The partial agonist properties of levocabastine in neurotensin-induced analgesia.
The antihistaminic drug levocabastine is a ligand for the low affinity neurotensin receptor (NTS2). Its intracerebroventricular administration to mice induced a significant analgesia in the writhing test but not in the hot plate test. In the writhing test, levocabastine decreased neurotensin-induced analgesia to a level not significantly different from the effects of levocabastine alone. In the hot plate test, levocabastine had no analgesic effect but completely reversed the neurotensin-induced analgesia. Mepyramine, another antihistaminic drug, did not share these levocabastine effects. Neither levocabastine nor mepyramine modified the colonic temperature or reversed the neurotensin-induced hypothermia. Thus, levocabastine behaves as a partial agonist at neurotensin NTS2 receptors, which are involved in visceral nociception, but not at yet unidentified neurotensin receptors involved in hypothermia.