Investigation of modulation of the alpha-2 receptor in tetrahydropalmatine (THP) analgesia in male Sprague-Dawley rats.

摘要

The increased use of nutraceuticals over the past 20 years makes it essential to know the effects these may have with anesthetics and analgesics (Kaye et al., 2000). Tetrahydropalmatine (THP), a derivative of the herb corydalis, may have analgesic properties (Hu & Jin, 2000a; Wei, Zou, Young, Dubner, & Ren, 1999); 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=8.09; p=0.00). Post hoc Bonferroni suggested that THP significantly prolonged reaction time on the hot plate compared to vehicle (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.