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In this study, we report for the first time the effects of Acanthus montanus (Acanthaceae) aqueous extract, its fractions and Acanthus sulphate ester (ASE) – a newly isolated sulphate ester, on rat uterus. This in vitro research involved an organ bath containing an isolated unpregnant rat uterus suspended in De Jalons physiological solution and aerated with Carbogen (95%O2 +5% CO2). Following equilibration, the extract, fraction and ASE were individually added to the tissue in the absence and presence of standard antagonists and compared with standard uterine agonists. The responses were recorded on a 2-channel Ugo Basile recorder.

The extract had a biphasic action with an initial relaxation (IC50 =3.00 mM) of spontaneous uterine contractions followed by stimulation (IC50 =0.63 mM) of the same tissue. Its fraction showed both relaxation and contraction depending on the polarity of extraction solvent. 100% methanolic fraction (IC50 = 150.0 µM) and ASE (131.0 µM) contracted the uterus. The IC50s of the other fractions were variable. These stimulatory activities were less than those of PGF2α, acetylcholine, diazoxide, oxytocine and histamine.

The extract, methanolic fraction and ASE were inhibited by phentolamine, prazosin, pyrilamine, indomethacine, verapamil but not atropine. The extract was unaffected by propranolol while tetraethylammonium had slight stimulation. Quinacrine did not affect the extract and MeOH fraction activities. Verapamil was the most potent inhibitor. The involvement of both extracellular and intracellular ionic channels of calcium and potassium were observed; they are probably involved in the mechanism of action of ASE.

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