CEREBROSPINAL-FLUID NOREPINEPHRINE AND ACETYLCHOLINE CONCENTRATIONS DURING ACUTE PAIN

Painful stimulation increases spinal cord norepinephrine (NE) in anima ls, and spinally released NE induces acetylcholine (ACh) release to ca use analgesia. The purpose of this study was to determine the relation ship between NE and ACh in cerebrospinal fluid (CSF) in sheep and huma ns during painful stimulation. CSF was sampled in anesthetized sheep b efore and during electrical nerve stimulation at an intensity sufficie nt to increase mean arterial pressure 15%-20%. To determine whether sp inally released NE caused ACh release by stimulation of alpha(2)-adren oceptors, seven sheep received intrathecal (IT) idazoxan whereas seven sheep received IT saline before stimulation. To examine the effect of pain on CSF NE and ACh in humans, CSF was sampled in 33 women after a t least 4 h of painful labor and in 22 pregnant women without pain. Pa inful stimulation in sheep increased CSF NE and ACh. IT idazoxan block ed the increase in both NE and ACh. Although mean concentrations of CS F NE and ACh did not differ between parturients with and without pain, there was a significant correlation between NE and ACh concentrations only in those with pain. These data provide evidence in animals for a ctivation of spinal cord noradrenergic-cholinergic systems in response to pain. There is only weak evidence for such activation, however, in women with painful labor.