Actions of intrathecal chloroprocaine and sodium bisulfite on rat spinal reflex function utilizing a noninvasive technique.

An in situ electrophysiologic technique was developed to study the effects of intrathecal chloroprocaine and sodium bisulfite on spinal reflex activity in the anesthetized rat. By not surgically invading the subarachnoid space, this procedure allows drugs to be administered remotely through an indwelling catheter while monitoring drug effects on the spinal monosynaptic reflex with noninvasive electrophysiologic methods. In this way the normal pharmacokinetic factors are left intact so that time-action relations can be monitored under conditions that may resemble spinal anesthesia in conscious animals. Using this technique it was established that chloroprocaine with and without 0.2% sodium bisulfite blocks the monosynaptic reflex in a fully reversible manner. The reflex block of a higher concentration of bisulfite (0.6%) was poorly reversible in some preparations. These results correlate well with a previous in vivo behavioral study on the motor and sensory blocking actions of intrathecal chloroprocaine and bisulfite in the same animal species. The authors feel this technique can be used to study the temporal changes in reflex activity caused by other drugs administered via the intrathecal route.