Effect of Immature Rubus occidentalis on Postoperative Pain in a Rat Model

Background and Objectives: This study aimed to identify the analgesic properties of immature Rubus occidentalis extract (iROE) using a postoperative-pain rat model. We also aimed to compare the analgesic effects of iROE to those of mature R. occidentalis extract (mROE) and examine the proinflammatory cytokine response and associated underlying mechanisms. Materials and Methods: In adult male Sprague Dawley rats, acute postoperative pain was induced through plantar hind-paw incisions. After the plantar incisions were made, the rats were intraperitoneally administered with normal saline or various doses of iROE and mROE to investigate and compare the analgesic effects of iROE and mROE. The mechanisms underlying iROE-induced analgesia were investigated via post-incisional administration of yohimbine, dexmedetomidine, prazosin, naloxone, atropine, or mecamylamine, followed by iROE. Mechanical withdrawal threshold (MWT) evaluations with von Frey filaments were carried out at different time points. Serum levels of tumor necrosis factor α, interleukin (IL)-1β, and IL-6 were measured to assess inflammatory responses. Multivariate analysis of variance (MANOVA) and linear mixed-effects model (LMEM) analysis were used to analyze the analgesic effect data. Results: The MWTs demonstrated significant increases in iROE in a dose-dependent manner up to 2 h after the plantar incisions were made. An LMEM analysis demonstrated that iROE yielded a significantly greater analgesic effect than mROE, but there was no significant difference between the two according to MANOVA. Dexmedetomidine enhanced the MWT-confirmed iROE response, while yohimbine and naloxone diminished it. Administration of iROE significantly attenuated the post-incisional increases in serum IL-1β and IL-6 levels. Conclusions: The iROE demonstrated analgesic and anti-inflammatory effects in a rat model of incisional pain, which were more pronounced than those associated with mROE. The analgesic activity of iROE may be associated with α₂-adrenergic and opioid receptors.