ORIGINAL RESEARCH Inhibitory effect of Gymnema Montanum leaves on a-glucosidase activity and a-amylase activity and their relationship with polyphenolic content Kunga Mohan Ramkumar • Balsamy Thayumanavan • Thayumanavan Palvannan • Palanisamy Rajaguru Received: 18 February 2009 / Accepted: 25 August 2009 / Published online: 28 October 2009 Ó Birkha ¨user Boston 2009 Abstract The present study was attempted to investigate the effect of G. montanum leaf extract on inhibition of a-glucosidase and a-amylase activity. The ethanol extract of G. montanum (GLEt) at various concentrations (1–10 lg/ml) was tested for its inhibition pattern against a-glucosidase and a-amylase activity in vitro and compared with the commercially available a-glucosidase inhibitor, acarbose. The GLEt showed competitive inhibition against yeast a-glucosidase and non- competitive inhibition against salivary a-amylase in a concentration-dependent manner. Further, we investigated the effect of extract on levels of blood glucose and plasma insulin in neonatal streptozotocin-induced type 2 diabetic rats. Long-term administration (12 weeks) of the GLEt effectively reduced the blood glucose level and also increased the insulin level. In a preliminary phytochemical analysis, G. montanum leaves were rich in phenolic composition and found to be positively correlated with the inhibitory effect of a-glucosidase and a-amylase activity. These results suggest that the GLEt might exert its antidiabetic effect by suppressing carbohydrate absorption from the intestine and thereby reducing hyperglycemia. Keywords a-Glucosidase inhibitor  a-Amylase inhibitor  Gymnema montanum  Type 2 diabetes  nSTZ rats  Medicinal plants K. M. Ramkumar (&)  P. Rajaguru Department of Biotechnology, Anna University Tiruchirappalli, Tiruchirappalli 620 024, Tamil Nadu, India e-mail: km_ramkumar@rediffmail.com B. Thayumanavan Department of Biochemistry, Centre for Plant Molecular Biology, Tamilnadu Agricultural University, Coimbatore 641 003, India T. Palvannan Department of Biochemistry, Periyar University, Salem 636 011, India Med Chem Res (2010) 19:948–961 DOI 10.1007/s00044-009-9241-5 MEDICINAL CHEMISTR Y RESEARCH