The effects of intrathecally administered alpha 2 agonists on somato-sympathetic reflex

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We studied the analgesic and cardiovasucular effect of intrathecally administered alpha 2 adrenoceptor agonists, clonidine and medetomidine, using somato-sympathetic reflex as a parameter. Concerning for clonidine, intravenous administration was studied and the same parameters were also evaluated.(Method)Somato-sympathetic reflex potentials (A and C reflex potentials) which were derived from lumbar sympathetic ganglion of cats by electrical stimulation of femoral nerve were induced. Alpha-2 agonists were administered from intrathecally implanted PE-10 catheter or intravenous line in the forearm.(Result)1. Intrathecal administeration of clonidine(1) Decreased A reflex potential proved that clonidine makes a role of hypotention and bradycardia.(2) Decreased C reflex potential indicates that clonidine act as an analgesic by central mechanism involving spinal cord.2. Intravenous administeration of clonidine(1) Intravenously applied clonidine also showed similar results as intrathecal clonidine.(2) Temporal hypertension observed in high dose of clonidin was thought to be elicited by activation of alpha 1 or alpha 2 receptors in peripheral vasculature.3. Intrathecally applied medetomidine also affects sympathetic reflex potentials and act as an analgesic by central mechanism involving spinal cord.