Influence of age, site, and degenerative state on the speed of sound in equine articular cartilage

OBJECTIVE: To determine the speed of sound (SOS) in equine articular cartilage and investigate the influence of age, site in the joint, and cartilage degeneration on the SOS. SAMPLE POPULATION: Cartilage samples from 38 metacarpophalangeal joints of 38 horses (age range, 5 months to 22 years). PROCEDURE: Osteochondral plugs were collected from 2 articular sites of the proximal phalanx after the degenerative state was characterized by use of the cartilage degeneration index (CDI) technique. The SOS was calculated (ratio of needle-probe cartilage thickness to time of flight of the ultrasound pulse), and relationships between SOS value and age, site, and cartilage degeneration were evaluated. An analytical model of cartilage indentation was used to evaluate the effect of variation in true SOS on the determination of cartilage thickness and dynamic modulus with the ultrasound indentation technique. RESULTS: The mean SOS for all samples was 1,696 +/- 126 m/s. Age, site, and cartilage degeneration had no significant influence on the SOS in cartilage. The analytical model revealed that use of the mean SOS of 1,696 m/s was associated with maximum errors of 17.5% on cartilage thickness and 70% on dynamic modulus in an SOS range that covered 95% of the individual measurements. CONCLUSIONS AND CLINICAL RELEVANCE: In equine articular cartilage, use of mean SOS of 1,696 m/s in ultrasound indentation measurements introduces some inaccuracy on cartilage thickness determinations, but the dynamic modulus of cartilage can be estimated with acceptable accuracy in horses regardless of age, site in the joint, or stage of cartilage degeneration.     

Functional adaptation of equine articular cartilage: the formation of regional biochemical characteristics up to age one year

Biochemical heterogeneity of cartilage within a joint is well known in mature individuals. It has recently been reported that heterogeneity for proteoglycan content and chondrocyte metabolism in sheep develops postnatally under the influence of loading. No data exist on the collagen network in general or on the specific situation in the horse. The objective of this study was to investigate the alterations in equine articular cartilage biochemistry that occur from birth up to age one year, testing the hypothesis that the molecular composition of equine cartilage matrix is uniform at birth and biochemical heterogeneity is formed postnatally. Water content, DNA content, glycosaminoglycan content (GAG) and biochemical characteristics of the collagen network (collagen content, hydroxylysine content and hydroxylysylpyridinoline [HP] crosslinks) were measured in immature articular cartilage of neonatal (n = 16), 5-month-old foals (n = 16) and yearlings (n = 16) at 2 predefined differently loaded sites within the metacarpophalangeal joint. Statistical differences between sites were analysed by ANOVA (P<0.01), and age correlation was tested by Pearson's product moment correlation analysis (P<0.01). In neonatal cartilage no significant site differences were found for any of the measured biochemical parameters. This revealed that the horse has a biochemically uniform joint (i.e. the cartilage) at birth. In the 5-month-old foals and yearlings, significant site differences, comparable to those in the mature horse, were found for DNA, GAG, collagen content and hydroxylysine content. This indicates that functional adaptation of articular cartilage to weight bearing for these biochemical parameters takes place during the first months postpartum. Water content and HP crosslinks showed no difference between the 2 sites from neonatal horses, 5-month-old animals and yearlings. At both sites water, DNA and GAG decreased during maturation while collagen content, hydroxylysine content and HP crosslinks increased. We propose that a foal is born with a uniform biochemical composition of cartilage in which the functional adaptation to weight bearing takes place early in life. This adaptation results in biochemical and therefore biomechanical heterogeneity and is thought to be essential to resist the different loading conditions to which articular cartilage is subjected during later life. As collagen turnover is extremely low at mature age, an undisturbed functional adaptation of the collagen network of articular cartilage at a young age may be of significant importance for future strength and resistance to injury.     

The influence of strenuous exercise on collagen characteristics of articular cartilage in Thoroughbreds age 2 years

In order to assess the influence of strenuous exercise on collagen characteristics of articular cartilage, the response of the collagen network was studied in seven 2-year-old Thoroughbreds subjected to strenuous exercise compared to 7 nontrained individuals. After 13 weeks, the animals were subjected to euthanasia, fetlock joints of the forelimbs were scored macroscopically after Indian Ink staining, and articular cartilage from different locations of the articular surface of the proximal first phalanx was sampled and analysed for water content, collagen content, hydroxylysine content and amount of hydroxylysylpyridinoline (HP) crosslinks. Gross lesions were significantly more severe in the exercised than in the nonexercised group. In the control animals, the characteristic site-specific differences in collagen parameters were found as described earlier, but in the strenuously exercised animals this physiological biochemical heterogeneity had disappeared. In the exercised animals, an increase in water content and a sharp decrease in HP crosslinking was found that was correlated with the presence of wear lines. It is concluded that the strenuous exercise provoked significant alterations in the characteristics of the collagen network of the articular cartilage of the fetlock joint which were suggestive of microdamage and loosening of the collagen network. The collagen component of cartilage, in contrast to the proteoglycan component, is known to have a very limited capacity for repair and remodelling due to an extremely low turnover rate. Therefore, alterations within the articular collagen network might be expected to play an important role in the pathophysiology of degenerative joint disorders.     

Influence of polysulfated glycosaminoglycan on equine articular cartilage in explant culture.

Articular cartilage explants from 3 horses were maintained in tissue culture to test the effects of a polysulfated glycosaminoglycan on proteoglycan biosynthesis. Cultures were exposed to concentrations of 0, 50, or 200 micrograms of the drug/ml for either 2 days or 6 days, and labeled with 35S, before measuring the content of sulfated proteoglycan in the culture media and in extracts of cartilage. In a second experiment, the explants were incubated with the isotope and subsequently exposed to the same concentrations of the polysulfated glycosaminoglycan for 4 days. Subsequently, the amount of remaining labeled proteoglycan was determined. Gel filtration chromatography was used to compare the hydrodynamic size of proteoglycans from the cartilage explants in each experiment. Polysulfated glycosaminoglycan caused a dose-dependent depression of sulfated proteoglycan synthesis, which was statistically significant after 6 days of exposure. Radioactive proteoglycan content in explants was similar in the experiment involving isotopic labeling prior to exposure to the drug. Proteoglycan monomer size was similar in all treatment groups. It was concluded that polysulfated glycosaminoglycan caused a modest depression in proteoglycan synthesis, had little effect on endogenous proteoglycan degradation, and did not influence the size of sulfated proteoglycans synthesized by normal equine chondrocytes in explant culture.     

Development of biochemical heterogeneity of articular cartilage: influences of age and exercise

The objective of this study was to document the development of biochemical heterogeneity from birth to maturity in equine articular cartilage, and to test the hypothesis that the amount of exercise during early life may influence this process. Neonatal foals showed no biochemical heterogeneity whatsoever, in contrast to a clear biochemical heterogeneity in mature horses. The process of formation of site differences was almost completed in exercised foals age 5 months, but was delayed in those deprived of exercise. For some collagen-related parameters, this delay was not compensated for after an additional 6 month period of moderate exercise. It is concluded that the functional adaptation of articular cartilage, as reflected in the formation of biochemical heterogeneity in the horse, occurs for the most part during the first 5 months postpartum. A certain level of exercise seems essential for this process and withholding exercise in early life, may result in a delay in the adaptation of the cartilage.     

Influence of exercise and joint topography on depth‐related spatial distribution of proteoglycan and collagen content in immature equine articular cartilage

Reasons for performing study: There is ample evidence on topographical heterogeneity of the principal biochemical components of articular cartilage over the surface of the joint and the influence of loading thereon, but no information on depth‐related zonal variation in horses. Objectives: To study depth‐related zonal variation in proteoglycan (PG) and collagen content in equine articular cartilage. Methods: Two techniques (safranin‐O densitometry and Fourier transform infrared spectroscopy) were applied to sections of articular cartilage from the proximal phalangeal bone of the metacarpophalangeal joint of 18‐month‐old Thoroughbreds that had been raised at pasture from age 0–18 months without (PASTEX) and with (CONDEX) additional exercise. Two sites were investigated: site 1 at the joint margin that is unloaded at rest or at slow gaits, but subjected to high‐intensity loading during athletic activity; and site 2, a continuously, but less intensively, loaded site in the centre of the joint. Results: Proteoglycan values increased from the surface to the deep layers of the cartilage, collagen content showed a reverse pattern. PG content was significantly higher at site 2 in both PASTEX and CONDEX animals without an effect of exercise. In the PASTEX animals collagen content was significantly higher at site 1, but in the CONDEX group the situation was reversed, due to a significant exercise effect on site 1, leading to a reduced collagen content. Conclusions: Collagen and PG content gradients agree with findings in other species. The observations on PG levels suggest that the exercise level was not strenuous. The collagen results in the PASTEX group confirmed earlier findings, the lower levels at site 1 in the CONDEX group being possibly due to an advancement of the physiological maturation process of collagen remodelling. Potential relevance: This study confirms earlier observations that even moderate variations in exercise level in early age may have significant effects on the collagen network of articular cartilage.     

The effect of sodium heparin on equine articular cartilage.

This study compared the effect of sodium heparin and gentamicin sulphate on equine articular cartilage (AC) explants in order to investigate the possible use of sodium heparin in the treatment of infectious arthritis. Six concentrations of sodium heparin and gentamicin sulphate were tested. The supernatant and explant digest were assayed for glycosaminoglycan (GAG) content with the dimethyl-methylene blue assay and the per cent loss of GAG was calculated. A significant (P< 0.001) increase in percentage GAG loss was noted for the sodium heparin groups when compared to the control, whilst no significant increase was found among the treatment groups (P =0.782). For gentamicin, no significant difference in percentage GAG loss was found between the control and three of the five treatment groups (P =0.667). The percentage GAG loss in the sodium heparin treated AC explants was greater than for any of the gentamicin-treated AC explants. It can be concluded that sodium heparin sulphate stimulates an increase in GAG release from equine articular cartilage explants, though no firm conclusions can be drawn on its use in treating equine infectious arthritis. Copyright Harcourt Publishers Ltd.     

Use of an antineoepitope antibody for identification of type-II collagen degradation in equine articular cartilage.

OBJECTIVE: To develop an antibody that specifically recognizes collagenase-cleaved type-II collagen in equine articular cartilage. SAMPLE POPULATION: Cartilage specimens from horses euthanatized for problems unrelated to the musculoskeletal system. PROCEDURE: A peptide was synthesized representing the carboxy- (C-) terminus (neoepitope) of the equine type-II collagen fragment created by mammalian collagenases. This peptide was used to produce a polyclonal antibody, characterized by western analysis for reactivity to native and collagenase-cleaved equine collagens. The antibody was evaluated as an antineoepitope antibody by ELISA, using peptides +/- an amino acid at the C-terminus of the immunizing peptide. Collagen cleavage was assayed from equine articular cartilage cultured with interleukin-1 (IL-1), +/- a synthetic MMP inhibitor, BAY 12-9566. Cartilage specimens from osteoarthritic and nonarthritic joints were compared for antibody staining. RESULTS: An antibody, 234CEQ, recognized only collagenase-generated 3/4-length fragments of equine type-II collagen. This was a true antineoepitope antibody, as altering the C-terminus of the immunizing peptide significantly decreased competition for binding in an inhibition ELISA. The IL-1-induced release of type-II collagen fragments from articular cartilage was prevented with the MMP inhibitor. Cartilage from an osteoarthritic joint of a horse had increased staining with the 234CEQ antibody, compared with normal articular cartilage. CONCLUSIONS AND CLINICAL RELEVANCE: We generated an antineoepitope antibody recognizing collagenase-cleaved type-II collagen of horses. This antibody detects increases in type-II collagen cleavage in diseased equine articular cartilage. The 234CEQ antibody has the potential to aid in the early diagnosis of arthritis and to monitor treatment responses.     

Effects of polysulfated glycosaminoglycan on chemical and physical defects in equine articular cartilage

The effect of intra-articular polysulfated glycosaminoglycan (PSG) on repair of chemical and physical articular cartilage injuries was evaluated in 8 horses. In each horse, a partial- and a full-thickness articular cartilage defect was made on the distal articular surface of the radial carpal bone. In the contralateral middle carpal joint, a chemical articular cartilage injury was induced by injecting 50 mg of Na monoiodoacetate (MIA). Four of the 8 horses were not treated (controls), and 4 horses were treated by intra-articular injection of 250 mg of PSG into both middle carpal joints once a week for 5 treatments starting 1 week after cartilage injury. Horses were maintained for 8 weeks. There was less joint circumference enlargement in PSG-treated horses in MIA-injected and physical defect carpi, compared with that in controls. In MIA-injected joints, there was less articular cartilage fibrillation and erosion, less chondrocyte death, and greater safranin-O staining for glycosaminoglycans in PSG-treated horses. Evaluation of joints in which physical defects were made revealed no differences between control and PSG-injected joints. None of the partial-thickness defects had healed. Full-thickness defects were repaired with fibrous tissue (which was more vascular and cellular in PSG-injected joints) and occasionally small amounts of fibrocartilage. Seemingly, PSG had chondroprotective properties in a model of chemically induced articular cartilage damage, whereas PSG had no obvious effect in a physical articular cartilage-defect model.     

In vitro evaluation of the effect of dimethyl sulfoxide on equine articular cartilage matrix metabolism

OBJECTIVE: To evaluate the effects of dimethyl sulfoxide (DMSO) on equine articular cartilage matrix metabolism. STUDY DESIGN: Using a cartilage explant culture system, proteoglycan (PG) synthesis, PG release, lactate metabolism, chondrocyte viability, and metabolism recovery were determined after cartilage exposure to DMSO. SAMPLE POPULATION: Cartilage harvested from metacarpophalangeal and metatarsophalangeal joints of 12 horses (age range, 1 to 10 years). METHODS: Explants were exposed to concentrations of DMSO (1% to 20%) for variable times (3 to 72 hours). PG synthesis and release were determined by a radiolabel incorporation assay and dimethylmethylene blue (DMMB) dye assay, respectively. Lactate released into culture media was measured, and chondrocyte viability was assessed using the Formizan Conversion Assay and a paravital staining protocol. Metabolism recovery was assessed in explants that were allowed to recover in maintenance media after exposure to DMSO. RESULTS: PG synthesis and lactate metabolism were inhibited in a dose- and time-dependent manner after exposure to DMSO concentrations > or = 5%; there was no significant alteration in PG release. No change in chondrocyte viability was detected after incubation with DMSO. PG synthesis and lactate metabolism returned to baseline rates when allowed a recovery period after exposure to DMSO. CONCLUSIONS: DMSO concentrations > or = 5% suppress equine articular cartilage matrix metabolism. Suppression of PG synthesis and lactate metabolism is reversible and does not appear to be the result of chondrocyte death. CLINICAL RELEVANCE: Equine clinicians adding DMSO to intraarticular lavage solutions should be aware that DMSO may have deleterious effects on equine articular cartilage matrix metabolism.     

Effects of intramuscular polysulfated glycosaminoglycan on chemical and physical defects in equine articular cartilage.

The effect of intramuscular polysulfated glycosaminoglycan (PSG) on repair of cartilage injury was evaluated in eight horses. In each horse, one middle carpal joint had both a partial-thickness and a full-thickness articular cartilage defect created. In the contralateral middle carpal joint, chemical articular cartilage injury was created by intra-articular injection of 50 mg sodium monoiodoacetate (MIA). Horses were divided into two groups for treatment. Group 1 horses (control) received an intramuscular injection of normal saline every four days for a total of seven injections starting seven days after cartilage injury. Group 2 horses received 500 mg of PSG intramuscularly every four days for seven treatments starting seven days after cartilage injury. Horses were maintained for 12 weeks. Horses were evaluated clinically, and their middle carpal joints were evaluated radiographically and arthroscopically at the end of the study. Joint tissues were also collected and examined microscopically. The only significant difference between groups was slightly greater matrix staining intensity for glycosaminoglycans in the radiate articular cartilage layer in MIA injected and PSG treated joints. Partial-thickness defects had not healed and the predominant repair tissue in full-thickness defects was fibrous tissue. It was concluded that using this joint injury model, 500 mg PSG administered intramuscularly had no effect on the healing of articular cartilage lesions, and minimal chondroprotective effect from chemically induced articular cartilage degeneration.     

Effects of sodium hyaluronate and methylprednisolone acetate on proteoglycan synthesis in equine articular cartilage explants

OBJECTIVE: To determine effects of sodium hyaluronate (HA) on corticosteroid-induced cartilage matrix catabolism in equine articular cartilage explants. SAMPLE POPULATION: 30 articular cartilage explants from fetlock joints of 5 adult horses without joint disease. PROCEDURE: Articular cartilage explants were treated with control medium or medium containing methylprednisolone acetate (MPA; 0.05, 0.5, or 5.0 mg/mL), HA (0.1, 1.0, or 1.5 mg/mL), or both. Proteoglycan (PG) synthesis was measured by incorporation of sulfur 35-labeled sodium sulphate into PGs, and PG degradation was measured by release of radiolabeled PGs into the medium. Total glycosaminoglycan (GAG) content in media and explants and total explant DNA were determined. RESULTS: Methylprednisolone acetate caused a decrease in PG synthesis, whereas HA had no effect. Only the combination of MPA at a concentration of 0.05 mg/mL and HA at a concentration of 1.0 mg/mL increased PG synthesis, compared with control explants. Methylprednisolone acetate increased degradation of newly synthesized PGs into the medium, compared with control explants, and HA alone had no effect. Hyaluronate had no effect on MPA-induced PG degradation and release into media. Neither MPA alone nor HA alone had an effect on total cartilage GAG content. Methylprednisolone acetate caused an increase in release of GAG into the medium at 48 and 72 hours after treatment. In combination, HA had no protective effect on MPA-induced GAG release into the medium. Total cartilage DNA content was not affected by treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Our results indicate that HA addition has little effect on corticosteroid-induced cartilage matrix PG catabolism in articular cartilage explants.     

Differences in the topographical distribution of articular cartilage degeneration between equine metacarpo- and metatarsophalangeal joints

REASONS FOR PERFORMING STUDY: The equine metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints, although having virtually the same geometrical appearance, differ in the prevalence of joint pathologies, such as osteochondral fragmentation, and in biomechanical behaviour. The recently developed cartilage degeneration index (CDI) technique offers a possibility to assess quantitatively differences in cartilage degeneration between these joints and to compare these with known differences in biomechanics and clinical observations. OBJECTIVES: To compare the topographical distribution of articular cartilage degeneration across the proximal articular surface of the proximal phalanx (P1) in the equine fore- and hindlimb. METHODS: In 24 distal hindlimbs from 24 horses, articular cartilage degeneration of the proximal articular surface of P1 was quantified using the CDI. Overall CDI value (CDI(P1)) and CDI values of 6 areas of interest were determined: the medial dorsal surface (mds), lateral dorsal surface (lds), medial central fovea (mcf), lateral central fovea (lcf), medial plantar surface (mps) and lateral plantar surface (lps). The joints were divided into 4 equally sized groups of increasing CDI(P1) values. From an existing CDI database of MCP joints, 24 joints were selected with matching CDI(P1) values to the MTP joints and CDI values for the same areas of interest were determined. RESULTS: In both the MCP and MTP joints, highest CDI values were determined at the dorsal articular surfaces. Values were not significantly different between fore- and hindlimbs. In contrast to the MCP joint, CDI values at the plantar joint margin were significantly higher compared to CDI values in the central sites in the MTP joint. CDI values for the plantar surfaces of P1 were significantly higher than those for the palmar surfaces in the forelimb in joints with advanced stages of OA; and values for the central regions of P1 were significantly lower in the hindlimb compared with the forelimb in joints with severe OA. CONCLUSIONS: In both fore- and hindlimbs, initial cartilage degeneration started at the dorsal articular margin of P1. There was a major difference in the spread of cartilage degeneration; in the forelimb both the central and palmar parts are about equally involved, whereas in the hindlimb the plantar parts were significantly more and the central parts significantly less involved. These differences can be linked to differences in biomechanical loading reported elsewhere. POTENTIAL RELEVANCE: This study supports the hypothesis that differences in biokinematics between fore- and hindlimbs are associated with differences in the development of cartilage degeneration and other joint pathologies such as osteochondral fragmentation in the MCP and MTP joints. This information is indispensable for a better understanding of the dynamic nature and progression of these joint disorders and may be of help when monitoring the effects of therapeutic interventions and preventative measures.     

Effects of radial shock waves on membrane permeability and viability of chondrocytes and structure of articular cartilage in equine cartilage explants

OBJECTIVE: To investigate in vitro effects of radial shock waves on membrane permeability, viability, and structure of chondrocytes and articular cartilage. SAMPLE POPULATION: Cartilage explants obtained from the third metacarpal and metatarsal bones of 6 horses. PROCEDURE: Equine cartilage was subjected to radial shock waves and then maintained as explants in culture for 48 hours. Treatment groups consisted of a negative control group; application of 500, 2,000, and 4,000 impulses by use of a convex handpiece (group A); and application of 500, 2,000, and 4,000 impulses by use of a concave handpiece (group B). Effects on explant structure were evaluated by use of environmental scanning electron microscopy (ESEM). Membrane permeability was determined by release of lactate dehydrogenase (LDH). Chondrocyte viability was assessed by use of vital cell staining. Comparisons of LDH activity and nonviable cell percentages were performed by ANOVA. RESULTS: Cell membrane permeability increased significantly after application of 2,000 and 4,000 impulses in groups A and B. A significant decrease in cell viability was observed for application of 4,000 impulses in explants of group A. There was no detectable damage to integrity of cartilage explants observed in any treatment group by use of ESEM. CONCLUSIONS AND CLINICAL RELEVANCE: Radial shock waves do not appear to structurally damage articular cartilage but do impact chondrocyte viability and membrane permeability. Caution should be exercised when extremely high periarticular pulse doses are used until additional studies can determine the long-term outcome of these effects and appropriate periarticular treatment regimens can be validated.     

In vitro stimulation of equine articular cartilage proteoglycan synthesis by hyaluronan and carprofen.

The effects of hyaluronan and carprofen (both racemic mixture and separate R and S enantiomers) on proteoglycan (PG) synthesis by equine cultured chondrocytes and cartilage explants were examined. Hyaluronan stimulated PG synthesis in both cell and explant cultures. The concentration-response curve of the latter was bell-shaped. Racemic carprofen and R and S enantiomers also stimulated PG synthesis, although concentration-response relationships varied for each preparation and high concentrations inhibited synthesis. It was concluded that (a) hyaluronan exerts a stimulatory effect on PG synthesis at low concentrations and (b) stimulatory effects of carprofen on PG synthesis are, to some degree, enantioselective with the carprofen S-enantiomer exerting the greatest effect. Hyaluronan and carprofen are used clinically despite incompletely understood mechanisms of action. These results suggest (a) hyaluronan and carprofen might exert an anti-arthritic action through stimulation of PG synthesis and (b) there is possible justification for therapeutic administration of enantiomeric rather than racemic carprofen.     

Validation of magnetic resonance imaging for measurement of equine articular cartilage and subchondral bone thickness

OBJECTIVE: To validate use of magnetic resonance images (MRIs) for measurement of equine articular cartilage and subchondral bone thickness by comparison with measurements in histologic specimens. SAMPLE POPULATION: 32 cadaveric carpal joints from 16 horses. PROCEDURE: Magnetic resonance imaging was performed by use of 3-dimensional fast spoiled gradient echo (SPGR) and T2* 3-dimensional fast gradient echo (GRE) pulse sequences with and without fat saturation. Standard sites on the medial and lateral facets of the intermediate, radial, and third carpal bones were used for subchondral bone and articular cartilage thickness measurements. Digital image analysis software was used for MRI measurements 10 mm from the dorsal extent and perpendicular to the articular surface. Histomorphometric measurements of hyaline, calcified cartilage, and subchondral bone thickness were obtained at selected sites. Comparisons between histomorphometric and MRI measurements and between magnetic resonance pulse sequences were evaluated. RESULTS: There were significant correlations between GRE and SPGR and SPGR and histologic measurements of articular cartilage, with no significant difference between measurements and good agreement. When calcified cartilage was excluded from the histologic measurement, MRI measurements were significantly greater than histologic measurements. For subchondral bone thickness, there was significant correlation between GRE and SPGR but GRE was significantly greater than SPGR measurements. Histomorphometric and MRI measurements were strongly correlated and not significantly different. CONCLUSIONS AND CLINICAL RELEVANCE: Magnetic resonance imaging provides a good representation of cartilage and subchondral bone thickness, supporting its use in the study and clinical diagnosis of osteochondral structure and alteration.     

The distribution of cartilage oligomeric matrix protein (COMP) in equine carpal articular cartilage and its variation with exercise and cartilage deterioration

Based on previous studies where tendons receiving the most load have been shown to have the highest levels of cartilage oligomeric matrix protein (COMP), we hypothesized that COMP distribution in articular cartilage may be influenced by mechanical loading. This investigation aimed (a) to describe the pattern of COMP immunoreactivity in middle carpal joint cartilage of two-year-old Thoroughbred horses; (b) to determine topographical variations; (c) to compare high (group 1) and low (group 2) intensity training and (d) to describe COMP immunoreactivity at sites with early osteoarthritis.Group 1 (n =6) underwent a 19 week high-intensity treadmill training programme and group 2 (n =6) were given daily walking until euthanasia. Dorsal and palmar sites on radial and third carpal articular surfaces were prepared. Immunohistochemistry was performed with polyclonal rabbit anti-equine COMP antiserum using a biotin-streptavidin/peroxidase method. Results showed: (a) intracellular immunoreactivity was present in all cartilage zones, but the distribution of COMP staining within the matrix varied between cartilage zones; (b) differences in distribution between sites were not observed, but total COMP levels in exercised horses (n =2) did vary between sites with dorsal sites containing less COMP than palmar sites on the radial, intermediate and third carpal lateral facet; (c) group 1 cartilage showed marked interterritorial distribution in the deep layer compared to group 2 where staining was more generalized throughout the matrix and (d) fibrillated cartilage showed increased local immunoreactivity in the matrix. These findings demonstrate zonal variations in equine COMP distribution which may be influenced by loading.     

Ultrastructural immunolocalization of cartilage oligomeric matrix protein (COMP) in the articular cartilage on the equine third carpal bone in trained and untrained horses

The present study was designed to delineate the presence of COMP at the ultrastructural level comparing concentrations between two areas of articular cartilage from the equine third carpal bone, subjected to different loading, from trained and untrained horses. We also analyzed the fibril thickness of collagen type II in the same compartments and zones. Samples were collected from high load-bearing areas of the dorsal radial facet (intermittent high load) and an area of the palmar condyle (low constant load) in five non-trained and three trained young racehorses. The data show that COMP is much less abundant in the matrix in intermittent high loaded areas of articular cartilage from trained horses as compared to the untrained horses (p = 0.036). On the other hand, the untrained horses often displayed a higher immunolabeling in loaded areas compared to unloaded areas, indicating that an adequate dynamic load promotes COMP synthesis and/or retention, while an excessive load may have an opposite effect. The collagen fibril diameter showed marked variation between individuals. The present study indicates that dynamic in vivo compression at high load and frequency lowers matrix content of COMP in the articular cartilage of the third carpal bone. It also indicates that the collagen network is influenced by mechanical load following by strenuous exercise.     

Influence of age on the disposition kinetics of chloramphenicol in equine neonates

The effect of age on the pharmacokinetics of chloramphenicol was determined after IV administration of chloramphenicol sodium succinate (25 mg/kg of body weight) to 6 foals at 1 day and 3, 7, 14, and 42 days of age. The disposition of chloramphenicol was best described, using a two-compartment open model in all foals at all ages evaluated. Significant age-related changes were observed in values for the major kinetic terms describing the disposition of chloramphenicol in foals; the greatest changes were observed between 1 day and 3 days of age. The mean +/- SD value for elimination rate constant (beta) for chloramphenicol in 1-day-old foals (0.131 +/- 0.06 h-1) was significantly (P less than 0.005) lower than the value in 3-day-old foals (0.514 +/- 0.156 h-1), and both values were significantly (P less than 0.05) lower than values for beta in 7-, 14-, and 42-day-old foals. With increasing age, the increase in the mean value for beta resulted in decrease in the harmonic mean elimination half-time (t1/2 beta) for chloramphenicol, from 5.29 hours in 1-day-old foals to: 1.35 hours in 3-day-old foals; 0.61 hour in 7-day-old foals; 0.51 hour in 14-day-old foals; and 0.34 hour in 42-day-old foals. At 1, 3, and 7 days of age, values for t1/2 beta of chloramphenicol in a premature foal born after parturition was induced with oxytocin, were considerably longer than comparable t1/2 beta values for term foals born naturally.(ABSTRACT TRUNCATED AT 250 WORDS)