Background: Increased tendon production of the inflammatory mediator prostaglandin E2 (PGE2) has been\r\nsuggested to be a potential etiologic agent in the development of tendinopathy. Repeated injection of PGE2 into\r\ntendon has been proposed as a potential animal model for studying treatments for tendinopathy. In contrast,\r\nnonsteroidal anti-inflammatory drugs (NSAIDs) which inhibit PGE2 production and are commonly prescribed in\r\ntreating tendinopathy have been shown to impair the healing of tendon after acute injury in animal models. The\r\ncontradictory literature suggests the need to better define the functional effects of PGE2 on tendon. Our objective\r\nwas to characterize the effects of PGE2 injection on the biomechanical and biochemical properties of tendon and\r\nthe activity of the animals. Our hypothesis was that weekly PGE2 injection to the rat patellar tendon would lead to\r\ninferior biomechanical properties.\r\nMethods: Forty rats were divided equally into four groups. Three groups were followed for 4 weeks with the\r\nfollowing peritendinous injection procedures: No injection (control), 4 weekly injections of saline (saline), 4 weekly\r\ninjections of 800 ng PGE2 (PGE2-4 wks). The fourth group received 4 weekly injections of 800 ng PGE2 initially and\r\nwas followed for a total of 8 weeks. All animals were injected bilaterally. The main outcome measurements\r\nincluded: the structural and material properties of the patellar tendon under tensile loading to failure, tendon\r\ncollagen content, and weekly animal activity scores.\r\nResults: The ultimate load of PGE2-4 wks tendons at 4 weeks was significantly greater than control or saline group\r\ntendons. The stiffness and elastic modulus of the PGE2 injected tendons at 8 weeks was significantly greater than\r\nthe control or saline tendons. No differences in animal activity, collagen content, or mean fibril diameter were\r\nobserved between groups.\r\nConclusions: Four weekly peritendinous injections of PGE2 to the rat patellar tendon were not found to be an\r\neffective model of clinical tendinopathy. In contrast, improved structural and material properties of the patellar\r\ntendon were found after PGE2 injection. While PGE2 has been thought to have a contributory role in the\r\ndevelopment of tendinopathy and anti-inflammatory medications remain a common treatment, our results suggest\r\na positive role of PGE2 in tendon remodeling in some circumstances.
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