#R4948

Glucose Tolerance Test for Endocrine Labs

Well described laboratory that focuses on regulation of blood glucose levels. Clear instructions for students and detailed instructor guidelines. Worksheet is well designed. Sharing of pooled data with class after completion of the laboratory exercise will be very important.
—Thomas Schmidt, UIowa

The information on the effects of caffeine on glucose levels is not the only potential outcome as studies on both normal and diabetic individuals have shown that caffeine increases plasma levels of insulin. However, this prolonged increase in insulin levels did not result in a lower level of blood glucose. In fact, blood glucose was significantly greater following ingestion of caffeine. The data suggest that caffeine ingestion results in insulin resistance. This may be due in part to the release of epinephrine (also known as adrenaline) which interferes with insulins actions. ß-adrenergic receptor binding triggers glucagon secretion in the pancreas, increased plasma cortisol levels due to adrenocorticotropic hormone (ACTH) secretion by the pituitary gland, and increased lipolysis by adipose tissue. Together, these effects lead to increased blood glucose and fatty acids, providing substrates for energy production within cells throughout the body. The effect of caffeine in an individual would depend on the amount and regularity of their prior consumption.

Participants chosen for the glucose tolerance test should be fasting, otherwise it is not truly an assessment of their response to a known glucose load. In addition to potentially impacting the absorption of glucose from the digestive tract, having eaten a meal prior to the test may result in the baseline value for blood glucose being elevated and the additional carbohydrate intake may prolong the elevation of blood glucose causing levels to remain elevated during the 90 minute period of the test. Students should be made aware that if they have eaten an abnormal test is not necessarily indicative of diabetes.
—Greg Brower, Texas Tech University Health Sciences Center