A preliminary investigation of the possible hypoglycemic activity of Hibiscus rosa-sinensis

The hypoglycemic activity of an ethanol extract of Hibiscus rosa-sinensis was studied in glucose located rats. After a single dose of the extract, a slight but insignificant hypoglycemic effect was observed at 30 and 90 min. At 120 min it was mild but significant. After repeated administration of the extract (once a day for seven consecutive days) a statistically significant (P < 0.001) reduction in blood glucose levels was observed at 30, 90 and 120 min after glucose loading. The average hypoglycemic activity, after repeated administration of 250 mg kg-1 leaf extract was 81%, under similar conditions average activity of tolbutamide was 96%. At 250 mg.kg-1 the efficacy of the extract was found to be 84% of tolbutamide (100 mg.kg-1). Repeated treatment of animals either with tolbutamide a sulphonylurea or H. rosa-sinensis caused a 2-3-fold improvement in glucose tolerance as compared to those receiving only once. These data suggest that the leaf extract acts like tolbutamide and the mechanism of action may be a stimulation of pancreatic beta cells to produce more insulin or an increase of the glycogen deposition in liver. It appears that the active principle in the tested extract has the sulphonylurea skeleton in which-SO2-NH-CO-group and the substituents (S1 and S2) may be the possible active sites responsible for its hypoglycemic activity.