Aqueous extract of Momordica dioica stimulates insulin release from isolated rat islets

Momordica dioica (Cucurbitaceae) has been used for management of diabetes by ethnic groups in Bundelkhand region of central India. Increase in serum insulin in diabetic Wistar rats by aqueous extract of fresh unripe fruits M. dioica has been reported earlier by our group (1). To confirm insulin secretagogues potential of M. dioica, aqueous extract (AE) and methanol soluble fraction (MSF) and methanol insoluble fractions (MIF) of AE were subjected to In Vitro insulin release assay from isolated pancreatic islets of normoglycemic Wistar rats. ATP dependant potassium channel opener drug nicorandil was employed to investigate possible mechanism of insulin release. Isolated pancreatic islets of rat in HBBS containing 1% BSA were incubated with glucose (3.3/16.7mM) and 1mg AE, MSF, MIF or 1mg of nicorandil. Release of insulin in external media was measured by ELISA. Glucose at 16.7 mM level stimulated insulin release as compared to 3.3mM, proving the sensitivity of the assay. AE and MSF of M. dioica significantly (p<0.01) increased insulin release were as MIF was not able to enhance insulin release. The results indicated that the active principle was present in methanol soluble fraction of aqueous extract. Trypan blue staining and LDH release assay from isolated islets indicated that the extracts were non cytotoxic at tested concentration and the insulin release was not merely by alteration of membrane permeability by M. dioica extracts. Nicorandil did not inhibit M. dioica mediated stimulation of insulin release, indicating that mechanism of insulin release by M. dioica was independent of k-ATP and Ca voltage gated channels of pancreatic β-cells.