The presence of calcium channel blocker(s) in turmeric A.H. Gilani, M.N. Ghayur, K. Majeed, F. Shaheen and A.J. Shah. Department of Biological and Biomedical Sciences, The Aga Khan University Medical College, Karachi, Pakistan.

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Curcuma domestica rhizome, commonly known as "Turmeric", is a widely used spice and food additive in different parts of the world. Besides its domestic use, it is employed by the traditional healers in an array of gastrointestinal and respiratory disorders, such as anorexia, abdominal pains, diarrhoea, asthma, cough and hepato-biliary disorders (Fleming et al., 1998). Turmeric and its main constituent, curcumin, have been reported to exhibit a variety of pharmacological activities (Ammon & Wahl 1991), but the precise mechanism of action for modulating smooth muscle tone is not identified. In this investigation we describe the presence of calcium channel blocking activity in turmeric and curcumin, which may explain some of the folkloric uses of the plant particularly in gastrointestinal and respiratory disorders.

Fresh turmeric rhizomes (430 g) were cleaned, ground and then macerated at room temperature in 70% aqueous-methanol for 3 days thrice. The combined filtrate was dried in a Rotary Evaporator to yield 19 g of thick, brown coloured crude extract. Curcumin was obtained from Sigma Chemicals Ltd. USA. Segments of rabbit jejunum, rat stomach fundus, guinea-pig ileum, colon, and trachea were suspended separately in 10 ml tissue baths, containing Krebs or Tyrode's solution at 37°C and aerated with a mixture of 5 % carbon dioxide in oxygen. Responses were recorded on Grass Polygraph.

The plant extract dose-dependently (0.03-0.3 mg ml^-1) relaxed the spontaneous contractions of the rabbit jejunum, with EC50 values of 0.18 ± 0.02 mg/ml (mean ± s.e.m.; n=5). When tested against high K⁺ (80 mM)-induced contraction, it caused a dose-dependent inhibition at similar doses suggestive of calcium channel blockade (CCB). The CCB activity was confirmed when the crude extract dose-dependently (0.03-0.3 mg ml^-1) shifted the Ca⁺⁺ dose-response curves in jejunum, constructed in a Ca⁺⁺ free medium, to the right (Bolton, 1979). Similarly, it caused inhibition of agonist-induced contractions in rat stomach fundus and guinea-pig ileum, colon and tracheal preparations in a non-specific manner indicating the presence of general spasmolytic activity, a typical characteristic of calcium antagonists. When curcumin was tested for its possible spasmolytic activity, it exhibited inhibitory effect both in spontaneous and high K⁺(80 mM)-induced contractions in isolated rabbit jejunum preparations suggestive of calcium channel blockade (Bolton, 1979). The inhibitory effect was dose-dependent, mediated in the dose range of 1-30 µM. In the acute toxicity test, the extract was devoid of any apparent toxic effect up to the dose of 3 g kg^-1.

These data indicate that turmeric and its known active ingredient curcumin exhibit spasmolytic activity possibly through blockade of calcium influx and this activity may explain some of its folkloric uses, such as, abdominal cramps, diarrhoea and asthma.

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