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Curcuminoid compound extracted from turmeric (Curcuma longa Linn) was evaluated for the effect on isolated smooth muscle. In guinea-pig ileum smooth muscle, curcuminoid at the concentration of 12 μg/ml significantly inhibited the contraction induced by acetylcholine (ACh) 5x10-7 M and histamine 5x10·7 M. (Force of contraction was 62.84 ± 4.66% and 75.60 ± 2.77 % of the control respectively) and the effect was prominently observed when the concentration of curcuminoid was increased to 36 μg/ml (force of contraction was 42.79 ± 1.98 % and 44.93 ± 4.33 % of the control). In potassium depolarizing Tyrode solution, curcuminoid 4 μg/ml and 20 μg/ml reduced the contraction induced by calcium chloride (CaCl2) 1.8 mM significantly. The contraction was 63.31 ± 1.80 % and 36.87 ± 3.25 % respectively. The smooth muscle relaxant effect was confirmed in isolated rat uterine smooth muscle, curcuminoid 8 ·μg/ml and 16 μg/ml significantly reduced force and frequency of contraction induced by oxytocin 1 x 10 ·2 IU/ml. Curcuminoid 8 μg/ml produced 54.68 ± 3.34 % force of contraction and 79.09 ± 2.29 % frequency of contraction. Curcuminoid 16 μg/ml caused more relaxation of rat utrerine smooth muscle. (Force of contraction was 42.34 ± 3.16 % and frequency of contraction was 71.18 ± 1.89% ), In acetylcholine (2 μg/ml) induced contraction, curcuminoid 8 μg/ml also reduced force and frequency of contraction. (Force of contraction was 73.01 ± 4.10 % and frequency of contraction was 76.33 ± 3.94 %). The effect could clearly observed when curcuminoid 16 μg/ml was applied. (Force of contraction was 43.38 ± 3.56 %, frequency of contraction was 49.96 ± 5.20 %) Curcuminoid 8 and 16 μg/ml significantly reduced force of contraction induced by KCl 50 mM. (Force of contraction was 57.10 ± 4.92 % and 36.60 ± 2.99 % respectively) The results obtained from this study suggested that curcuminoid produced smooth muscle relaxation effect on isolated guinea-pig ileum and rat uterus by non-specific inhibitory mechanism.
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