Dexmedetomidine enhances ultrasound-guided sciatic nerve block in rats by reducing perineural capillary permeability via RhoA/ROCK-MLC signaling

Dexmedetomidine (DEX) is widely used as an adjuvant to local anesthetics to prolong the duration of nerve block-induced analgesia. Despite its clinical efficacy, the precise mechanisms by which DEX enhances and extends analgesic effects remain incompletely understood. An ultrasound-guided rat sciatic nerve block model was established. Twenty four male Sprague-Dawley rats were divided in four groups (n = 6): ropivacaine + dexmedetomidine (ROP + DEX) group; ropivacaine + normal saline (ROP + NS) group; dexmedetomidine + normal saline (DEX + NS) group, and normal saline (NS) group. Analgesic effects were assessed via mechanical and thermal sensitivity testing. Ropivacaine plasma concentrations were determined using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). Capillary permeability was assessed by two-photon intravital imaging using Evans blue dye (EBD) extravasation and Transwell assays. RNA sequencing and Western blotting were performed to identify underlying molecular pathways. The ROP+DEX group demonstrated significantly prolonged analgesia when compared to the ROP+NS group, with an extended t₁/₂ (5.34 h), increased AUC, and a reduced clearance rate (CL), indicating slower systemic absorption of ropivacaine. Two-photon imaging and EBD assays demonstrated reduced perineural capillary leakage. Transwell experiments confirmed that DEX strengthens endothelial barrier integrity. RNA-seq and Gene Ontology (GO) analysis highlighted enrichment in cytoskeletal and adhesion-related pathways, and Western blotting revealed decreased activation of the RhoA/ROCK-MLC signaling pathway in the ROP+DEX group. Dexmedetomidine enhances local anesthetic efficacy by reducing perineural capillary permeability and delaying systemic absorption. This effect is likely mediated through the RhoA/ROCK-MLC signaling pathway, offering a mechanistic basis for its use as an adjuvant in regional anesthesia.