α-Glucosidase Inhibitory Activity of Some Sri Lanka Plant Extracts, One of Which, Cassia auriculata, Exerts a Strong Antihyperglycemic Effect in Rats Comparable to the Therapeutic Drug Acarbose

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Abstract
Some Sri Lanka plant stuffs were examined regarding in vitro and in vivo α-glucosidase (AGH) inhibitory actions. According to the results, water extracts and methanol extracts of dried fruits of Nelli (Phylanthus embelica), methanol extracts of dried flowers of Ranawara (Cassiaauriculata), and water extracts of latex of Gammalu (Pterocarpus marsupium) were found to have a potential AGH inhibitory activity. In particular, Ranawara methanol extract showed the strongest AGH inhibitory activity in vitro preferably on maltase giving an IC50 value of 0.023 mg/mL and inhibited the maltase activity competitively. As a result of single oral administration of Ranawara (C.auriculata) methanol extract in Sprague−Dawley rats, a significant and potent lowering of blood glycemic response toward maltose ingestion was observed at 30 min after dosing of 5 mg/kg, thus, concurrently suppressed insulin activity. The ED50 of the extract (4.9 mg/kg) clearly indicated that the antihyperglycemic effect was as potent as that of therapeutic drug, acarbose (ED50 3.1 mg/kg). Keywords: α-Glucosidase; antidiabetic plants; diabetes mellitus control; Phylanthus embelica; Cassia auriculata; Pterocarpus marsupium