Introduction Tendons or regions within a tendon are subjected to tension, compression, friction or a combination thereof. The first aim of this study was¹ to analyse the morphology and expression of extracellular matrix genes in six different regions of the Achilles tendon complex of intact normal rabbits. Men and women experience tendon conditions/injuries with different frequency (Cook, 2007; Cook, 1998; Taunton, 2002). Oestrogen receptors or their transcripts have been detected in human muscles (Wiik, 2009), ligaments (Liu, 1996) and rabbit tendons (Hart, 1998; 2005), making hormones a potential influencer of tendon injury and healing. The second aim² was to assess the effect of ovariohysterectomy (OVH) on the regional expression of these genes.

Methods Female New Zealand White rabbits were divided in two groups¹ intact normal rabbits (n = 4) and² OVH rabbits (n = 8). For each rabbit, the Achilles tendon complex was dissected into six regions: distal gastrocnemius (DG), distal flexor digitorum superficialis (DFDS), proximal lateral gastrocnemius (PLG), proximal medial gastrocnemius (PMG), proximal flexor digitorum superficialis (PFDS), and paratenon. For each of the regions, hematoxylin and eosin staining was performed for histological evaluation of intact normal rabbit tissues and mRNA levels for proteoglycans, collagens and genes associated with collagen regulation were assessed by RT-qPCR for both the intact normal and OVH rabbit tissues.

Results The distal regions displayed a more fibrocartilaginous phenotype. For intact normal rabbits, aggrecan mRNA expression was higher in the distal regions of the Achilles tendon complex compared to the proximal regions. Collagen Type I and MMP-2 expression levels were increased in the PLG compared to the DG in the intact normal rabbit tissues. The tendons from OVH rabbits had lower gene expressions for the proteoglycans aggrecan, biglycan, decorin and versican compared to the intact normal rabbits, although the regional differences of increased aggrecan expression in distal regions compared to proximal regions persisted.

Discussion The tensile and compressive forces experienced in the examined regions may be related to the regional differences found in gene expression. The lower mRNA expression of the genes examined in the OVH group confirms a potential effect of systemic oestrogen on tendon.

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Hart, et al . Clin Orthop Rel Res.1998;351:44–56, 1998

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