Journal of Pharmacology and Toxicology1816-496x2152-100xAcademic Journals Inc.10.3923/jpt.2006.259.269Abdel SalamOmar M.E. El-BatranSiham BaiuomyAyman R. 3200613The anti-nociceptive effect of melatonin on visceral pain evoked by i.p. acetic acid injection in mice was investigated. Melatonin (1-8 mg kg-1, s.c.) caused a dose-dependent inhibition of the acetic acid-induced writhes (by 84 to 98.6%). The inhibition of writhing response by melatonin (4 mg kg-1) was not reduced by co-administration of theα-2 adrenoceptor antagonist yohimbine (4 mg kg-1, i.p.). In contrast, the α-1 adrenoceptor antagonist doxazocin (16 mg kg-1, s.c.) reduced the anti-writhing effect of melatonin, whereas the α 1-adrenoceptor antagonist prazosin (2 mg kg-1, i.p.) was without effect. The effect of melatonin was slightly reduced by beta-adrenoceptor blockade with propranolol (2 mg kg-1, i.p.) or adrenergic neuron blockade with guanethidine (8 or 16 mg kg-1, i.p.). The muscarinic receptor antagonist atropine (2 mg kg-1 i.p.), the potassium channel blocker glibenclamide (5 mg kg-1, i.p.), the opioid antagonist naloxone (5 mg kg-1, i.p.) or the non-selective adenosine receptor antagonist, theophylline (10 mg kg-1 i.p.), failed to reduce the anti-writhing effect of melatonin. The antinociceptive effect of melatonin was slightly reduced by co-administration of the central dopamine D2 receptor antagonist sulpiride (15 mg kg-1, i.p.) (though not by haloperidol, 2 mg kg-1, i.p.) and to more extent by the dopamine D2 receptor agonist bromocryptine (1.5 mg kg-1, i.p.), whereas metoclopramide (3 mg kg-1, i.p.), chlorpromazine (3 mg kg-1, i.p.), domperidone (10 mg kg-1, i.p.) or blockade of dopamine D1 receptors by clozapine (5 mg kg-1, i.p.) had no effect. In conclusion, melatonin exerts potent anti-nociceptive effects on visceral pain in mice. The antinociception caused by melatonin is subject to modulation by noradrenergic and dopaminergic neural pathways.]]>Al-Chear, E.D. and R.J. Traub,200296221225Allegra, M., R.J. Reiter, D.X. Tan, C. Gentile, L. Tesoriere and M.A. Livrea, 200334110Ben-Sreti, M.M., J.P. Gonzalez and R.D. Sewell, 198333665668Cervero, F. and J.M. Laird, 20033608612Cuzzocrea, S., G. Costantino, E. Mazzon and A.P. Caputi, 199927914Dunwiddie, T.V. and S.A. Masino,2001243155El-Shenawy, S.M., O.M.E. Abdel-Salam, A.R. Baiuomy, S. El-Batran and M.S. Arbid,200246235243Frussa-Filho, R., J.B. Rocha, I.M. Conceicao, C.F. Mello and M.E. Pereira, 19963317493Ghelardini, C., N. Galeotti and A. Bartolini, 200082130137Gleeson, R.M. and D.M. Atrens, 198278141146Gutierrez, T., A.G. Nackley, M.H. Neely, K.G. Freeman, G.L. Edwards and A.G. Hohmann, 2003987176185Koster, R., M. Anderson and E.J. de Beer,195918412412Kowaluk, E.A., J. Mikusa, C.T. Wismer, C.Z. Zhu and E. Schweitzer et al.,2000In vivo characterization in the rat. ]]>29511651174Laurido, C., T. Pelissie, R. Sotomoyano, L. Valladares, F. Flores and A. Hernandez,2002138991Li, D.P., S.R. Chen, Y.Z. Pan, A.I. Levey and H.L. Pan, 2002543807818Messner, M., G. Huether, T. Lorf, G. Ramadori and H. Schworer, 200269543551Michael-Titus, A., R. Bousselmame and J. Costentin, 1990187201207Noseda, R., A. Hernandez, L. Valladares, M. Mondaca, C. Laurido and R. Soto-Moyano, 20043604144Ohkubo, Y., K. Nomura and I. Yamaguchi, 1991204121125Paalzow, G.H., 19942528797Reiter, R.J., 199516383415Rodriguez, C., J.C. Mayo, R.M. Sainz, I. Antolin, F. Herrera, V. Martin and R.J. Reiter, 20043619Rooney, K.F. and R.D. Sewell, 1989168329336Sawynok, J.,1998347111Serpell, M., 200565255Silva, S.O., M.R. Rodrigues, S.R. Carvalho, L.H. Catalani, A. Campa and V.F. Ximenes, 200437171175Takeshita, N. and I. Yamaguchi, 1997281315321Tanabe, M., K. Takasu, N. Kasuya, S. Shimizu, M. Honda and H. Ono, 2005144703714Yu, CX., C.B. Zhu, S.F. Xu, X.D. Cao and G.C. Wu,2000282161164Zhang, H.M., D.P. Li, S.R. Chen and H.L. Pan, 2005313697704Zimmermann, M.,198316109110