Stimulation of insulin secretion by extracts of piper tuberculatum - abstract

ABSTRACT

Piper tuberculatum, locally known as candle-bush, is widely used in folk medicine in Trinidad and Tobago in the control of diabetes mellitus. It is commonly administered as a tea prepared from the leaves of the plant. This study was undertaken to investigate the hypoglycaemic activity (if any) of the plant, to identify and partially purify the active component and to obtain some information on the mechanism(s) of action. A methanol extract of leaves of the plant was screened for hypoglycaemic activity. The chloroform phase obtained from a chloroform form/H[2]O partition of the extract contained the active component which was further partially purified by column and thin-layer chromatography. Based on the chromatographic behaviour and HNMR spectroscopy, the active component was indentified as an amide alkaloid, most likely piplartine or a closely related derivative. The hypoglycaemic activity of the component, as tested on streptozotocin-diabetic rats, was found to be similar to that of an authentic sample of piplartine. The partially purified active component produced an increase in phospholipase C activity of the plasma membrane of pancreatic islet cells and induced insulin secretion in diabetic rats. The exact mechanism of the stimulation of insulin release requires further investigation but may be similar to that of sulphonylureas (AU)