After 5 hours fast (15 hours for rats), animals are given 50% glucose via oral gavage or IP injection at 1~2.0g/kg. Blood samples are collected prior to and after the gavage/injection at time 0, 15, 30, 60, and 120 minutes via tail vein bleeding.  Blood levels of glucose are measured using a glucometer (Acucheck, Roche) and plasma levels of insulin are determined using Millipore rat/mouse insulin ELISA kit. Animals are restrained repeatedly for less than a minute each time while blood samples are collected.