Recovery of oral glucose tolerance by wistar rats after treatment with Coreopsis tinctoria infusion

Infusions of Coreopsis tinctoria flowering tops have traditionally been used in Portugal to control hyperglycaemia but no pharmacological or toxicological studies have been reported until now. The chalcones marein and okanin were isolated from the aqueous extract, together with the 2S‐3′,4′,7,8‐tetrahydroxyflavanone. The content of marein in extracts was determined by HPLC‐UV and the radical scavenging capacity evaluated by the DPPH method (EC₅₀ = 21 µg/mL). Glucose intolerance was induced by a single intraperitoneal injection of streptozotocin in saline (40 mg/Kg). After three weeks of oral treatment with C. tinctoria extract (500 mg/Kg/day) the animals were no longer glucose‐intolerant (p > 0.05). Additionally, this oral treatment caused no hepatotoxicity in the rats, as determined by blood alanine and aspartate transaminases. A single administration of extract had no effect on oral glucose tolerance in normal Wistar rats. The extract also had no effect on insulin secretion by MIN6 cells. In conclusion, C. tinctoria infusion is able to abolish the streptozotocin‐induced glucose‐intolerance in rats after three weeks of oral treatment by a mechanism other than induction of insulin secretion. The recovery of β‐pancreatic function mediated by an antioxidant mechanism is a possibility that deserves further investigation. Copyright © 2009 John Wiley & Sons, Ltd.