Opioid, calcium, and adrenergic receptor involvement in protopine analgesia
Xu, Q.; Jin, R.L.; Wu, Y.Y.
Zhongguo Yao Li Xue Bao 14(6): 495-500
1993
ISSN/ISBN: 0253-9756 PMID: 8010045 Document Number: 421333
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 cntdot kg-1, and 20-40 mg cntdot kg-1 inhibited the spontaneous movements of mice. Pro 40 mg cntdot kg-1 increased the sleeping rate, prolonged the sleeping duration, and shortened the sleeping latency in mice hypnotized by ip pentobarbital sodium 30 mg cntdot kg-1. Pro 10-40 mg cntdot kg-1 did not affect the inflammatory reaction induced by xylene and egg white. An icv injection of Pro 20-200 mu-g/mouse showed a remarkable analgesic effect in mice. The icv pretreatment of naloxone 2 mu-g blocked the analgesic effect completely. CaCl-2 40 mu-g/mouse (icv) or methotrexate 10 mg cntdot kg-1 (ip), an agonist of Ca-2+ channel, showed a complete blockade of the analgesia, while nifedipine 100 mg cntdot kg-1 (po), a blocker of Ca-2+ channel, enhanced the analgesic effect. The ip pretreatment of reserpine 4 mu-g cntdot kg-1 reduced the Pro analgesia. Phentolamine 10 mg cntdot kg-1 (ip), an alpha-adrenergic blocker, tended to weaken the analgesia, but propranolol 10 mg cntdot 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.