Learning Outcomes
After completing this practical class students should be able to:
• Measure the concentration of glucose in the blood of a volunteer
• Explain the actions of insulin and glucagon on blood sugar levels
• Explain the regulation of plasma glucose by insulin and glucagon after a meal
• Describe the effect of dietary protein and stress on plasma glucose regulation
Introduction
Blood glucose levels are influenced by a number of hormones, the most important of which are insulin and glucagon. After ingesting a meal, these hormones are responsible for distributing and storing the glucose appearing in the blood.
This practical will examine the time course of plasma glucose levels following an oral dose of glucose. The effect of a more normal “diet” (ie. One containing fat, protein and carbohydrate) will also be examined. Finally the effect of stress (in the form of exercise), which also affects hormone levels, will also be investigated. While observing the changes in blood glucose, the hormonal changes occurring after a meal should be considered.
THERE IS SOME PRELIMINARY PREPARATION REQUIRED FOR THIS LABORATORY SESSION. MAKE SURE YOU ARE FAMILIAR WITH WHAT IS REQUIRED BY READING THE PROTOCOL THE DAY BEFORE ATTENDING THE LAB SESSION.
Method
Preparation: Fasting 8 to 10 hours prior to lab session
Volunteers should fast for 8 to 10 hours prior to the test only consuming clear water until the test is completed. (Morning lab session: fast from midnight; Afternoon session: fast from 6 am).
Exclusions: If there is a reason why you cannot participate as a subject in this practical (for example: diabetic, hypoglycaemic, prone to fainting) you can still participate by undertaking one of the experimenter roles.
On arrival at lab session, volunteers will be divided into 3 test categories:
Group A Standard OGTT
Group B Standard OGTT + food
Group C Standard OGTT + exercise
On day of test: Please arrive early for your lab session as you will need the full 2 hours to complete the OGTT.
1. Test Heart Rate and record in Table 1.
2. Wash hands with warm soapy water and dry.
3. Obtain a droplet of blood from your index finger (or other suitable, clean & dry part of your body e.g. forearm) using a lancet (ALWAYSuse a separate lancet per person). Record the blood glucose level. This is your fasting plasma glucose (FPG) reading.
4. All groups (A B and C): immediately drink the sugary drink provided within 5 minutes (this will deliver a 50 g glucose ‘load’).
5. Test group B will also consume a standard ‘meal’ (delivering protein, fat and carbohydrate) during the same 5 minute period
6. Test group C will perform light to moderate exercise (discuss with demonstrator) to raise their heart rate during the testing period.
7. Every 30 mins over the 2 hour recording period –
i. Determine heart rate
ii. Obtain a blood droplet and determine glucose concentration
iii. Record values in table provided
Results
1. Add your individual data to the appropriate columns below.
Table 1: Individual Glucose Levels & Heart Rates
Time (min) Test Condition
Group A Group B Group C
Standard OGTT Std OGTT + protein & fat Std OGTT + exercise
Glucose HR Glucose HR Glucose HR
0 (FPG)
30
60
90
120
2. Also add your individual data to the spreadsheets used to collect data for the whole class. These spreadsheets will be put on iLearn at the end of the session. They can then be downloaded for you to analyse the complete data set.
3. Plot your ‘individual’ blood glucose concentration and heart rate on the graph paper provided (Figures 1 & 2 respectively).
4. For the class data: Calculate the mean values for each time point and condition and then plot these mean values on the graph paper provided (Figure 3). Calculate and plot the means for all three sets of data (OGTT, OGTT + food, OGTT + exercise) on the same graph and then the data can be compared. Do the same for heart rate and create a graph of the mean values with sem.
5. Use statistical analysis to determine whether there is a significant difference between the peak glucose concentration for each condition (Group A, Group B and Group C)
The ftollowing questions are provided to help YOu write a discussion of your results. The
ques ions should not be written in your report, but provide direction for what to include. After
reading the report the reader should know the answers to all these questions.
0 Explain the purpose of the OGTT and what values for plasma glucose might be
expected at the 2 hour time point.
Why is it necessary to measure the glucose level after 2 hours and not after only 30
minutes in the OGTT?
What are the main hormones regulating blood glucose levels and what changes
would you expect after a glucose load?
What effect did the presence of protein/fat have on the plasma glucose concentration
after 30 mins? After 1 hour? After 2 hrs?
How and why would you expect the presence of fats/proteins in a meal to affect
blood glucose levels?
What effect did stress have on glucose concentrations after 30 mins? After 1 hr?
After 2 hours? What hormone(s) would you expect to be involved in this response?
How and why would you expect exercise to influence blood glucose after a glucose
meal?
Are the effects of stress or food on blood glucose levels statistically different from the
results of the standard OGTT? What statistical test did you use to analyse the results
and why?
0 What are some of the problems with diagnosing diabetes based on a single blood
glucose concentration? How do clinical fasting plasma glucose (FPG) and OGTT
tests control for these problems?