Background: Medicinal plants contain physiologically active principles that over the years have been exploited in traditional medicine for the treatment of various ailments. Objectives and Methods: This study aimed to investigate the effects of the methanolic extract of Pausinystalia yohimbe bark (5 mg/ml) on isolated rabbit aortic strip and rat uterus. Results: methanolic extract of P. yohimbe bark (5 mg/ml) produced relaxation of the phenylephrine precontracted-rabbit aortic strip. This relaxation may be resulted through nitric oxide (NO), since the pretreatment of the isolated rabbit aortic strip with methylene blue inhibited the NO-mediated relaxation. Moreover, the extract exhibited relaxation of rat uterine muscles, which appeared to be not mediated by activation of β2-adrenoceptors and/or H2 receptors, since the relaxant effect continued even after the pretreatment of the tissue with propranolol and ranitidine respectively. Conclusion: The obtained results revealed that methanolic extract of P. yohimbe bark caused relaxation of both isolated rat uterus and rabbit aortic strip through facilitating the role of endogenous compounds such as NO.
 Tchoundjeu, Z., Ngo Mpeck, M.L., Asaah, E. and Amougou, A. (2004) The role of vegetative propagation in the domestication of Pausinystalia johimbe (K. Schum), a highly threatened medicinal species of West and Central Africa. Forest Ecology and Management, 188, 175-183. doi:10.1016/j.foreco.2003.07.010
 Khosravi, M., Oryan, S., Haeri Rohani, S.A., Parivar, K. and Marandi, R. (2006) Control of environmental health and removal of rats by α2-adrenergic antagonists and potassium channel blocker. Iranian Journal of Environmental Health Science and Engineering, 3, 255-260.
 Brunton, L., Keith, P., Donald, B. and Iain, B. (2008) Goodman and Gilman’s manual of pharmacology and therapeutics. Drugs acting at synaptic and neuroeffector junctional sites. 11th Edition, McGraw-Hill Medical Publishing Division, New York.
 Zanolari, B. (2003) Natural aphrodisiacs. Studies of commercially-available herbal recipes, and phytochemical investigation of Erythroxylum Vacciniifolium Mart. (Erythroxylaceae) from Brazil. Ph.D. Thesis, University of Lausanne, Lausanne.
 Murburg, M.M., Villacres, E.C., Ko, G.N. and Veith, R.C. (1991) Effects of yohimbine on human sympathetic nervous system function. Journal of Clinical Endocrinology and Metabolism, 73, 861-865. doi:10.1210/jcem-73-4-861
 Furchgott, R.F. and Bhadrakom, S. (1953) Reactions of strips of rabbit aorta to epinephrine, isopropylarterenol, sodium nitrate and other drugs. Journal of Pharmacology and Experimental Therapeutics, 108, 129-143.
 Dacquet, C., Mirranneu, C. and Mirranneu, J. (1987) Effects of calcium entry blockers on calcium dependent contraction of rat portal vein. British Journal of Pharmacology, 92, 203-211. doi:10.1111/j.1476-5381.1987.tb11313.x
 Ikunobu, M., Tsuyoshi, O., Shigeru, K., Shigeki, H. and Masafumi, O. (1990) Pharmacological sub-classification of α1-adrenoceptors in vascular smooth muscle. British Journal of Pharmacology, 99, 197-201. doi:10.1111/j.1476-5381.1990.tb14678.x
 Marriot, J.F. (1988) A comparison of the effects of the calcium entry blockers verapamil, diltiazem and flunarizine against contractions of the rat isolated aorta and portal vein. British Journal of Pharmacology, 95, 145-154. doi:10.1111/j.1476-5381.1988.tb16558.x
 Janssens, S.P., Shimouchi, A. and Quertermous, T. (1992) Cloning and expression of a cDNA encoding human endothelium-derived relaxing factor/nitric oxide synthase. Journal of Biological Chemistry, 267, 14519.
 Finkel, R., Richard, C., Michelle, A. and Cubeddu, L.X. (2009) Lippincott’s illustrated reviews: Pharmacology. Drugs affecting the autonomic nervous system. 4th Edition, Lippincott Williams and Wilkins, Philadelphia.
 Dasan, L., Sheela, D. and Steven, R.V. (1995) Effects of methylene blue and LY83583 on neuronal nitric oxide synthase and NADPH-diaphorase. European Journal of Pharmacology Section, 290, 247-251. doi:10.1016/0922-4106(95)00084-4
 Hozeifa, M.H., Imad, M.T., Elhadi, M.M., Abd Elwahab, H.M. and Nizar, S. (2012) Effects of methanolic extract of Pausinystalia yohimbe bark on blood glucose level in normal fasting rats. Journal of Health, 4, 1225-1228. doi:10.4236/health.2012.412180
 Digges, K.G. and Summers, R.J. (1983) Characterization of postsynaptic α-adrenoceptors in rat aortic strips and portal veins. British Journal of Pharmacology, 79, 655- 665. doi:10.1111/j.1476-5381.1983.tb10002.x
 Jensen, K.B. and Vennerod, A.M. (1961) Reversal of the inhibitory action of adrenaline and histamine on rat uterus. Acta Pharmacologica et Toxicologica, 18, 307-312. doi:10.1111/j.1600-0773.1961.tb01672.x
 Bertaccini, G., Molina, E., Vitali, T. and Zappia, L. (1979) Actions of histamine receptor agonists and antagonists on the rat uterus. British Journal of Pharmacology, 66, 13- 17. doi:10.1111/j.1476-5381.1979.tb16091.x
 Rosic, M., Guozden, R., Zorica, L., Suzana, P. and Rajko, L. (2005) Effects of phenylethylamine on isolated uterus in rats treated with estrogen. Jugoslovenska Medicinska Biohemija, 24, 265-270. doi:10.2298/JMB0504265R