Introduction

Glucose tolerance test in mice are a way to measure the development of Type 2 diabetes in mice exposed to high fat diet. While the procedure is not difficult per se, it takes roughly 2.5 hours to do. For beginners, I would strongly advise people to do it maximum 5 mice by 5 mice before increasing the number of animals.

Protocol

Material

• Glucometer
• Alcohol wipes
• Glucose strips (Count roughly 40-45 for 5 mice just in case).
• Becker with warm water
• A long hypodermic needle
• A mouse holder
• Insulin syringe
• Scale
• Glycometer controls if you open a new box of strips.
• A timer (Or your phone).

On the day before the test

• Weight all of your mice.
• Prepare a 0.2 g/mL solution of glucose. For that, just put 2g of powdered glucose in 10 mL of saline solution and mix it until it dissolves.
• Before light extinction, remove all the food from the mice. You can keep them group housed.
• Verify the quality of your glucose strips with a control test

These two solutions are present with the accucheck glucometer and are used to control the quality of a new box of strips. JUst inset one strip in the glycometer, turn it on (Press OK) and put ONE DROP of the Control 1 solution on the edge of the strip (Yellow part)

the Accu-check meter will detect if it's the test solution 1 or 2 and will tell you if it's in the normal range or not. If it's in the normal range, press ok and repeat the test with the test solution 2.

On the day of the test

• Take your mice cage in a calm room where you will be undisturbed.
• Take an additional cage to put your mice in on "standby".
• Take your first mouse, put it in the mouse-holder :

It"s a bit tricky to a mouse inside, especially when they are overweight. You need to put the mouse at the open end entry, grab it's tail, and gently but progressively pull the mouse tail accross the tube with the slot until the mouse reach the bottom of the tube and the tail is fully accessible. Then restrain the mice with the plug so the animal stay still.

• Desinfect the tail with an alcohol strip
• Plunge the end of the tail (last 3rd) in the warm water becker
• With the needle, poke the dorsal or lateral vein :

• Massage the part of the tail around the puncture to "squeeze" a drop of blood.
• Put a strip in the accucheck glucometer and turn it on, it will say "APPLY DROP".
• Apply a drop on the yellow part of the strip, the drop needs to be consequent enough or else you won't have a reading.
• Read the measure at T0.
• Inject the mouse with 2g/kg of glucose in i.p
• Put it in the stand-by cage.
• Repeat glucose prelevement at 15, 30, 60, 90, 120 minutes after the injection.
• At the end of the procedure, give to the mice ad libitum food.

Expected results

A glucose tolerance test done on 5 HFD fed (Red) and 5 chow fed (Black) mice should look like this :

Potential issues & precautions

• ALWAYS wear gloves. Change them regularely to not contaminate strips.
• The first puncture is always the hardest, after that it's just finding out where you got the first puncture and try to poke it slightly to squeeze out blood again.
• If the reading says "LO" it means the glucose concentration is less than 15 mg/dl. It's highly unlikely that it would occcur. Test again in a new strip, if it's the same reading, test again with a new box of strips. If it's the same results again, check your mice for a hypoglycemic choc.
• If the reading says "HI" it means that the glucose concentration reached above 600 mg/dL and cannot be measured properly. It especially happens in obese mice. Test again with a new strips, if it's the same results, then count the reading as 600 mg/dl.