［摘要］目的：观察在术后不同阶段静脉注射胆碱酯酶抑制剂毒扁豆碱对鼠痛阈的影响，以及静注毒扁豆碱和蛛网膜下腔注射吗啡的药物相互作用。方法：6组SD大鼠，置入蛛网膜下腔和股静脉导管。采用辐射热刺激诱发的鼠腿撤退试验测痛阈，测试分别于术后1～3 h和术后3 d进行。动物分别接受静注毒扁豆碱、蛛网膜下腔注射吗啡及两者联合给药。比较术后1～3 h和3 d各种药物对痛阈的影响、联合给药与单独给药对痛阈的影响。药物的镇痛效应以最大可能效应的百分比(%MPE)表示。结果：毒扁豆碱术后1～3 h静注导致%MPE明显提高；毒扁豆碱与吗啡的联合给药效应在术后早期更明显；小剂量联合给药的镇痛作用明显大于双倍剂量单独给药的镇痛作用；联合给药的测得效应值明显大于估计叠加效应值。结论：胆碱酯酶抑制剂毒扁豆碱在术后早期产生镇痛作用；静注毒扁豆碱与蛛网膜下腔注射吗啡的联合给药呈协同效应。

［中图分类号］R971.91；R965

［文献标识码］A

［文章编号］1007-7669(2000)06-0433-05

Antinociceptive effect of physostigmine and interaction of intravenous physostigmine with intrathecal morphine in rats

CHEN Lian-Hua

(Department of Anesthesiology, The Eye Ear Nose and Throat Hospital, Shanghai Medical University, SHANGHAI 200031, China)

Alexander NEMIROVSKY

(Department of Anesthesiology, Los Angeles Medical Center of the University of South California, CA 90033, USA)

GONG Qin-Yan

(Department of Pharmacology, Shanghai Medical University, SHANGHAI 200032, China)

［ABSTRACT］AIM: To investigate the antinociceptive effect of anticholinesterase agent physostigmine at different postoperative time, and the interaction of intravenous physostigmine with intrathecal morphine in rats. METHODS: Six groups of rats were operated on for intrathecal and intravenous catheterization. Nociceptive responses of hind paws of each animal were measured with “plantar stimulation” test 1-3 h and 3 d postoperatively. Animals received intravenous (iv) physostigmine, intrathecal (ith) morphine, or combination of both. The antinociceptive effect of each group was converted to the percent maximum possible effect (% MPE).RESULTS: Administration of physostigmine 1-3 h after operation resulted in dramatic increase in % MPE. The effects of combinations of iv physostigmine and ith morphine were more pronounced at early postoperative time. The potency of low dose combination was significantly greater than that of double doses of both drugs. The % MPE of the observed effects of all combinations was significantly higher than that of the expected additive effects.CONCLUSION: The antinociception of physostigmine occurs at early postoperative time. The interaction of iv physostigmine with ith morphine indicates their synergistic effect.

［KEY WORDS］physostigmine; morphine; pain measurement; drug synergism

［Ucnumber］R 971.91；R 965

［Document code］A

［Article ID］1007-7669(2000)06-0433-05

Opioids activate opioid receptors and cause analgesia. The effect of opioid receptor activation may ultimately be mediated by some intermediate neurotransmitters. It has been proved that one of the important inhibitory neurotransmitters in response to noxious stimulation is norepinephrine (NE). In sheep and humans, cerebrospinal fluid (CSF) NE and acetylcholine (Ach) concentrations increased after acute painful stimulation^［1］ and intravenous opioid administration^［2］. In human volunteers, intrathecal cholinesterase inhibitor neostigmine caused the increase in CSF Ach concentration, resulted in analgesia and enhanced the effect of opioids injected systemically. It has been hypothesized that either pain stimulation or opioid administration may induce the release of NE which in turn activates the cholinergic neuron in spinal dorsal horn to release Ach and cause analgesia^［4］. Therefore, the current study was designed to investigate the antinociceptive effect of anticholinesterase agent physostigmine at different postoperative time in rats, and to evaluate the interaction of intravenous (iv) physostigmine with intrathecal (ith) morphine.

MATERIALS AND METHODS

Animal preparationMale, 300-350 g Sprague-Dawley rats were used. Animals were housed individually in a temperature controlled room with a 12 h light-dark cycle, and fed with both food and water available ad libitum. Experiments were performed during the light cycle. Under halothane anesthesia, a chronic catheterization of the lumbar subarachnoid space was performed for the ith injection. Briefly, a PE 10 catheter was inserted through the atlanto-occipital membrane and introduced to a length of 10 cm caudalward into the lumbar subarachnoid space. The catheter was then fixed to the back neck of the animal. A concurrent catheterization of the femoral vein was performed for intravenous injection. The animals which exhibited no signs of neurological deficit after recovery from the anesthesia underwent the experiment procedure.

Nociceptive threshold testNociceptive responses of hind paws of each animal were measured by means of “plantar stimulation” test using a device designed and made by Yaksh's laboratory^［5］ (University of California, San Diego, USA). The rats were placed in a clear plastic cage on an elevated floor of clear glass. To reduce the variability, the under-floor temperature was maintained at 30℃. A radiant heat source from a 50 W, 8 V lamp was contained in a movable holder placed beneath the glass floor. The radiant heat diameter was 4 mm and bulb intensity was controlled at 5.25 A. To initiate a test, the under-floor heat source was positioned to focus at the plantar surface of one hind paw which was completely in contact with the glass. The light was then started meanwhile the timing circuit was initiated automatically. The nociceptive response was determined by the interval from the application of the light beam to the hind paw withdrawal. A cutoff time which was three times of the baseline nociceptive response latency was set in order to avoid tissue burn injury.

Test ProtocolEach rat was used in one dosage regime only. Initially, baseline nociceptive response latency was determined by the average of three measurements. Subsequently, drug administration was performed in a blind fashion. After drug injection, nociceptive response latency of the hind paw was measured at 5 min intervals until the baseline response was regained. The peak time of antinociceptive effect and the duration of the effect were determined. Different groups of rats were scheduled to receive iv physostigmine 50 or 100 μg*kg^-1, ith morphine 1 or 2 μg, or the combinations of iv physostigmine (50 or 100 μg*kg^-1) with concurrent ith morphine 1 μg, respectively. All drugs were dissolved in Ringer's solution and administered in an injection volume of 1 mL*kg^-1 for iv and 10 μL for ith. Following each ith injection, the catheter was flushed with 10 μL Ringer's solution to ensure the drug delivery into ith space. The tests were performed at 1-3 h after the ith and iv catheterization when the rats completely recovered from anesthesia. To compare the antinociceptive effect of each drug in the animals with or without postoperative stress, the tests for the same drug doses were repeated three days later in the same rats.

At the end of the experiments, all rats received an ith injection of 10 μL of 2% lidocaine. Data from rats who did not develop motor paralysis within 2 min