Synovial fluid glycosaminoglycan concentration in metacarpophalangeal joint of castrated horses and mares of different ages

Abstract

Total concentration of synovial fluid glycosaminoglycan (GAGs) and a fraction of it (GAGsT) which correspond to different GAGs from hyaluronic acid or sulfated GAGs (GAGsS) that mainly consist of chondroitin sulfate and keratan sulfate, were measured. Samples of synovial fluid were taken from normal metacarpophalangeal joints of crossbred equines immediatelly after slaughter by aseptic needle aspiration. Post mortem joints examination showed that there was no gross evidence of osteoarthritis or other joint disease, based on the appearance of synovial membrane and articular cartilage. Synovial fluid samples were evaluated by its external appearance, protein concentration and mucin clot test. Samples were alloted in four age groups by teeth examination and divided in mares (m) and castrated horses (c.h.) as follows: 1.5 – 2 years (n = 23: 12 m. and 11 c.h.; 4 – 5 years (n = 15: 9 m. and 6 c.h.); 6 – 8 years (n = 23: 13 m. and 10 c.h.) and over 10 years old (n = 17: 12 m. and 5 c.h.). A colorimetric method with Alcian Blue using different electrolyte concentrations was used to quantify these GAGs.

There were no significant differences of GAGsT concentration between mares and castrated horses, but the average of both older groups (> 10 years) was lower (1.71 ± 0.79 mg/ml) than the previous age group (3.39 ± 1.93 mg/ml). The GAGsS content of the synovial fluid, that reflects the catabolic processes of extracellular matrix (MEC) of the articular cartilage, showed no differences between mares and castrated horses in any age group, but these concentrations were always higher in castrated horses. However, the final average of these GAGsS, was higher (p < 0.05) in castrated horses (0.48 ± 0.28 mg/ml) than in mares (0.34 ± 0.15 mg/ml), suggesting a more active degradation of cartilage extracellular matrix in castrated horses. Furthermore, these concentrations tended to decrease from younger to older animals in mares and castrated horses, which could reflect a slower metabolic processes with ageing.

The difference bettween GAGsT and GAGsS represents the concentration of synovial fluid hyaluronic acid, which was lower in the older group of mares (1.62 ± 0.76 mg/ml) and castrated horses (0.96 ± 0.64 mg/ml), suggesting a greater susceptibility to cartilage damage in these animals. These results verify the effect of age or sex condition on synovial fluid GAGs concentration, which could reflect the metabolic status of articular components and therefore, useful for comparison of pathologic conditions.