Okwuasaba F, Ejike C, Parry O
J Ethnopharmacol. 1986 Aug;17(2):139-60. doi: 10.1016/0378-8741(86)90054-1.
The skeletal muscle relaxant properties of an aqueous extract of Portulaca oleracea were examined on the twitch and tetanus tension evoked by electrical stimulation using the rat phrenic nerve-hemidiaphragm and frog sciatic nerve-sartorius muscle preparations and on contractures induced by nicotinic agonists using the rat rectus abdominis muscle preparation. The extract (5-50 X 10(-4) g/ml) produced a dose-dependent initial enhancement, followed by a longer lasting depression of twitch tension as induced by indirect electrical stimulation (NS) as well as direct stimulation (MS) of the diaphragm and sartorius muscle preparations. The augmentation of twitch amplitude (MS) produced by the extract was not significantly antagonised or potentiated by d-tubocurarine (5-50 X 10(-8) M) or physostigmine (5-50 X 10(-8) M) at concentrations which blocked or potentiated NS-induced twitch contractions. Furthermore, tetrodotoxin (5 X 10(-7) g/ml) alone or in combination with d-tubocurarine did not significantly attenuate extract-induced augmentation of twitch contractions to MS. In addition, the depression of twitch tension due to NS was not antagonised by physostigmine but was reversed and/or abolished by Ca2+ (2-5 X 10(-3) M) or potassium thiocyanate (1 X 10(-3) M). Contractures induced by K+ (80 mM) or by tetanic stimulation (20-60 Hz) were significantly reduced by the extract whereas, contracture induced by caffeine (2.5-6.0 mM) was not affected. Ca2+-free Tyrode's solution and EDTA (1.25 X 10(-3) g/ml) potentiated extract-induced depression of twitch tension to MS. On the rectus abdominis, contractures induced by nicotinic agonists (acetylcholine, 3-500 X 10(-7) M; carbachol, 5-500 X 10(-7) M and nicotine, 5-500 X 10(-8) M) were significantly attenuated and/or abolished by the extract (5-10 X 10(-3) g/ml). These observations indicate that the aqueous extract possesses unique skeletal muscle relaxant properties which do not appear to involve interference with cholinoceptor mechanism(s). It appears that the mechanism of action of the extract may involve interference with Ca2+ mobilization in skeletal muscle.
利用大鼠膈神经 - 半膈肌和青蛙坐骨神经 - 缝匠肌标本，研究马齿苋水提取物对电刺激诱发的抽搐和强直张力的骨骼肌松弛特性；利用大鼠腹直肌标本，研究其对烟碱激动剂诱发的挛缩的影响。提取物（5 - 50×10⁻⁴ g/ml）对间接电刺激（NS）以及膈肌和缝匠肌标本的直接刺激（MS）所诱发的抽搐张力，呈现出剂量依赖性的初始增强，随后是持续时间更长的抑制作用。提取物所产生的抽搐幅度增强（MS），在能阻断或增强NS诱发的抽搐收缩的浓度下，未被d - 筒箭毒碱（5 - 50×10⁻⁸ M）或毒扁豆碱（5 - 50×10⁻⁸ M）显著拮抗或增强。此外，单独使用河豚毒素（5×10⁻⁷ g/ml）或与d - 筒箭毒碱联合使用，均未显著减弱提取物对MS诱发的抽搐收缩的增强作用。另外，毒扁豆碱未拮抗NS所致的抽搐张力降低，但Ca²⁺（2 - 5×10⁻³ M）或硫氰酸钾（1×10⁻³ M）可使其逆转和/或消除。提取物可显著降低由K⁺（80 mM）或强直刺激（20 - 60 Hz）诱发的挛缩，而对咖啡因（2.5 - 6.0 mM）诱发的挛缩无影响。无Ca²⁺的台氏液和EDTA（1.25×10⁻³ g/ml）增强了提取物对MS诱发的抽搐张力的抑制作用。在腹直肌上，提取物（5 - 10×10⁻³ g/ml）可显著减弱和/或消除烟碱激动剂（乙酰胆碱，3 - 500×10⁻⁷ M；卡巴胆碱，5 - 500×10⁻⁷ M和尼古丁，5 - 500×10⁻⁸ M）诱发的挛缩。这些观察结果表明，该水提取物具有独特的骨骼肌松弛特性，似乎不涉及对胆碱能受体机制的干扰。提取物的作用机制似乎可能涉及对骨骼肌中Ca²⁺动员的干扰。
