Insulin-releasing and insulin-like activity of the traditional anti-diabetic plant Coriandrum sativum (coriander)

Coriandrum sativum (coriander) has been documented as a traditional treatment of diabetes. In the present study, coriander incorporated into the diet (62·5 g/kg) and drinking water (2·5 g/l, prepared by 15 min decoction) reduced hyperglycaemia of streptozotocin-diabetic mice. An aqueous extract of coriander (1 mg/ml) increased 2-deoxyglucose transport (1·6-fold), glucose oxidation (1·4-fold) and incorporation of glucose into glycogen (1·7-fold) of isolated murine abdominal muscle comparable with 10−8 m-insulin. In acute 20 min tests, 0·25–10 mg/ml aqueous extract of coriander evoked a stepwise 1·3–5·7-fold stimulation of insulin secretion from a clonal B-cell line. This effect was abolished by 0·5 mm-diazoxide and prior exposure to extract did not alter subsequent stimulation of insulin secretion by 10 mm-l-alanine, thereby negating an effect due to detrimental cell damage. The effect of extract was potentiated by 16·7 mm-glucose and 10 mm-l-alanine but not by 1 mm-3-isobutyl-1-methylxanthine. Insulin secretion by hyperpolarized B-cells (16·7 mm-glucose, 25 mm-KCl) was further enhanced by the presence of extract. Activity of the extract was found to be heat stable, acetone soluble and unaltered by overnight exposure to acid (0·1 m-HCl) or dialysis to remove components with molecular mass < 2000 Da. Activity was reduced by overnight exposure to alkali (0·1 m-NaOH). Sequential extraction with solvents revealed insulin-releasing activity in hexane and water fractions indicating a possible cumulative effect of more than one extract constituent. These results demonstrate the presence of antihyperglycaemic, insulin-releasing and insulin-like activity in Coriandrum sativum.