Oral Glucose Tolerance Test (OGTT): Measuring Glucose Metabolism in Mice

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

1. Oral Glucose Tolerance Test (OGTT)

1. Glucose solution preparation: Before conducting the experiment, prepare the glucose solution by dissolving 3.75 g glucose in 15 mL distilled H₂O.
2. Set up a timetable to record the readings during the experimental procedure (Table 1).
   NOTE: It is important to set up a timetable with proper intervals between each blood examination to allow accurate recording during the experiment.
3. Weigh each mouse after fasting and calculate the appropriate amount of glucose to be injected. For example, if the mouse weighs 30 g, the amount of glucose solution to be administered should be 300 µL.
4. Prepare the following instruments at the workbench:
   1. Glucometer (Press the Start button to check the battery status, make sure it is functioning before the test.)
   2. Glucose chip
   3. Insulin syringe (0.3 mL Insulin syringe)
   4. Razor blades
   5. Timer
5. Once the bench is set up, measure and record the blood glucose level as follows: Put a clean and new glucose chip into the glucometer and press the Start button to zero it.
6. Pick up the mouse by the back of the neck and stroke the tail a few times to ensure sufficient blood flow to the tail region.
7. Using a new razor blade, cut off a small piece of the tail and squeeze out one small drop of blood (about 10-20 µL) into the glucose chip. The blood should fill the chip to allow accurate measurement. The glucometer will display the glucose level immediately. If the machine shows "error", repeat the procedure with a new glucose chip.
   NOTE: The glucose chip requires only one drop of blood. When the blood sample needs to be collected more than once, simply apply pressure by running your fingers along the mouse's tail several times while holding the end of the tail directly on top of the chip to collect blood. It is not necessary to cut the tail end each time while collecting blood samples.
8. Next, feed the mice glucose (0.25 g/mL) orally by using the intragastric gavage technique. The amount of glucose to be administered should be calculated by using the formula: 10X body weight (BW) µL glucose solution (for example, if the mouse weighs 30 g, the amount of glucose solution to be administered will be 300 µL). Start the timer immediately after administering oral glucose.
9. Repeat the glucose measurement procedure at 15, 30, 60, 90, and 120 min.
10. After all the glucose level readings have been recorded, discard the razor blades and glucose chips in a biohazard container. Put the food back into the mice cages and return them to the animal room.

Table 1. Timetable for Oral Glucose Tolerance Test (OGTT) recording