Investigation of Modulation of the Alpha-2 Receptor in Tetrahydropalmatine (THP) Analgesia in Male Sprague-Dawley Rats

Abstract

The increased use of nutraceuticals over the past 20 years makes it essential to know the effects these may have with anesthetics and analgesics (). Tetrahydropalmatine (THP), a derivative of the herb corydalis, may have analgesic properties (; ); however, the mechanism of action is unclear. We proposed that THP may modulate alpha-2 receptors and interact with dexmedetomidine, a known alpha-2-receptor agonist, used for sedation. Fifty-five male Sprague-Dawley rats, divided into five groups, were administered the following by intraperitoneal injection: (1) vehicle, (2) dexmedetomidine, (3) THP, (4) THP and yohimbine, and (5) THP and dexmedetomidine. A baseline measurement of hot-plate latency was recorded, followed by an injection of appropriate compound(s). Testing occurred at 5, 10, 30, and 60 min after injections. Repeated measures ANOVA suggested a significant difference among groups (f = < x > 8.09; < /x > p = < x > 0.00). < i > PosthocBonferronisuggestedthatTHPsignificantlyprolongedreactiontimeonthehotplatecomparedtovehicle < /i > (< /x > p =. 037). Rats injected with THP and yohimbine did not have significantly shorter latency times compared to those injected with THP alone suggesting that THP does not modulate alpha-2 receptors. Finally, rats injected with THP and dexmedetomidine did not demonstrate a significantly increased latency time compared to THP alone, suggesting no additive effect of THP.