Effect of Scoparia dulcis extract on insulin receptors in streptozotocin induced diabetic rats: studies on insulin binding to erythrocytes.

We investigated the insulin-receptor-binding effect of Scoparia dulcis plant extract in streptozotocin (STZ)-induced male Wistar rats, using circulating erythrocytes (ER) as a model system. An aqueous extract of S dulcis plant (SPEt) (200 mg/kg body weight) was administered orally. We measured blood levels of glucose and plasma insulin and the binding of insulin to cell-membrane ER receptors. Glibenclamide was used as standard reference drug. The mean specific binding of insulin to ER was significantly lower in diabetic control rats (DC) (55.0 +/- 2.8%) than in SPEt-treated (70.0 +/- 3.5%)- and glibenclamide-treated (65.0 +/- 3.3%) diabetic rats, resulting in a significant decrease in plasma insulin. Scatchard plot analysis demonstrated that the decrease in insulin binding was accounted for by a lower number of insulin receptor sites per cell in DC rats when compared with SPEt- and glibenclamide-treated rats. High-affinity (Kd1), low-affinity (Kd2), and kinetic analysis revealed an increase in the average receptor affinity in ER from SPEt and glibenclamide treated diabetic rats having 2.5 +/- 0.15 x 10(10) M(-1) (Kd1); 17.0 +/- 1.0 x 10(-8) M(-1) (Kd2), and 2.0 +/- 0.1 x 10(-10) M(-1) (Kd1); 12.3 +/- 0.9 x 10(-8) M(-1) (Kd2) compared with 1.0 +/- 0.08 x 10(-10) M(-1) (Kd1); 2.7 +/- 0.25 x 10(-8) M(-1) (Kd2) in DC rats. The results suggest an acute alteration in the number of insulin receptors on ER membranes in STZ-induced diabetic rats. Treatment with SPEt and glibenclamide significantly improved specific insulin binding, with receptor number and affinity binding (p < 0.001) reaching almost normal non-diabetic levels. The data presented here show that SPEt and glibenclamide increase total ER membrane insulin binding sites with a concomitant significant increase in plasma insulin.