The aim of the present work is to study and compare antidiabetic activity of extracts from Catharentus roseus, Persea americana, and Eucalyptus globulus as well as their mechanism of action. The aqueous and methanolic plant extracts were respectively prepared by decoction and maceration. The phytochemical screening was done by standard methods. The extracts were subsequently tested in vivo on Wistar albino rats (Rattus norvegicus) with temporary hyperglycemia. The methanolic extract of P. americana leaves showing the best activity was selected for the antidiabetic test at doses 37.5, 75 and 150 mg/kg. For that purpose, permanent diabetes mellitus was induced in rats fasted overnight by intraperitoneal injection of alloxan (150 mg/kg). Hematological and biochemical parameters were evaluated from the cardiac puncture’s blood. The antidiabetic mechanism of action of the 6 extracts was performed by evaluating their inhibitory activity on alpha glucosidase, beta glucosidase and glucoamylase. Phytochemical analysis of aqueous and methanolic extracts revealed that all extracts contain phenols, anthraquinones and tannins. On the other hand, no extract contains sterols. All extracts showed hypoglycemic activities. The antidiabetic tests showed that the methanolic extract of P. americana caused a decrease in blood sugar level in all the treated rats with the dose of 150 mg / kg of body weight being the most effective, without any adverse side effect in the animals. All the tested extracts showed an inhibitory activity against alpha glucosidase and glucoamylase enzymes and have no inhibitory activity on beta glucosidase. The results of the present study demonstrate the antidiabetic properties of the tested plants through inhibitory effect on alpha glucosidase and glucoamylase enzymes with P. americana being the most active.

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