Mechanical hyperalgesia is attenuated by local administration of octreotide in pristane-induced arthritis in Dark-Agouti rats

AimsThe Dark-Agouti (DA) rat is very susceptible to pristane-induced arthritis (PIA) and represents a suitable model for rheumatoid arthritis. In the present study, we examined the pain sensitivity and the effect of local administration of octreotide (OCT) on mechanical hyperalgesia in PIA DA rats.Main methodsArthritis was induced by intradermal injection of pristane (300 µl). The mechanical withdrawal threshold (MWT) and heat withdrawal latency (HWL) were used to evaluate the pain sensitivity. In addition, we recorded the discharge firings in the tibial nerve sensory C-fibers innervating the inflamed toe joints of arthritic DA rats.Key findingsTwo weeks after injection of pristane, all DA rats developed severe arthritis. This symptom was associated with a decreased MWT (78.50 ± 5.68 mN before pristane injection, 19.50 ± 6.27 mN on day 14 after pristane injection), indicating a mechanical hyperalgesia in PIA. In contrast, HWL was comparable before and after pristane injection (10.25 ± 0.70 s before injection; 9.45 ± 1.23 s on day 14 after injection). Local injection of OCT markedly increased MWT and relieved the hyperalgesia in PIA. In addition, OCT significantly decreased the discharge rate of afferent C units evoked by both non-noxious and noxious joint movements.SignificanceTaken together, the results demonstrate that mechanical hyperalgesia, but not thermal hyperalgesia is associated with PIA and that the mechanical hyperalgesia and the discharge of afferent C units are attenuated by local administration of OCT. These observations provide evidence for a novel therapeutic strategy for pain control in rheumatoid arthritis.