide administration). A control (saline) treatment was also studied. Administration of frusemide without phenylbutazone led to diuresis, natriuresis, kaliuresis and chloruresis, and altered the ratio of sodium:chloride excretion from 0.4 to 1.0 in the first hour of diuresis. When frusemide and phenylbutazone were administered, sodium and chloride excretion in the first hour were significantly (P<0.05) reduced by 40 and 32%, respectively, when compared to frusemide administrationwithout phenylbutazone. The fractional clearance of sodium and chloride was also significantly reduced. Potassium excretion, potassium fractional clearance and the ratio of sodium to chloride excretion were not affected by administration of phenylbutazone. During peak diuresis, phenylbutazone did not affect the efficiency of frusemide with respect to electrolyte excretion. The plasma disposition of frusemide was not affected by phenylbutazone. However, the renal excretion of frusemide decreased by approximately 25%. We conclude that the decreased urinary excretion of frusemide by phenylbutazone led to an attenuation of frusemide-induced increases in urinary excretion of sodium and chloride. Since the efficiency of frusemide was not affected by phenylbutazone, we conclude that phenylbutazone attenuates the renal excretion of frusemide without inhibiting the intrarenal activity of frusemide in horses.

Interaction between two dicarboxylate endogenous substances, bilirubin and an uremic toxin, 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid, on human serum albumin

PURPOSE

Two dicarboxylate endogenous substances, bilirubin (BR) and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF), have a very high affinity to human serum albumin (HSA). This study was undertaken to clarify the existence of a dicarboxylate binding site on HSA.

METHODS

Chemical modification, pH dependent binding and X-ray crystallographic analysis were performed to characterize these dicarboxylate binding sites.

RESULTS

It was found the binding behavior for dicarboxylates was different from typical site I ligands such as warfarin (WF) and phenylbutazone (PB) and that electrostatic interaction was an important factor for their binding to HSA. Moreover, His residues were considered to play an important role in pH dependent binding of dicarboxylic acids but in a different manner from the site I ligands. X-ray crystallography of CMPF and BR revealed the distances between the two carboxyl groups in their chemical structures were 5.854 A and 9.979 A, respectively. This difference may be reflected in pH dependent binding. Using fluorescent probe displacement, we attempted to identify the binding site for monocarboxylate derivatives of CMPF and investigated the role of individual carboxyl group in the recognition of the binding site. The results suggested two carboxyl groups were important for the specific binding of CMPF to site I.

CONCLUSIONS

The binding site for dicarboxylic acids is located in subdomain IIA, which includes site I, on the HSA molecule. Electrostatic interaction is an important driving force for binding to HSA.

A reporter gene assay to assess the molecular mechanisms of xenobiotic-dependent induction of the human CYP3A4 gene in vitro

1. A plasmid containing 1 kb of the CYP3A4 regulatory (promoter) region coupled to a reporter gene for secretary placental alkaline phosphatase (SPAP) was transfected into HepG2 cells. Transfected cells were dosed with several known inducers of CYP3A4 and the levels of SPAP were measured. The effect of co-transfecting a plasmid encoding the human glucocorticoid receptor on reporter gene activity was also examined. 2. Dexamethasone induced CYP3A4-dependent reporter gene expression in a concentration-dependent manner and induction was approximately doubled in the presence of the glucocorticoid receptor. Dexamethasone-dependent induction was blocked by RU-486 (a glucocorticoid receptor antagonist), in the presence of the co-transfected glucocorticoid receptor. 3. Induction of CYP3A4-dependent reporter gene expression and enhancement of the induction by the glucocorticoid receptor was also observed with pregnenolone-16alpha-carbonitrile (PCN), rifampicin, phenytoin, carbamazepine, phenylbutazone and phenobarbitone, all known in vivo inducers of CYP3A4 in man. 4. Metyrapone and sulfinpyrazone induced CYP3A4-dependent reporter gene expression, but induction was not enhanced by the glucocorticoid receptor. 5. Clotrimazole, erythromycin and triacetyloleandomycin (TAO) did not induce CYP3A4-dependent reporter gene expression, consistent with the observation that these inducers act through post-transcriptional mechanisms. 6. These results highlight differences in the molecular mechanisms of induction of CYP3A4 by the xenobiotics studied and indicate that the glucocorticoid receptor is involved in the induction of the CYP3A4 gene by some, but not all, CYP3A4 inducers. 7. We propose that the approach described here provides a useful in vitro approach for the identification of transcriptional regulators of the CYP3A4 gene.

The pharmacokinetics of furosemide in anaesthetized horses after bilateral ureteral ligation

The pharmacokinetics of furosemide were investigated in anaesthetized horses with bilateral ureteral ligation (BUL) with (n = 5) or without (n = 5) premedication with phenylbutazone. Horses were administered an intravenous (i.v.) bolus dose of furosemide (1 mg/kg) approximately 60-90 min after BUL. Plasma samples collected up to 3 h after drug administration were analysed by a validated high performance liquid chromatography method. Median plasma clearance (CLp) of furosemide in anaesthetized horses with BUL was 1.4 mL/min/kg. Apparent steady state volume of distribution (Vd(ss)) ranged from 169 to 880 mL/kg and the elimination half life (t1/2) ranged from 83 min to 209 h. No differences in plasma concentration or kinetic parameter estimates were observed when phenylbutazone was administered before furosemide administration. BUL markedly reduces the elimination of furosemide in horses and models the potential effects that severe changes in kidney function may have on drug kinetics in horses.

Measurement of cyclooxygenase inhibition in vivo: a study of two non-steroidal anti-inflammatory drugs in sheep

The anti-inflammatory effects of the non-steroidal anti-inflammatory drugs phenylbutazone (PBZ) and flunixin meglumine (FM) and the relationship between the effects and drug concentration in vivo were studied using a subcutaneous tissue-cage model in sheep. Intracaveal injection of carrageenan induced prostaglandin (PG) E2 production in tissue-cage exudate (maximal concentration, 101 nM) with significant increases in white blood cell (WBC) numbers, skin temperature over the inflamed cage and exudate leukotriene B4 (LTB4) concentration (P < 0.05). Intravenous PBZ, 4.4 mg kg-1 produced mild inhibition of exudate PGE2 generation (10%), but greater inhibition of serum TXB2 (75.3%). The IC50 for TXB2 was 36.0 microM. Phenylbutazone did not alter effects on skin temperature, WBC numbers or exudate LTB4 concentrations. Intravenous FM, 1.1 mg kg-1, significantly inhibited carrageenan-induced exudate PGE2 formation (Emax, 100%, IC50, < 0.4 nM) and serum TXB2 generation (Emax, 100%, IC50, 17 nM) for up to 32 h. Flunixin meglumine significantly inhibited the rise in skin temperature but had a limited effect on exudate WBC. Phenylbutazone and FM have distinct effects on carrageenan-induced cyclooxygenase (COX-2) and platelet COX (COX-1). Flunixin meglumine was a more potent COX inhibitor than PBZ and was more selective for the inducible form of COX in vivo.

Phenylbutazone prevents the endotoxin-induced delay in gastric emptying in horses

The effect of phenylbutazone on gastric emptying in horses was determined by measuring serum concentrations of acetaminophen. Gastric emptying was determined in normal fasted horses (n = 6), horses given endotoxin intravenously (n = 6), horses given intravenous phenylbutazone (n = 6), and horses given intravenous phenylbutazone plus endotoxin (n = 6). The mean time to reach maximum serum acetaminophen concentration (Tmax), the maximum serum concentration (Cmax), and the area under the serum acetaminophen concentration versus time curve (AUC) were compared among treatment groups. Phenylbutazone did not alter gastric emptying in normal horses. Endotoxin caused a profound delay in gastric emptying, and pretreatment with phenylbutazone abolished this effect.

Synthesis of some novel pyrazole derivatives as potential antiinflammatory agents with minimum ulcerogenic activity

Two novel isomeric series, N-substituted-5-amino-4-(3,4-dimethoxyphenyl)-3-hydroxy-1 H-pyrazole-1-carboxamides (or thiocarboxamides) 6a-e, 7a, b and N-substituted-3-amino-4-(3,4-dimethoxyphenyl)-5-hydroxy-1 H-pyrazole-1-carboxamides or (thiocarboxamides) 9a-c were synthesized. Moreover, the pyrazolo-[1,5-a]-1,3,5-triazine derivative 8 was also prepared. The new compounds were tested biologically for their in vivo antiinflammatory activity (AI) against carrageenan-induced rat paw oedema. All the investigated compounds exhibited significant AI activity in the range of 23-65%. The most potent compounds were further evaluated for their ulcerogenic liability and acute toxicity. They were found to be less toxic and nearly devoid of ulcerogenic activity as compared to phenylbutazone and indometacin.

Pulmonary vascular pressures of strenuously exercising Thoroughbred horses after administration of phenylbutazone and frusemide

The present study was carried out to examine the effects of phenylbutazone treatment on the pulmonary haemodynamic effects of frusemide in strenuously exercising horses. Using catheter mounted manometers, whose in vivo signals were referenced at the point of the shoulder, heart rate, right atrial, right ventricular and pulmonary vascular pressures were measured in 3 different sets of experiments. Seven Thoroughbreds were subjected to 1) control (no medications), 2) frusemide control and 3) phenylbutazone + frusemide. The experiments were carried out in random order and were separated by 7 days. Measurements were made at rest and during incremental exercise performed on a treadmill set at 3.5% uphill grade. In the frusemide control experiment, horses received frusemide 250 mg i.v., 4 h pre-exercise. In the phenylbutazone + frusemide experiment, horses received 4 i.v. injections of phenylbutazone (4.4 mg/kg bwt) at 12 h intervals. Twenty-four hours after the last phenylbutazone injection, horses received frusemide 250 mg i.v. and exercise was performed 4 h later. This latter regimen mimics prevailing veterinary practice at Illinois racetracks. The highest work intensity (14.2 m/s, 3.5% uphill grade) elicited maximal heart rate of horses. Significant right atrial, as well as pulmonary arterial, capillary and venous hypertension occurred with exertion in all 3 experiments. However, in the frusemide-control and the phenylbutazone + frusemide studies, the exercise induced rise in mean right atrial and pulmonary vascular pressures was significantly (P<0.05) attenuated in comparison with that in the control experiments. Statistically significant differences were not found between the frusemide control study and the phenylbutazone + frusemide study either at rest or during any level of exertion. Therefore, it was concluded that the phenylbutazone treatment in our study did not mitigate the pulmonary haemodynamic effects of frusemide in strenuously exercising Thoroughbred horses.

The effect of streptomycin, oxytetracycline, tilmicosin and phenylbutazone on spermatogenesis in bulls

To determine whether declining semen quality associated with health problems may be due to certain antibiotic or anti-inflammatory treatments, semen was collected 3 times per week for up to 42 d from 6 normal bulls after treatment with oxytetracycline, tilmicosin, dihydrostreptomycin, or phenylbutazone. No adverse effects on semen quality were observed.