Influence of Exercise on Post-Exercise Glucose Disposal

 Background :

Researchers use either the euglycemic hyperinsulinemic clamp or the oral glucose tolerance test to assess the body's ability to dispose of blood glucose.  Of the two methods, the OGTT is the easiest to perform as it only requires the ingestion of 75 gm of carbohydrate, followed by repeated blood draws for two hours for the latter assay of blood (serum) glucose.

Purpose:

The purpose of this lab is to compare the blood glucose response to 75 g of ingested glucose in one individual after two conditions.  One trial will require the ingestion of the CHO after cycle ergometry (lower body only) exercise, whereas the second trial will require 45 min of prior supine rest.  The blood glucose response will be compared by determining the area under the 1.5 hour blood glucose curve for each trial.  A secondary purpose is to compare two different assay methods for glucose.

Experimental Procedure:

1. A venous catheter will be inserted, with connections to a 3-way stop cock and a syringe of saline.

2. After a resting blood sample is obtained (3 ml), the specific 45 min pre-ingestion session will be performed.

3. For the exercise trial, determine steady state VO2 at minutes 5, 20, and 40.

4. Immediately after exercise, 75 gm of CHO will be ingested (75 gm glucose in 600 mL flavored water=12.5% solution).

5. At minutes 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 110 and 120, 2 ml samples of blood will be drawn.

6. All blood samples will be dispensed into tubes containing sodium fluoride, left to clot at 4 ºC, and then centrifuged and the serum stored in vials at 4 ºC for latter assay of glucose.

7. For the rest trial, everything is the same as above, but the 45 min exercise session is replaced with 45 min of supine rest.

 Glucose will be assayed by an enzymatic assay as well as a colorimetric assay.  These assays will be posted to the assay page later in the week.

 Data Analyses :

*  Graph the changes in blood glucose for each trial.

*  Determine the area under the curve for the post-exercise data of each trial using Prism.

*  Explain the blood glucose differences between trials, and predict how insulin would be different for each trial.

*  Use the term insulin sensitivity and glucose disposal to describe the differences in the blood glucose response between the subjects.

*  Why does exercise increase insulin sensitivity and glucose disposal?

*  How does this response aid the diabetic and prevent diabetes?

 References

 Beard J., R. Bergman, W. Ward and D. Porte. The insulin sensitivity index in nondiabetic man: corerlation between clamp-derived and IVGTT-derived values. Diabetes. 35:362-369, 1986.

 Seals D., J. Hagberg, W. Allen, B. Hurley, G. Dalsky, A. Ehsani and J. Holloszy. Glucose tolerance in young and older athletes and sedentary men. J. Appl. Physiol. 56(6):1521-1525, 1984.

Young J., J. Enslin and B. Kuca. Exercise training and glucose tolerance in trained and non-trained subjects. J. Appl. Physiol. 67(1):39-43, 1989.