Insulin-like effect of pinitol

1. D-pinitol (3-O-methyl-chiroinositol), an active principle of the traditional antidiabetic plant Bougainvillea spectabilis, is claimed to exert insulin-like effects. This study investigates the effect of D-pinitol on glucose homeostasis in animal models of diabetes, and on glucose transport by cultured muscle cells. 

2. Plasma glucose concentrations were measured in normal, obese-diabetic (ob/ob) and streptozotocin (STZ)-diabetic mice after oral (p.o.) and intraperitoneal (i.p.) administration of D-pinitol. Glucose transport was measured in L6 rat muscle cells by 2-deoxyglucose (2DG) uptake. 

3. In STZ-diabetic mice, 100 mg kg ^-1 p.o. D-pinitol acutely decreased the hyperglycaemia (by 22% at 6 h). A similar decrease in plasma glucose (by 21%) was observed after 100 mg kg(-l) i.p. D-pinitol. Insulin concentrations and the rate of insulin-induced (1 unit kg ^-1 actrapid i.p.) glucose disappearance were not altered by 100 mg kg ^-1 p.o. D-pinitol. Chronic administration of D-pinitol (100 mg kg ^-1 i.p. twice daily for 11 days) to STZ-diabetic mice maintained a reduction in plasma glucose concentrations from about 14 to 10 mmol 1 ^-1. 

4. In normal non-diabetic and severely insulin resistant ob/ob mice, 100 mg kg ^-1 p.o. D-pinitol did not significantly affect plasma glucose or insulin during acute studies. 

5. Incubation of L6 muscle cells with D-pinitol (10 ^-3 M) increased basal 2DG uptake by 41% after 10 min and by 34% after 4 h. The effect of D-pinitol was inhibited by the phosphatidylinositol 3-kinase inhibitor LY294002. D-pinitol did not increase insulin-stimulated 2DG uptake by L6 cells. 

6. The data support the view that D-pinitol can exert an insulin-like effect to improve glycaemic control in hypoinsulinaemic STZ-diabetic mice. D-pinitol may act via a post-receptor pathway of insulin action affecting glucose uptake.