HYPERALGESIA INDUCED BY LOW-DOSES OF THYMULIN INJECTIONS - POSSIBLE INVOLVEMENT OF PROSTAGLANDIN E(2)

Thymulin injection into rats (20-150 ng) i.p. caused a significant red uction in both mechanical (paw pressure test) and thermal (hot plate a nd tail flick tests) nociceptive thresholds. Thymulin injection also d oubled IL-1 beta level in the liver of these animals. Induced hyperalg esia was reversed completely by alpha-MSH related tripeptide, Lys-D-Pr o-Val in low doses, which is known to antagonize IL-1 beta and PGE(2) induced hyperalgesia, but was only partly reversed by IL-1 beta relate d tripeptide, Lys-D-Pro-Thr at high doses, which is known to antagoniz e IL-1 beta induced hyperalgesia only. We conclude from these results that thymulin causes hyperalgesia and that this effect is at least in part mediated via PGE(2) and its effectiveness at low concentration im plies a physiological role for this thymic hormone.