Opioid, calcium, and adrenergic receptor involvement in protopine analgesia.
The analgesic effect of protopine (Pro), an alkaloid isolated from Papaveraceae, was confirmed by tail-pinch and hot-plate tests when given sc 10-40 mg.kg-1, and 20-40 mg.kg-1 inhibited the spontaneous movements of mice. Pro 40 mg.kg-1 increased the sleeping rate, prolonged the sleeping duration, and shortened the sleeping latency in mice hypnotized by ip pentobarbital sodium 30 mg.kg-1. Pro 10-40 mg.kg-1 did not affect the inflammatory reaction induced by xylene and egg white. An icv injection of Pro 20-200 micrograms/mouse showed a remarkable analgesic effect in mice. The icv pretreatment of naloxone 2 micrograms blocked the analgesic effect completely. CaCl2 40 micrograms/mouse (ICV) or methotrexate 10 mg.kg-1 (ip), an agonist of Ca2+ channel, showed a complete blockade of the analgesia, while nifedipine 100 mg.kg-1(po), a blocker of Ca2+ channel, enhanced the analgesic effect. The ip pretreatment of reserpine 4 mg.kg-1 reduced the Pro analgesia. Phentolamine 10 mg.kg-1(ip), an alpha-adrenergic blocker, tended to weaken the analgesia, but propranolol 10 mg.kg-1(ip), a beta-blocker, did not affect it. These results suggest that Pro displays its analgesic effect mainly through the opioid and calcium systems and partly through the adrenergic mechanism.
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Department of Pharmacology of Chinese Materia Medica, China Pharmaceutical University, Nanjing.
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Wu
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D000470:Alkaloids / Q000302:isolation & purification / Q000494:pharmacology*; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D053119:Benzophenanthridines; D001600:Berberine Alkaloids; D004365:Drugs, Chinese Herbal / Q000737:chemistry; D005260:Female; D008727:Methotrexate / Q000494:pharmacology; D051379:Mice; D008813:Mice, Inbred ICR; D009270:Naloxone / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D017288:Pain Threshold / Q000187:drug effects; D010646:Phentolamine / Q000494:pharmacology; D012110:Reserpine / Q000494:pharmacology
D000470:Alkaloids; D000700:Analgesics; D053119:Benzophenanthridines; D001600:Berberine Alkaloids; D004365:Drugs, Chinese Herbal; D009270:Naloxone; D012110:Reserpine; D009543:Nifedipine; C009093:protopine; D008727:Methotrexate; D010646:Phentolamine