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Induction of insulin secretion by an aqueous extract of Tabernanhte iboga Baill. (Apocynaceae) in rat pancreatic islets of Langerhans.

par Souza, Alain;Mbatchi, Bertrand;Herchuelz, André
Référence Journal of ethnopharmacology
Publication Publié, 2010-11

Article révisé par les pairs

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Résumé :

The effect of an aqueous extract of Tabernanthe iboga (TBEt) was studied in the rat islets insulin secretion based on its use in traditional medicine for the treatment of diabetes. The extract (10(-3)μg/ml-100μg/ml) did not exert a significant increase of insulin secretion (p>0.05) in the presence of 2.8mM of glucose (a none stimulatory concentration). Whereas, in the presence of 11.1mM of glucose (stimulatory concentration), TBEt augmented glucose-stimulated insulin secretion in a dose-dependent manner. Interestingly, the secretory effect of the extract was glucose-dependent (5.6-16.7mM). Furthermore, the insulinotropic effect of TBEt (1μg/ml) was significantly potentiated (p<0.001) in K(+)-depolarised media as well as in the presence of 2.8mM and 16.8mM of glucose concentrations. In contrast, in the same conditions, TBEt failed to stimulate the high K(+) medium-induced insulin release. The extract significantly amplified (p<0.001 and p<0.05) the insulin secretion induced by either IBMX or tolbutamide. Diazoxide, cobalt or calcium removal inhibited the insulinotropic effect of the extract. TBEt increased glucose-induced (45)Ca(2+) uptake in rat islets. Overall, our findings suggest that Tabernanthe iboga contains water soluble insulinotropic compounds. The insulin secretion of TBEt's active principles might involve the closure of K(+)-ATP and the intensification of calcium influx through voltage-sensitive Ca(2+) channels.