Neurotensin-induced antinociception in mice: antagonism by thyrotropin-releasing hormone.
Neurotensin (NT), administered intracisternally to mice, produced significant dose-dependent antinociception in three analgesic tests: tail immersion, hot-plate and acetic acid writhing. Naloxone (1-5 mg/kg), an opiate antagonist administered i.p. 20 min before NT administration, did not significantly alter NT-induced antinociception in any of these tests; naloxone did significantly reverse beta-endorphin-induced antinociception. However, centrally and peripherally administered thyrotropin-releasing hormone antagonized NT-induced (but not beta-endorphin-induced) antinociception. Equimolar doses of another tripeptide (Pro-Leu-Gly-NH2; melanostatin) did not alter the effects of NT. The data obtained in this study confirm NT-induced antinociception, provide further evidence that NT does not activate naloxone-sensitive opiate receptors and demonstrate that this brain effect of NT is antagonized by thyrotropin-releasing hormone. These findings therefore support the hypothesis that NT and thyrotropin-releasing hormone are functional antagonists in the central nervous system.
D000700:Analgesics; D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D009075:MSH Release-Inhibiting Hormone / Q000494:pharmacology; D008297:Male; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D009496:Neurotensin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011930:Reaction Time / Q000187:drug effects; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D000700:Analgesics; D009270:Naloxone; D009496:Neurotensin; D013973:Thyrotropin-Releasing Hormone; D009075:MSH Release-Inhibiting Hormone