Antidiabetic activity of Vatairea macrocarpa extract in rats
Introduction
Diabetes mellitus is a metabolic disorder characterized by hyperglycemia and carbohydrate, protein and fat metabolism disturbances. Causes can be poor glycemia regulation of insulin secretion and/or diminished insulin signaling in key tissues (such as the liver) resulting in post-prandial or fasting/post-prandial hyperglycemia. More evident symptoms are post-prandial sickness due to hyperglycemia, increased food ingestion due to loss of appetite control, muscular proteolysis and adipose tissue lipolysis leading to severe body weight loss, glycosuria and osmotic polyuria, etc. Since causes can be spread between pancreatic, hepatic and peripheral tissues, combined treatments are a forthcoming choice: according to epidemiologic studies in USA, more than 30% of diagnosed diabetic patients are more than 30 years old and may receive insulin, 55% may receive another treatment (Harris, 1995).
In Brazil, due to poverty and limited access to health services, almost all population has made use of medicinal plants at least once (Teixeira et al., 2006). Therefore, traditional knowledge should be used for learning the pharmacological actions of plants commonly used in treating different diseases. In the region of Cuiaba, State of Mato Grosso, traditional knowledge of plant-usage is now restricted mostly to more than 60 year old people, in whom the reported incidence of diabetes reaches 18% (8% of the total population). Furthermore only 20% of medicinal plants used still are wild species coming from the savanna (Voeks, 2004).
The Vatairea macrocarpa (Benth) Ducke (Leguminoseae) is a native wild tree of Brazilian savanna and widely distributed over all Brazilian territory. It has valuable timber and is commonly known as Amargoso for its bitter taste and also as maleiteira and Angelim-do-Cerrado in central savanna as well as in eastern parts of the country. The V. macrocarpa's tea is extensively used in folk medicine to treat diabetes symptoms, as well as other diseases (Guarim Neto and Morais, 2003, Carvalho, 2004). Traditional usage often recommends boiling a piece of stem bark from which a bitter reddish-brown tea is obtained with a 2.5% (w/w) extraction yield. The beneficial effects on glucose homeostasis of other species of the Leguminosae family popularly used as anti-diabetic have been verified (Silva et al., 2002, Fuentes et al., 2004, Ojewole and Adewonmi, 2004).
Effects on lymphocytes by a lectin isolated from seeds of V. macrocarpa have been reported (Martinez et al., 2004), and its inhibitory action on inflammatory response to several stimuli was also shown (Alencar et al., 2003, Alencar et al., 2004). There are however no scientific studies on anti-diabetic effects of V. macrocarpa. In this investigation, the anti-diabetic effect of ethanol extract of stem-bark of V. macrocarpa on normal and streptozotocin diabetic rats is reported.
Section snippets
Materials and methods
The experimental protocol was approved by the Ethics Committee of the Federal University of Mato Grosso, Mato Grosso State, Brazil.
Results
Doses of 250 and 500 mg/kg were chosen for sub-chronic experiments from a previous Hyppocratic test (Malone, 1983) of doses ranging from 250 to 5000 mg/kg of extract administered a single time to non-diabetic fed mice (male and female). The doses used are respectively 1/20 and 1/10 of the lower dose in which behavior alterations were observed (5000 mg/kg), yet without any mortality.
In diabetic rats administration of 500 mg/kg of extract for 22 days reduced post-prandial glycemia (Fig. 1A, p < 0.01).
Discussion and conclusion
Long-term administration of 500 mg/kg of ethanol extract of V. macrocarpa showed significant anti-diabetic effects, decreased post-prandial glycemia but not fasting blood glucose (Fig. 1, Fig. 2, t = 0). Decreased post-prandial glucose in these animals may be linked to decreased glyconeogenic activity suggested by reduced urea excretion and stimulation of glycogenesis and/or inhibition of glycogenolysis, suggested by increased liver glycogen. This latter effect is completely ascribed to increased
Acknowledgements
We thank the technicians Marlene Mariano, Salete Ozaki and Libério Neto for their help and Msc. Harri Lourenzi of the Plantarum Institute for identification and authentication of Vatairea macrocarpa. We are also grateful for the support given by the Coordination of Improvement of University Level personnel (CAPES), support by Research Foundation of Mato Grosso (FAPEMAT) and National Research Council (CNPq) for financial support.
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