ABSTRACT
To study whether commercial traditional Chinese medicinal preparations Injection Paederiae (IP) or Injection Stauntonia (IS) has anti-nociceptive and/or anti-inflammatory effects, we used two persistent pain models (bee venom and formalin test) to evaluate the systemic effects of IP or IS on the chemical tissue injury-induced persistent spontaneous pain-related responses (PSPR), primary thermal/mechanical hyperalgesia and inflammation in conscious rats. Injection of bee venom (BV, 0.1 mg, 50 microl) into the plantar surface of one hind paw resulted in not only a 1-h monophasic PSPR such as flinching reflex in the injected paw and a subsequent period of 3-4 days primary heat and mechanical hyperalgesia, but also a marked sign of inflammation, including redness and swelling of the plantar surface in the injected paw. Intraplantar injection of formalin produced two phases of PSPR as reported previously. Systemic pre-treatment with three doses of IP (0.32, 1.6 and 9.0 ml/kg, 500%) or IS (0.32, 1.6 and 9.0 ml/kg, 250%) produced a dose-dependent suppression of the BV- or formalin-induced flinching reflex of 1 h time course as compared with the saline control group. Post-treatment with IP or IS 5 min after BV injection also produced a significant suppression of the flinching reflex in both BV test and formalin test respectively, as compared with the control group. However, neither pre- nor post-treatment with IP or IS produced any significantly suppressive effect on the BV-induced primary heat and mechanical hyperalgesia and inflammation. The analgesia produced by IP or IS was not mediated by the endogenous opioid receptors since naloxone, a non-selective opioid receptor antagonist, had no reversal effect on the IP and IS-produced analgesia in the BV-induced PSPR. Our present results suggest that IP or IS might prevent and relieve clinical persistent spontaneous pain, but without any anti-nociceptive and anti-inflammatory effects on the primary heat hyperalgesia, mechanical hyperalgesia, as well as inflammatory responses. The BV test might be a useful model of pain to evaluate and screen anti-nociceptive and anti-inflammatory effects of certain compounds of the Chinese medicinal herbs on the pathological origins of pain.