Studies on the antiinflammatory,immunoregulatory, and analgesic actions of melatonin

In order to develop melatonin (MT) as a potential new drug for the treatment of diseases with inflammation, pain, and abnormal immune responses, the effects and mechanisms of MT on inflammation, immunoregulation, and nociception were studied systematically. MT (40–160 mg/kg, ip) had significant analgesic effects in the hot-plate, writhing, and tail-flick models, with a marked dose- and time-dependence. The onset of its analgesia about 30–60 min after ip, was slower than that of pethidine, but the duration was longer (about 1.5–2 h). The analgesia was also induced by icv MT (0.25 mg/kg) injection. A lower dose of MT (10 mg/kg) could enhance the analgesic effect of pethidine, which was blocked by naloxone (10 mg/kg). MT (100 mg/kg, ip) decreased the content of beta-endorphin in the hypothalamus and pituitary. The analgesia of MT could be attenuated by pretreatment with reserpine (30 mg/kg, ip) or phentolamine (10 mg/kg, ip). CaCl₂ (230 mg/kg) could antagonize the analgesia of MT. EGTA and verapamil had opposite effects to CaCl₂. No tolerance and dependence to MT was found in mice. Further studies showed that MT could enhance the functions of T and B lymphocytes and macrophages in vitro and in adjuvant arthritis, and inhibit the disturbance of immune cells. MT could inhibit the swelling of hindpaw induced by carrageenin and complete Freund's adjuvant. These factors suggest that MT possesses marked antiinflammatory, immunoregulatory, and analgesic effects which may be related to the system of opiate, monoamine, and Ca²⁺ modulation. Drug Dev. Res. 39:167–173. © 1997 Wiley-Liss, Inc.     

A long-form α-neurotoxin from cobra venom produces potent opioidindependent analgesia

AIM: In light of the antinociceptive activity of the short-chain neurotoxin, cobrotoxin, and other acetylcholine antagonists, the antinociceptive activity and mechanisms of cobratoxin (CTX), a long-chain postsynaptic alpha-neurotoxin, was investigated in rodent pain models. METHODS: CTX was administered intraperitoneally (30, 45, 68 microg/kg), intra-cerebral ventricularly (4.5 microg/kg) or microinjected into periaqueductal gray (PAG; 4.5 microg/kg). The antinociceptive action was tested using the hot-plate and acetic acid writhing tests in mice and rats. The involvement of the cholinergic system and opioid system in CTX-induced analgesia was examined by pretreatment of animals with atropine (0.5 mg/kg, im; or 10 mg/kg, ip) or naloxone (1 and 5 mg/kg, ip). The effect of CTX on motor activity was tested using the Animex test. RESULTS: CTX exhibited a dose-dependent analgesic action in mice as determined by both the hot-plate and acetic acid writhing tests. The peak effect of analgesia was seen 3 h after administration. In the mouse acetic acid writhing test, the intra-cerebral ventricular administration of CTX at 4.5 microg/kg (1/12th of a systemic dose) produced marked analgesic effects. Microinjection of CTX (4.5 microg/kg) into the PAG region did not elicit an analgesic action in rats in the hot-plate test. Atropine at 0.5 mg/kg (im) and naloxone at 1 and 5 mg/kg (ip) both failed to block the analgesic effects of CTX, but atropine at 10 mg/kg (ip) did antagonize the analgesia mediated by CTX in the mouse acetic acid writhing test. Acetylsalicylic acid (300 mg/kg) did not enhance the analgesic effects of CTX. At the highest effective dose of 68 microg/kg the neurotoxin did not change the spontaneous mobility of mice. CONCLUSION: CTX has analgesic effects, which are mediated in the central nervous system though not through the PAG. The central cholinergic system but not opioid system appears to be involved in the antinociceptive action of CTX.     

The interaction of morphine and meperidine with the analgesic, convulsant, and lethal properties of lidocaine in mice.

Because of increased intravenous use of lidocaine in medicine, a study was undertaken to evaluate the interaction of the commonly used narcotics, morphine and meperidine, with the analgesic, convulsant, and lethal properties of lidocaine in male Swiss-Webster mice. An analgesic response (Eddy hot plate test) was defined as a reaction time that was at least twice the control time. Equipotent doses of morphine and meperidine were determined by measuring the analgesic response 30 min after ip administration. The dose that produced analgesia in 25% of the mice (AD25) for morphine was 3.9 mg/kg and for meperidine was 24 mg/kg. Thereafter the mice were evaluated with three drug combinations: lidocaine and saline, lidocaine p;us the AD25 of morphine, and lidocaine plus the AD25 of meperidine. The morphine-lidocaine and meperidine-lidocaine combinations were equally effective in increasing the analgesic properties of lidocaine. However, only the meperidine-lidocaine drug combination significantly decreased the median convulsive dose (CD50) and the median lethal dose (LD50) of lidocaine alone. By comparing the ratios of the CD50/AD50 and the LD50/AD50 for the morphine-lidocaine and meperidine-lidocaine drug combinations, it can be concluded that the meperidine-lidocaine interaction, because of its increased toxicity, is a less favourable combination.     

褪黑素和哌替啶的耐受性及对小鼠脾淋巴细胞增殖反应的影响

采用热板法测定小鼠痛阈，发现ｉｐ褪黑素（ＭＴ）４０ｍｇ·ｋｇ－１·ｄ－１连续６ｄ，镇痛作用持续、明显；ｉｐ哌替啶４０ｍｇ·ｋｇ－１·ｄ－１连续６ｄ，镇痛作用逐渐减弱，至ｄ６时已无镇痛作用。ｄ７ｉｐＭＴ和哌替啶同上剂量１ｈ时测定小鼠ＣｏｎＡ诱导的脾淋巴细胞增殖反应，发现ＭＴ能明显提高淋巴细胞增殖反应，而哌替啶对小鼠脾淋巴细胞增殖反应有抑制趋向。结果提示：ＭＴ不同于哌替啶无耐受性，且能促进脾淋巴细胞功能。     

Opiate and acetylcholine-independent analgesic actions of crotoxin isolated from crotalus durissus terrificus venom.

The venom of Crotalus durissus terrificus is reported to have analgesic activity and the administration of Crotoxin (Cro) to cancer patients is reported to reduce the consumption of analgesics. This study investigated the analgesia induced by Cro and the effects of atropine and naloxone on the antinociceptive activity of Cro in mice and rats. The results showed that Cro at 66.5, 44.3 and 29.5microg/kg (ip) exhibited a dose-dependent analgesic action in mice using the hotplate and acetic acid writhing tests. Cro at 44.3microg/kg (ip) had significant analgesic action in the rat tail-flick test. In the mouse acetic acid-writhing test, intracerebral ventricular administration of Cro 0.3microg/kg produced marked analgesic effects. Microinjection of Cro (0.15microg/kg) into the periaqueductal gray area also elicited a robust analgesic action in rat hotplate test. Atropine at 0.5mg/kg (im) or 10mg/kg (ip) or naloxone at 3mg/kg (ip) failed to block the analgesic effects of Cro. These results suggest that Cro has analgesic effects mediated by an action on the central nervous system. The muscarinic and opioid receptors are not involved in the antinociceptive effects of Cro.     

利血平与优降宁对动物痛阈和吗啡镇痛作用影响因素探讨

采用三种测痛方法,观察了利血平、优降宁对小鼠、大鼠正常痛阈和吗啡镇痛作用的影响,结果表明:ip利血平2 mg/kg,优降宁100 mg/kg均能明显抑制小鼠扭体反应;ip利血平1 mg/kg能明显提高小鼠热板反应时间,但ip优降宁75 mg/kg无明显影响;ip利血平6 mg/kg,优降宁75 mg/kg对大鼠甩尾反应时间均无明显影响;利血平(小鼠0.5～1.0 mg/kg,大鼠2 mg/kg ip)能明显对抗吗啡镇痛作用;优降宁(小鼠35 mg/kg,大鼠50 mg/kg ip)能明显增强吗啡镇痛作用,并能“逆转”利血平对抗吗啡镇痛作用。其“逆转”作用的强弱取决于利血平、优降宁给药的先后次序。     

利血平与优降宁对动物痛阈和吗啡镇痛作用影响因素探讨

采用三种测痛方法,观察了利血平、优降宁对小鼠、大鼠正常痛阈和吗啡镇痛作用的影响,结果表明:ip利血平2 mg/kg,优降宁100 mg/kg均能明显抑制小鼠扭体反应;ip利血平1 mg/kg能明显提高小鼠热板反应时间,但ip优降宁75 mg/kg无明显影响;ip利血平6 mg/kg,优降宁75 mg/kg对大鼠甩尾反应时间均无明显影响;利血平(小鼠0.5～1.0 mg/kg,大鼠2 mg/kg ip)能明显对抗吗啡镇痛作用;优降宁(小鼠35 mg/kg,大鼠50 mg/kg ip)能明显增强吗啡镇痛作用,并能“逆转”利血平对抗吗啡镇痛作用。其“逆转”作用的强弱取决于利血平、优降宁给药的先后次序。     

Salmon calcitonin potentiates the analgesia induced by antidepressants

Antidepressants are used in the treatment of a variety of pain syndromes. Most of them act by blocking noradrenaline (NA) and serotonin (5-HT) reuptake. It is also well known that the serotonergic system is also involved in calcitonin (CT) analgesia. Taking these two evidences into account, the modification of the analgesic effect of nortriptyline, amitriptyline, and paroxetine in the presence of salmon CT (s-CT) was examined in mice. The forced-swimming test was carried out in order to choose doses of each drug that did not induce an antidepressant effect under our experimental conditions (nortriptyline: 0.2-5 mg/kg ip, amitriptyline: 2.5-20 mg/kg ip, and paroxetine: 5-30 mg/kg ip). The analgesic effect of each antidepressant was then evaluated using the acetic acid test. At the doses tested, the antidepressants induced a dose-dependent analgesic effect. When mice were pre-treated with a subanalgesic dose of s-CT (2.5 IU/kg), the analgesic effect of amitriptyline and paroxetine was significantly increased though no modification was found for nortriptyline. In summary, s-CT was able to increase the analgesic effect of the antidepressant drugs that reduce the uptake of 5-HT, suggesting that the joint administration of antidepressants and CT may be an interesting alternative in pain management.     

褪黑素镇痛的相关机制

目的　探讨褪黑素 (MT)镇痛作用与内源性阿片肽、去甲肾上腺素能神经系统及钙通道的关系。方法　大鼠和小鼠痛阈的测定采用热板法 ;β 内啡肽 (β EP)的测定采用放免法 (RIA)。结果　松果腺切除后d 8大鼠痛阈的昼夜节律性消失 ,icvMT 0 2 5mg·kg-1可出现明显的镇痛作用 ;ipMT(10 0mg·kg-1) 1h后下丘脑、垂体 β EP含量均明显降低 ;ip利血平 (3mg·kg-1)可使MT镇痛作用消失 ,而sc酚妥拉明 (10mg·kg-1)可减弱MT的镇痛作用 ;CaCl2 (2 30mg·kg-1)与MT(40mg·kg-1)合用时 ,可使MT的镇痛作用减弱 ,EGTA (180mg·kg-1)及维拉帕米 (15mg·kg-1)则可使之加强。结论　MT的镇痛作用可能与内源性阿片肽、去甲肾上腺素能神经系统及Ca2 + 通道等有关