Conde Garcia E A, Nascimento V T, Santiago Santos A B
Laboratório de Biofísica dos Tecidos Excitáveis, Departamento de Fisiologia, Centro de Ciências Biológicas e da Saúde, Universidade Federal de Sergipe, São Cristóvão, SE, Brasil.
Braz J Med Biol Res. 2003 May;36(5):661-8. doi: 10.1590/s0100-879x2003000500014. Epub 2003 Apr 22.
Many pharmacological effects have been ascribed to extracts of Psidium guajava L. (guava) leaves. However, in spite of its widespread use in Brazilian folk medicine and a reasonable number of scientific reports about it, we could not find any study dealing with its action on the mammalian myocardium. In the present study, by measuring isometric force, we observed that the crude extract of P. guajava (water-alcohol extract obtained by macerating dry leaves) depresses the guinea pig atrial contractility in a concentration-dependent fashion (N = 8 hearts, 15 trials). The compound with cardiac activity was concentrated by extraction in a Soxhlet apparatus using 17 M glacial acetic acid after removing the less polar fractions (hexane, chloroform, acetone, ethanol and methanol), suggesting that this compound is a highly polar substance. In the isolated guinea pig left atrium the acetic acid fraction (10-800 mg/l) of P. guajava 1) reversibly decreased myocardial force in a concentration-dependent fashion (EC50 = 0.07g/l, N = 5 hearts, 9 trials, P<0.05), 2) increased the atrial relaxation time measured at 20% of the force amplitude up to 35% (91 +/- 15 to 123 +/- 30 ms, N = 3 hearts, 6 trials, P<0.05), 3) abolished the positive staircase effect (Bowditch phenomenon) in a concentration-dependent fashion suggesting a decrease of the cellular inward calcium current (N = 4 hearts, 8 trials, P<0.05), and 4) its inotropic effect was abolished by cholinergic receptor blockade with 1.5 mM atropine sulfate, indicating a cholinergic involvement in the mechanism of action of the extract (N = 7 hearts, 15 trials, P<0.05). The acetic acid extract was 20 times more potent than crude extract (EC50 = 1.4 g/l). The results showed that extracts from P. guajava leaves depress myocardial inotropism.
番石榴叶提取物具有多种药理作用。然而，尽管其在巴西民间医学中广泛应用且有不少相关科学报道，但我们未能找到任何关于其对哺乳动物心肌作用的研究。在本研究中，通过测量等长力，我们观察到番石榴粗提取物（由干燥叶片浸渍得到的水 - 醇提取物）以浓度依赖性方式抑制豚鼠心房收缩力（N = 8 颗心脏，15 次试验）。在去除极性较小的馏分（己烷、氯仿、丙酮、乙醇和甲醇）后，使用 17 M 冰醋酸在索氏提取器中进行提取，从而浓缩出具有心脏活性的化合物，这表明该化合物是一种高极性物质。在分离的豚鼠左心房中，番石榴的醋酸馏分（10 - 800 mg/l）：1）以浓度依赖性方式可逆地降低心肌力（EC50 = 0.07 g/l，N = 5 颗心脏，9 次试验，P<0.05）；2）将在力幅值 20%时测量的心房舒张时间增加高达 35%（从 91 ± 15 到 123 ± 30 ms，N = 3 颗心脏，6 次试验，P<0.05）；3）以浓度依赖性方式消除正阶梯效应（鲍迪奇现象），提示细胞内向钙电流降低（N = 4 颗心脏，8 次试验，P<0.05）；4）其变力作用被 1.5 mM 硫酸阿托品的胆碱能受体阻断所消除，表明提取物的作用机制涉及胆碱能（N = 7 颗心脏，15 次试验，P<0.05）。醋酸提取物的效力比粗提取物高 20 倍（EC50 = 1.4 g/l）。结果表明，番石榴叶提取物可抑制心肌收缩力。
