Intrathecal propranolol displays long-acting spinal anesthesia with a more sensory-selective action over motor blockade in rats

To prevent cardiovascular effects of peripherally administered propranolol, the aim of this study was to evaluate the spinal anesthetic effect of propranolol, a Na± channel blocker. After rats were injected with drugs intrathecally, the spinal anesthetic effect of propranolol was compared with that of lidocaine, which is known to produce local anesthesia. We also evaluated the effect of the addition of clonidine with propranolol on spinal anesthesia. Our results showed that propranolol produced a dose-dependent spinal blockade in motor, proprioception, and nociception. On a 50% effective dose (ED50) basis, the spinal anesthetic effect of propranolol in motor, proprioception, and nociception [1.16 (1.01–1.34), 1.10 (0.92–1.31), 1.05 (0.89–1.24)] was equal to lidocaine [1.03 (0.94–1.13), 0.95 (0.84–1.07), 0.87 (0.79–0.96)], respectively. On an equipotent basis (0.5, 1.0, 2.5 μmol), the sensory/nociceptive block duration caused by propranolol was longer than that caused by lidocaine (P ≤ 0.01). Co-administration of propranolol (1.1 μmol) and clonidine (0.5 μmol) produced greater spinal anesthesia than propranolol (1.1 μmol) or clonidine (0.5 μmol) alone. These preclinical findings demonstrated that propranolol produces similar spinal anesthesia to lidocaine and that α2-adrenergic receptors also contribute to improve the quality and duration of the spinal anesthetic effect of propranolol. Propranolol with a more sensory-selective action over motor blockade elicited longer spinal blockade than did lidocaine.