In situ microdialysis in tendon tissue: high levels of glutamate, but not prostaglandin E-2 in chronic Achilles tendon pain

This investigation was to our knowledge the first to use the microdialysis technique to study concentrations of substances in a human tendon. In four patients (mean age 40.7 years) with a painful nodule in the Achilles tendon (chronic Achilles tendinosis) and in five controls (mean age 37.2 years) w ith normal Achilles tendons (confirmed by ultrasonography) the local concen trations of glutamate and prostaglandin E-2 were measured under resting con ditions. A standard microdialysis catheter was inserted into the Achilles t endon under local anesthesia. Sampling was performed every 15 min over a 4- h period. The results showed significantly higher concentrations of glutama te in tendons with tendinosis than in normal tendons (196 +/- 59 vs. 48 +/- 27 mu mol/l, P < 0.05), and there were no significant changes in glutamate concentration over the period of investigation. There were no significant differences in the mean concentrations of prostaglandin E-2 (83 +/- 22 vs. 54 +/- 24 pg/ml) between tendons with tendinosis and normal tendons. In con clusion, in situ microdialysis appears a useful method to study certain met abolic events in tendon tissue. The higher concentrations of the excitatory neurotransmitter glutamate in Achilles tendons with a painful nodule may p ossibly be involved in the pain mechanism in this chronic condition. Furthe rmore, there were no signs of inflammation in the tendons with painful nodu les, as indicated by the normal prostaglandin E-2 levels.