Effect of prostaglandin E2 injection on the structural properties of the rat patellar tendon

Abstract

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

HGF Mediates the Anti-inflammatory Effects of PRP on Injured Tendons

“…However, the complete suppression of PGE 2 production is not desirable, since under normal conditions, tendons contain a basal level of PGE 2 [44]. This PGE 2 may play an important role in tendon remodeling [51].…”

Use of an IL1‐receptor antagonist to prevent the progression of tendinopathy in a rat model

“…Both patellar tendons were injected with the knee flexed using a 27‐guage needle inserted halfway between the origin and insertion of the patellar tendon and aiming for the proximal aspect of the tendon at the distal pole of the patella. A similar method had previously been performed at this institution and practiced with dye on cadaver limbs to ensure injection into the correct location . CON animals received injections containing 100 microliters of phosphate‐buffered saline (PBS).…”

“…10,11 One such model employs the use of carrageenan, a natural inflammatory substance that increases IL1-b and TNF-a levels, and has previously been used for screening new anti-inflammatory, and analgesic agents. 5,12,13 Carrageenan injections have been used to establish tendinopathy in both the rat Achilles and rotator cuff tendons (16,22). 14 Tillander et al used carrageenan injected into the rat subacromial bursa to successfully reproduce tendinopathy related changes in the supraspinatus tendon.…”

The use of an IL1‐receptor antagonist to reverse the changes associated with established tendinopathy in a rat model

“…Each animal’s knee was flexed, and the patellar tendon was injected using a 27‐guage needle inserted halfway between the origin and insertion of the patellar tendon while aiming for the proximal aspect of the tendon. This method has previously been performed by this study group and practiced with dye on cadaver limbs to ensure correct placement . The IL1‐RA dosage used in this study corresponds with dosages previously administered locally in rat inflammation models as well as in the previous study by this group .…”