Dual actions of substance P on nociception: possible role of endogenous opioids.
Substance P produces analgesia when administered to mice in very small doses by the intraventricular route (1.25 to 5 nanograms per mouse). The analgesic effect can be blocked by naloxone. At higher doses (greater than 50 nanograms per mouse), this activity is lost. At these higher doses, however, substance P produced hyperalgesia when combined with naloxone and analgesia when combined with baclofen [beta-(4-chlorophenyl)-gamma-aminobutyric acid]. Substance P may have dual actions in brain, releasing endorphins at very low doses and directly exciting neuronal activity in nociceptive pathways at higher doses.
D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000494:pharmacology*; D004745:Enkephalins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D011957:Receptors, Opioid / Q000187:drug effects*; D013329:Structure-Activity Relationship; D013373:Substance P / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D004723:Endorphins; D004745:Enkephalins; D011957:Receptors, Opioid; D013373:Substance P; D009270:Naloxone; D001418:Baclofen