Phenylbutazone Research Articles

Synthesis and anti-inflammatory activity of 2-aryloxy methyl oxazolines

A series of potential biologically active 2-aryloxy methyl oxazolines 3a– n have been synthesized from substituted hydroxybenzenes 1a– n with good chemical yield. The compounds 3a– n were screened for their anti-inflammatory, ulcerogenic, cyclooxygenase activities and also for their acute toxicity. The potency of the compounds was compared with that of the standard drugs, aspirin and phenyl butazone. The outcome indicates that compounds 3b (48.2%), 3h (48.5%) and 3l (46.5%) offered significant anti-inflammatory activity with low ulcerogenic activity than the standard drugs.

Amino acid positions 69–132 of UGT1A9 are involved in the C-glucuronidation of phenylbutazone

Phenylbutazone (PB) is known to be biotransformed to its O- and C-glucuronide. Recently, we reported that PB C-glucuronide formation is catalyzed by UGT1A9. Interestingly, despite UGT1A8 sharing high amino acid sequence identity with UGT1A9, UGT1A8 had no PB C-glucuronidating activity. In the present study, we constructed eight UGT1A9/UGT1A8 chimeras and evaluated which region is important for PB C-glucuronide formation. All of the chimeras and UGT1A8 and UGT1A9 had 7-hydroxy-(4-trifluoromethyl)coumarin (HFC) O-glucuronidating activity. The K m values for HFC glucuronidation of UGT1A8, UGT1A9 and their chimeras were divided into two types, UGT1A8 type (high K m) and UGT1A9 type (low K m), and these types were determined according to whether their amino acids at positions 69–132 were those of UGT1A8 or UGT1A9. Likewise, PB O-glucuronidating activity was also detected by all of the chimeras, and their K m values were divided into two types. On the contrary, PB C-glucuronidating activity was detected by UGT1A9 (1–132)/1A8 (133–286), UGT1A9 (1–212)/1A8 (213–286), UGT1A8 (1–68)/1A9 (69–286), and UGT1A8 (1–68)/1A9 (69–132)/1A8 (133–286) chimeras. The region 1A9 (69–132) was common among chimeras having PB C-glucuronidating activity. Of interest is that UGT1A9 (1–68)/1A8 (69–132)/1A9 (133–286) had lost PB C-glucuronidation activity, but retained activities of PB and HFC O-glucuronidation. These results strongly suggested that amino acid positions 69–132 of UGT1A9 are responsible for chemoselectivity for PB and affinity to substrates such as PB and HFC.

Thiazolyl/oxazolyl formazanyl indoles as potent anti-inflammatory agents

A series of 3-(2′-substituted indolidene aminothiazol-4′-yl)-2-(4-chlorophenyl) indoles ( 3a– 3d), 3-(2′-substituted indolidene amino oxazol-4′-yl)-2-(4-chlorophenyl) indoles ( 3a′– 3d′) and 3-[2′-(1′-substituted phenyl-3′-substituted indolyl formazan-4′-yl) thiazol-4′-yl]-2-(4-chlorophenyl) indoles ( 4a– 4h), 3-[2′-(1′-substituted phenyl-3′-substituted indolyl formazan-4′-yl) oxazol-4′-yl]-2-(4-chlorophenyl) indoles ( 4a′– 4h′) were synthesized and evaluated for their anti-inflammatory activity against carrageenan induced oedema in albino rats at a dose of 50 mg/kg p.o. The structure of all these compounds were established on the basis of elemental and spectral (IR, 1H NMR and mass spectral data) studies. All the compounds of this series show moderate to good activity. The most active compound of this series 3-(2′-methyl indolidene aminothiazol-4′-yl)-2-(4-chlorophenyl) indole ( 3b) is found to be the most potent and has shown higher percent of inhibition of oedema, lower ulcerogenic liability and acute toxicity than the reference drug phenyl butazone.

Effects of single‐dose intravenous phenylbutazone on experimentally induced, reversible lameness in the horse

The objective was to test the hypothesis that phenylbutazone (PBZ) alleviates lameness in an adjustable heart bar shoe model of equine foot pain. Eight Quarter Horse mares underwent 4-weekly treatments randomly: 0.9% saline placebo (SAL: 1 mL/45 kg body weight i.v.) with no lameness; SAL with lameness; PBZ (4.4 mg/kg body weight i.v.) with no lameness; and PBZ with lameness. Blinded heart rate (HR) and lameness score (LS) were assessed every 20 min for 2 h and then hourly through 9 h. At 1 h SAL or PBZ was administered. Jugular venous samples were obtained at hours 0, 1, 2, 4, 6, and 8 and were evaluated for packed cell volume (PCV), cortisol, and drug concentrations. Repeated measures anova and t-tests were used to identify PBZ effects at a significance level of P<0.05. PBZ-treated LS was lower 2-8 h post-treatment, and HR was lower from 2 through 6 h post-treatment (P<0.05). Phenylbutazone did not change PCV and had minimal effect on cortisol. Mean plasma PBZ and oxyphenbutazone concentrations 7 h after treatment were 7.2-7.5 and 1.6-1.9 microg/mL, respectively. It was concluded that PBZ was efficacious in alleviating lameness in this model. Cortisol and PCV were not discriminating enough to distinguish between PBZ-treated and SAL-treated trials.

ANTIINFLAMATORY ACTIVITY OF PEUCEDANUM OFFICINALE ON RATS

Peucedanum officinale , ( fam. Apiaceae ), belongs to a large group of medicinal plants, sp read around the world, used for wide range therapeutic p urposes. Antiinflammatory action has been tested on kaolin rat paw oedema model (measured by plethysmography), efficiency of Peucedanum officinale , has been compared to those of phenylbutazone. Inflammatory oedema represent the difference between the injected paw volume at 2, 4, respectively 24 hours and initial v olume; the inhibition of oedema represents the diff erence in paw volume, between treated animals ( Peucedanum officinale and phenylbutazone) and untreated ones. Acute toxicity test has revealed no pathological changes in animals in study. Antiinflammatory effect reflec ted by inhibition of oedema has the highest value on 4h de termination, but the difference to negative control group was statistically significant in all the determinations . However, the antiinflammatory efficiency has been lower as compared to phenylbutazone. Peucedanum officinale has proved a significant antiinflammatory activity ; therefore, it might be useful for patients unsuitab le for classical antiinflammatory therapy.

Identification of human UDP-glucuronosyltransferase isoform(s) responsible for the C-glucuronidation of phenylbutazone

Glucuronidation is a major metabolic pathway in the biotransformation of many xenobiotics and endogeneous compounds. There have been many studies on the formation of O-, N- or S-glucuronides and identification of the UDP-glucuronosyltransferase (UGT) isoforms responsible for the formation of these glucuronides. However, there is no information available on which UGT isoform(s) catalyzes C-glucuronidation. In the present study, 16 human UGTs (UGTs 1A1, 1A3, 1A4, 1A5, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28) were cloned and expressed in baculovirus-infected insect cells and investigated to determine their C-glucuronidating activity toward phenylbutazone (PB). Among the UGT isoforms investigated, only UGT1A9 catalyzed PB C-glucuronidation. Human liver and kidney microsomes, which are well known to express UGT1A9, had C-glucuronidating activity toward PB. However, the jejunum, which did not express UGT1A9, had no C-glucuronidating activity. These results demonstrate for the first time that PB C-glucuronidation is catalyzed by only UGT1A9.

Simultaneous and minimally invasive assessment of muscle tolerance and bioavailability of different volumes of an intramuscular formulation in the same animals1

Evaluation of skeletal muscle tolerance during development of new drug formulations for i.m. use is most often based on terminal methods performed in the target species after slaughtering. The objective of this study was to evaluate the effect of muscle damage on the pharmacokinetic parameters of the drug delivered into the muscle using an alternative, noninvasive method. Phenylbutazone (PBZ) was used as the test article. Six ewes received increasing volumes of a 20% PBZ i.m. formulation, according to a cross-over design, and an i.v. bolus of the same formulation. Serial blood samples were taken, and a pharmacokinetic analysis of the plasma activity of creatine kinase and plasma PBZ concentrations was carried out. The amount of muscle damage after i.m. administration of 2, 4, or 8 mL of PBZ, calculated from the area under the curve of plasma creatine kinase across time was 36, 76, and 178 g for a 70-kg ewe. The corresponding absolute bioavailability of PBZ was 100 +/- 32%, 96 +/- 19%, and 100 +/- 17%, and the maximal PBZ concentrations were 42 +/- 3.4, 74 +/- 8.8, and 119 +/- 18.2 microg/mL. The plasma clearance of PBZ (i.v.) was 4.2 +/- 0.94 mL.kg(-1).h(-1). In conclusion, the absolute bioavailability of PBZ after i.m. administration was not altered by the increased volume of formulation administered despite the overall increase in the extent of muscle damage.

Crotasteroiridocin: A New Steroiridoid from Crotalaria emarginella and its anti-Inflammatory Activity

The aerial parts of Crotalaria emarginella Vatke (Leguminosae) have afforded a new steroidiridoid, characterized as 1’-hydroxy-isoiridomyrmecinyl- 1’-O-β -3-O-α-stigmast-5-ene, designated as crotasteroiridocin (1), which shows a unique combination of iridoid and sterol units, found very rarely in nature. Furthermore, a rare iridoid glucoside namely, bis-desoxy-dihydro-monotropein (2) has also been isolated from the aerial parts of the plant. The structures of the isolated products were elucidated on the basis of spectral and chemical studies. The anti-inflammatory activity has also been screened, wherein compounds 1 and 2 have shown 25.92% and 28.39% activity respectively, with respect to phenyl butazone against carrageenan employing the rat paw method.

Effects of phenylbutazone alone or in combination with flunixin meglumine on blood protein concentrations in horses

To assess effects of treatment with phenylbutazone (PBZ) or a combination of PBZ and flunixin meglumine in horses. 24 adult horses. 13 horses received nonsteroidal antiinflammatory drugs (NSAIDs) in a crossover design. Eleven control horses were exposed to similar environmental conditions. Treated horses received PBZ (2.2 mg/kg, PO, q 12 h, for 5 days) and a combination of PBZ and flunixin meglumine (PBZ, 2.2 mg/kg, PO, q 12 h, for 5 days; flunixin meglumine, 1.1 mg/kg, IV, q 12 h, for 5 days). Serum samples were obtained on day 0 (first day of treatment) and day 5, and total protein, albumin, and globulin were measured. 1 horse was euthanatized with severe hypoproteinemia, hypoalbuminemia, and colitis during the combination treatment. Comparisons revealed no significant difference between control horses and horses treated with PBZ alone. There was a significant difference between control and treated horses when administered a combination of PBZ and flunixin meglumine. Correction for horses with values >2 SDs from the mean revealed a significant difference between control horses and horses administered the combination treatment, between control horses and horses administered PBZ alone, and between horses receiving the combination treatment and PBZ alone. Gastroscopy of 4 horses revealed substantial gastric ulcers when receiving the combination NSAID treatment. Analysis of results of the study indicates the need for caution when administering a combination NSAID treatment to horses because the detrimental effects may outweigh any potential benefits.

Effect of aqueous extract ofTragia involucrata Linn. on acute and subacute inflammation

Antiinflammatory activity of aqueous extract of Tragia involucrata was tested on carrageenan-induced hind paw oedema and cotton pellet granuloma models in albino rats. In the subacute model, cotton pellet granuloma was produced by implantation of 10 mg sterile cotton in the axilla under ether anaesthesia. The animals were administered an aqueous extract at various concentrations of 50, 100, 200, 300 and 400 mg/kg. Phenyl butazone (80 mg/kg) was used as a standard drug. The paw diameter was measured at different time intervals and the dry granuloma weight was taken after the treatment. The aqueous leaf extract (400 mg/kg) showed the maximum inhibition (84.23%) of oedema at the end of 3 h following carrageenin-induced rat paw oedema. In subacute inflammation, the extract showed 76.25% reduction in granuloma weight. The results prove that the aqueous leaf extract showed highest antiinflammatory activity in acute and subacute inflammation and also support the usage of traditional claims.

Antiinflammatory Efficacy of Extracts of Latex of Calotropis procera Against Different Mediators of Inflammation

The latex of the plant Calotropis procera has been reported to exhibit potent antiinflammatory activity against carrageenin and formalin that are known to release various mediators. In the present study, we have evaluated the efficacy of extracts prepared from the latex of C procera against inflammation induced by histamine, serotonin, compound 48/80, bradykinin (BK), and prostaglandin E2(PGE2) in the rat paw oedema model. The paw oedema was induced by the subplantar injection of various inflammagens and oedema volume was recorded using a plethysmometer. The aqueous and methanol extracts of the dried latex (DL) and standard antiinflammatory drugs were administered orally 1 hour before inducing inflammation. The inhibitory effect of the extracts was also evaluated against cellular influx induced by carrageenin. The antiinflammatory effect of aqueous and methanolic extracts of DL was more pronounced than phenylbutazone (PBZ) against carrageenin while it was comparable to chlorpheniramine and PBZ against histamine and PGE2, respectively. Both extracts produced about 80%, 40%, and 30% inhibition of inflammation induced by BK, compound 48/80, and serotonin. The histological analysis revealed that the extracts were more potent than PBZ in inhibiting cellular infiltration and subcutaneous oedema induced by carrageenin. The extracts of DL exert their antiinflammatory effects mainly by inhibiting histamine and BK and partly by inhibiting PGE2.

Interleukin-1β inhibits paw oedema induced by local administration of latex of Calotropis procera extracts

Interleukin-1beta (IL-1beta), a pro-inflammatory cytokine, has been reported to exhibit anti-inflammatory properties in the carrageenan-induced paw oedema model. In the present study, we have evaluated the anti-inflammatory activity of IL-1beta against inflammation induced by local administration of the methanol extract of dried latex of Calotropis procera (MeDL) and compared it with that against carrageenan. The anti-inflammatory activity of standard anti-inflammatory drugs, phenylbutazone (PBZ) and dexamethasone (DEX), was also evaluated against both inflammagens. Injection of an aqueous solution of dried latex and MeDL into the sub-plantar surface of the rat paw produced intense inflammation with a peak response occurring within 2 h, while the peak inflammatory response with carrageenan was obtained at 3 h. Subcutaneous injection of IL-1beta was found to be more effective against the inflammatory response elicited by carrageenan (70% inhibition) as compared to MeDL (50% inhibition) at 20microg/kg dose. On the other hand, PBZ effectively inhibited the inflammatory response elicited by both MeDL and carrageenan, while DEX was more effective against carrageenan. Thus, our study indicates that the difference in the anti-inflammatory effect of IL-1beta against latex of C. procera extract and carrageenan is due to the release of different mediators released by these inflammagens.

Antinociceptive and anti-inflammatory effects of Dorstenia barteri (Moraceae) leaf and twig extracts in mice

The present study was undertaken to investigate the antinociceptive and anti-inflammatory activities of the leaf and twig extracts of Dorstenia barteri (Moraceae) in mice. Both the leaf and twig extracts of Dorstenia barteri at 50, 100 and 200 mg/kg showed significant ( P < 0.05–0.01) antinociceptive activities in chemical-, mechanical- and thermal-induced pain test models. Intraperitoneal administration of the plant extracts at 50, 100 and 200 mg/kg significantly ( P < 0.05–0.01) inhibited carrageenin-induced acute inflammation in oedema paw weight, pulmonary oedema and number of pleural leucocytes in a dose-dependent way. The twig extract was found to be more active than the leaf extract in all the experimental models used. The inhibitory effects of the plant extracts were comparable to those of the reference drugs acetylsalicyclic acid (ASA) and phenylbutazone (PBZ) at 100 mg/kg i.p. The significant reduction in acetic acid-induced abdominal contractions, the decrease in oedema paw weight as well as in the number of leucocytes in the pleural cavity exudates, and the significant increase in the reaction time and pain threshold of mice observed in this study suggest that Dorstenia barteri extracts possess both anti-inflammatory and antinociceptive activities. The present study, therefore, lend pharmacological support to the folkloric uses of Dorstenia barteri extracts in the treatment, control and/or management of arthritis, rheumatism, gout, headache and other forms of body pains in some parts of Africa.

Effect of anti-inflammatory drugs on pleurisy induced by latex of Calotropis procera in rats

In present study, we have characterized the inflammation induced by latex of Calotropis procera in the rat pleurisy model and evaluated the effect of various inhibitors of inflammatory mediators. Injection of dried latex (DL) into the pleural cavity elicited an acute inflammatory response characterized by protein rich fluid accumulation and leucocyte (polymorphonuclear cells, and mononuclear cells) infiltration in the pleural cavity. The peak inflammatory response was obtained at 6 h when the fluid volume, protein concentration and cell infiltration were maximum. All these parameters were attenuated by phenylbutazone (PBZ), celecoxib, dexamethasone, cyproheptadine and chlorpheniramine. All these drugs were also effective in inhibiting the production of prostaglandin E 2 (PGE 2). Of all the drugs tested, dexamethasone was most effective in inhibiting DL induced pleurisy. The results clearly indicate that prostaglandins (PGs) and biogenic amines play a key role in the development of pleurisy induced by DL and it serves as a model to evaluate drugs inhibiting cellular influx associated with inflammatory response.

Development and Validation of a Method for the Determination of Phenylbutazone Drug Residues in Bovine, Equine, and Porcine Muscle Tissues Using HPLC with UV Detection

A sensitive liquid chromatographic method with UV detection has been developed for the analysis of phenylbutazone (PBZ) drug residues in bovine, equine, and porcine muscle tissues. PBZ is extracted from muscle tissues with ethyl acetate/methanol solution containing DL‐dithiothreitol. The tissue extract is centrifuged, evaporated to minimum volume under nitrogen, and cleaned up on a conditioned Florisil solid phase extraction cartridge. PBZ is eluted with a 1:1 mixture of ether and a solution of methylene chloride:methanol:acetic acid (94:4:2 v/v/v). The eluate is evaporated to dryness with nitrogen, reconstituted in mobile phase, filtered, and analyzed by reversed‐phase liquid chromatography with UV detection at 270 nm. The method, with a detection limit of 3 ppb, was used to monitor the prevalence of PBZ drug residues in equine, porcine, and bovine muscle tissues obtained from animals slaughtered in federally inspected Canadian abattoirs.

Lower gastric ulcerogenic effect of suxibuzone compared to phenylbutazone when administered orally to horses

The objective was to compare the gastrointestinal and general toxicity of suxibuzone (SBZ) to that of phenylbutazone (PBZ) when administered orally in horses. Fifteen healthy horses were allocated to three treatment groups. One group received a high dose of PBZ for two weeks; the second group was given an equimolecular dosage of SBZ; and a third group received placebo. Horses were daily monitored, and blood samples were collected before and during the study. On day 18, complete post-mortem examinations were performed. One horse treated with PBZ showed clinical signs of NSAID toxicosis. Small oral ulcers were also detected in other two horses from the PBZ group and in two horses from the SBZ group. There were no statistical differences in the blood parameters among groups. Ulcers in the stomach’s glandular mucosa were observed in all horses of the PBZ group, while only two horses of the SBZ group showed ulcerations. PBZ horses had a significant higher ulcerated area, and gastric ulcers were significantly deeper than those in the SBZ and placebo groups. No other lesions were found in any other tissue. In conclusion, SBZ causes significantly lower gastric ulcerogenic effect than PBZ when administered orally at equimolecular doses in horses.

Effects of lipopolysaccharide and phenylbutazone on gastric contents in the horse

Endotoxaemia causes a disruption of gastrointestinal motility in the horse but there is no information on its effects on gastric secretion. Lipopolysaccharide (LPS) administration is known to affect gastric secretion in other species. That LPS, a toxic component of Gram-negative bacteria, would reduce gastric acid secretion and that pretreatment with phenylbutazone (PBZ) would block the effects of LPS. The effects of LPS and PBZ on gastric contents were investigated in fasted, mature horses, with permanent gastric cannulae. Horses were pretreated with either saline or PBZ 15 mins before a 60 min infusion of either LPS or saline. Gastric contents were collected at 15 min intervals for 3 h, beginning 15 mins after the start of the LPS or saline infusion. Lipopolysaccharide significantly decreased gastric acid output, [K+] and potassium output and increased [Na+] and sodium output. Phenylbutazone did not affect basal gastric acid secretion but decreased LPS-induced changes in the secreted volume, [Na+] and sodium output. This study provides evidence that LPS affects gastric acid secretion in the horse and that these LPS-induced changes are mediated, in part, by prostaglandins. Lipopolysaccharide administration can induce changes in the composition of gastric contents in the horse but further work is needed to determine the source of these changes.

Confirmation of Phenylbutazone Residues in Bovine Kidney by Liquid Chromatography/Mass Spectrometry

A confirmatory method is described for phenylbutazone (PB) residues in bovine kidney tissue. Ground kidney tissue is diluted with water, and the mixture is made basic with 25% ammonium hydroxide in water; the lipids are extracted with ethyl and petroleum ethers. The ether layer is discarded, and the tissue is acidified with 6N HCl. PB residues are extracted with tetrahydrofuranhexane (1 + 4). The extract is passed through a silica solid-phase extraction column, and the eluate is evaporated to dryness. The residue is dissolved in acidified acetonitrile-water-acetic acid (50 + 49.4 + 0.6). A single quadrupole mass spectrometer coupled to a liquid chromatograph with an electrospray interface is used to confirm the identity of the PB residues in the kidney extract. Negative-ion detection with selected-ion monitoring of 4 ions is used. Sets of control and fortified-control kidney tissues (at 50, 100, and 200 ppb PB) and several kidney tissue field samples were analyzed for method validation. The method was tested further during the course of a survey to determine the incidence of PB residues in bovine kidney samples obtained from slaughterhouses across the country. In addition, the method was tested for use with an ion-trap mass spectrometer coupled to a liquid chromatograph, which allowed confirmation of PB at lower levels (5-10 ppb) in kidney tissue.

Pharmacodynamics and pharmacokinetics of phenylbutazone in calves.

Phenylbutazone (PBZ) was administered to six calves intravenously (i.v.) and orally at a dose rate of 4.4 mg/kg in a three-period cross-over study incorporating a placebo treatment to establish its pharmacokinetic and pharmacodynamic properties. Extravascular distribution was determined by measuring penetration into tissue chamber fluid in the absence of stimulation (transudate) and after stimulation of chamber tissue with the mild irritant carrageenan (exudate). PBZ pharmacokinetics after i.v. dosage was characterized by slow clearance (1.29 mL/kg/h), long-terminal half-life (53.4 h), low distribution volume (0.09 L/kg) and low concentrations in plasma of the metabolite oxyphenbutazone (OPBZ), confirming previously published data for adult cattle. After oral dosage bioavailability (F) was 66%. Passage into exudate was slow and limited, and penetration into transudate was even slower and more limited; area under curve values for plasma, exudate and transudate after i.v. dosage were 3604, 1117 and 766 microg h/mL and corresponding values after oral dosage were 2435, 647 and 486 microg h/mL. These concentrations were approximately 15-20 (plasma) and nine (exudate) times greater than those previously reported in horses (receiving the same dose rate of PBZ). In the horse, the lower concentrations had produced marked inhibition of eicosanoid synthesis and suppressed the inflammatory response. The higher concentrations in calves were insufficient to inhibit significantly exudate prostaglandin E2 (PGE2), leukotriene B4 (LTB4) and beta-glucuronidase concentrations and exudate leucocyte numbers, serum thromboxane B2 (TxB2), and bradykinin-induced skin swelling. These differences from the horse might be the result of: (a) the presence in equine biological fluids of higher concentrations than in calves of the active PBZ metabolite, OPBZ; (b) a greater degree of binding of PBZ to plasma protein in calves; (c) species differences in the sensitivity to PBZ of the cyclo-oxygenase (COX) isoenzymes, COX-1 and COX-2 or; (d) a combination of these factors. To achieve clinical efficacy with single doses of PBZ in calves, higher dosages than 4.4 mg/kg will be probably required.

Effects of anti-arthritis preparations on gene expression and enzyme activity of cyclooxygenase-2 in cultured equine chondrocytes.

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. Articular cartilage from 9 young adult horses. 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), polysulfated glycosaminoglycan, and hyaluronan, each at concentrations of 10 and 100 microg/ml and each with or without reIL-1beta. A commercial immunoassay was used to determine prostaglandin E2 (PGE2) concentrations in conditioned medium of similarly treated cells to quantify COX-2 activity. Addition of reIL-1beta increased the expression of COX-2 in a dose-dependent manner, which was paralleled by an increased concentration of PGE2 in culture medium. Concentration of PGE2 in spent medium from reIL-beta-treated chondrocytes was significantly reduced by DEX and PBZ; however, only DEX significantly reduced gene expression of COX-2. Prostaglandin E2 is considered to be an important mediator in the pathophysiologic processes of arthritis, and cultured chondrocytes respond to interleukin-1 with enhanced expression and activity of COX-2. Palliative relief in affected horses is probably attributable, in part, to inhibition of PGE2 synthesis; however, analysis of these data suggests that of the 4 compounds tested, only DEX affects pretranslational regulation of the COX-2 gene in cultured equine chondrocytes.