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Evaluation of the hypoglycemic, hypolipidemic and anti alpha amylase effects of extracts of the twigs and fruits of ficus ovata vahl (moraceae)

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par FOUONDO MAMETOU
University of Yaoundé I - Master 2011
  

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I.1.9.4. Mechanism of action of antidiabetic medicinal plants and their components

There are several possible mechanisms through which these herbs can act to control the blood glucose level (Tanira, 1994). The mechanisms of action can be related, generally, to the ability of the plant in question (or its active principle) to lower plasma glucose level by interfering with one or more of the processes involved in glucose homeostasis. The reported mechanisms whereby herbal antidiabetic remedies reduce blood glucose levels are more or less similar to those of the synthetic oral hypoglycemic drugs and are summarized as follows (Tanira, 1994; Bastaki, 2005; Bnouham et al ., 2006):

i) stimulation of insulin synthesis and/or secretion from pancreatic beta-cells

ii) regeneration/revitalization of damaged pancreatic beta cells

iii) improvement of insulin sensitivity (enhanced glucose uptake by fat and muscle cells)

iv) mimicking the action of insulin (acting like insulin)

iv) alteration of the activity of some enzymes that are involved in glucose metabolism

vi) slowing down the absorption of carbohydrates from the gut.

I.1.9.5. Investigation of some mechanism of action of antidiabetic plant extracts

Below is a brief description of some procedures used to investigate the in vivo effects of plant materials on insulin secretion, digestion and absorption of glucose, activation of the insulin receptor and the activity of some carbohydrate metabolizing enzymes.

· Effect on insulin secretion

In most published studies, investigation of the effect of medicinal plant extract on insulin secretion in vivo has involved the use of streptozotocin or alloxan induced animal models of diabetes (Eidi et al., 2006). Both alloxan and streptozotocin causes destruction of pancreatic beta cells resulting in reduced insulin secretion (Fröde and Medeiros, 2008). In streptozotocin and alloxan induced animal models of diabetes, insulin is markedly depleted but not absent (Fröde and Medeiros, 2008). For this reasons these animal models have been widely used to study the effect of antidiabetic remedies on insulin secretion in vivo.

· Intestinal digestion and absorption of carbohydrates

In order to investigate the effect of an antidiabetic plant extract on intestinal digestion and/or absorption of carbohydrates, study animals are usually divided into experimental and control groups. Experimental animals are given a plant extract under investigation while control animals are given a vehicle. An hour later, both groups of animals are given a fixed amount of glucose, sucrose or starch. Thereafter, blood glucose levels are measured at 0.5, 1, 1.5, 2 and 3 hrs after administration of the carbohydrate. Areas below the oral glucose tolerance curves of experimental groups are then calculated and compared with those of control groups (Hannan et al., 2007). Alternatively, a glucose tolerance test can be determined in the same group of animals before and after oral administration of the plant extract (Karato et al., 2006). A comparison of the glucose tolerance curve before and after oral administration of the plant extract will indicate whether or not the plant extract contribute to the delay in carbohydrate digestion and subsequent lowering of the blood glucose level glucose.

· Inhibition or activation of carbohydrate metabolizing enzymes

It has been establish that some antidiabetic remedies, for example, metformin exert its blood glucose effects by inhibiting endogenous glucose production by the liver through the process of gluconeogenesis and glycogenolysis (Bastaki, 2005). For this reason, as part of efforts to find out the possible mode of action of antidiabetic remedies, several researchers have investigated the effect of plant extracts on the activities of gluconeogenic enzymes: glucose 6-phosphatase, fructose 1,6-bisphosphatase; the glycogenolytic enzyme; glycogen phosphorylase and hepatic glucokinase. In order to investigate the effect of medicinal plant extract on key enzymes involved in glucose homeostasis in vivo, the study design used are similar to the one describe above for the study of the effect of plant extract on stimulation of insulin except that at the end of the feeding period blood and selected tissues are also collected for the measurement of the activity of selected enzymes in plasma or tissue homogenates in vitro.

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