Pain
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Comparative Study
Are mechanical and cold allodynia in mononeuropathic and arthritic rats relieved by systemic treatment with calcitonin or guanethidine?
The putative antinociceptive action of guanethidine and calcitonin systemically injected has been compared in 2 rat models of persistent experimental pain: Freund's adjuvant-induced arthritis (n = 29) and mononeuropathy induced by 4 loose ligatures around the sciatic nerve (n = 24). Guanethidine (30 mg/kg, i.v.) and calcitonin (0.125 mg, s.c.) were injected once a day over 1 week, when hyperalgesia was fully developed. ⋯ Guanethidine treatment was ineffective on hyperalgesia exhibited in arthritic rats but was able to reduce reliably and even suppress the abnormal reactions to cold stimulus in neuropathic animals. The lack of hypoalgesic action of calcitonin versus its beneficial action in bone repair, as well as the possible role(s) of the sympathetic system in neuropathic versus arthritic pain and in hyperalgesia versus physical signs of inflammation, are discussed.