Second international School On Mind, Brain And Education

2007, May 22-26

Basic and Applied Topics
in Biological Rhythms and Learning

Directors: Antonio M. Battro and Kurt W. Fischer
Program officer: María Lourdes Majdalani

Abstract: M. Teresa Mondéjar

Oral glucose tolerance test and sleep wake state to acquaint chronobiology students with the importance of timing as a diagnostic tool
It is well documented that data obtained from the oral glucose tolerance test (OGTT) vary depending on the time of day. Our aim was to use these circadian variations in the response to OGTT to initiate Chronobiology students in the analysis of circadian rhythms. Since 2002, and as part of the laboratory sessions, a total of 111 healthy students between 19-25 years received 50 g of glucose (Glucomedics®) at different times (at 9h, 12h, 15h, 18h, 21h, 0h, 3h and 6h). In order to reduce disturbances, each student were submitted only twice to the OGTT with a time shift of 12 hours. In addition ten subjects were volunteered to lay in bed, either sleeping or awake registering the glucose plasma levels every 6 hours, to analyse the influence of the sleep/wake state on this test. After the oral glucose load, glycaemia was measured by glucometer (Gmeter, Menarini®) every 30 minutes for 150 minutes. To avoid individual differences, increments over the baseline glycaemia were compared.
The results showed that plasma glucose reached the highest level at night (with a peaked at 0h) and remained high longer than during daytime. At 9h glucose increase was fastest (Tmax=38 minutes) than at the other hours tested. Furthermore, in the morning hours (9-12h) normoglycaemia was recovered quickly (within 120 minutes), hypoglycaemic bursts being eventually observed. At 6h plasma glucose remained elevated after 150 minutes in sleeping subjects, while approached normoglycaemia in awaken subjects. In conclusion, not only our results highlighted the impact of OGTT timing and the sleep/wake state, since glycaemia regulation differs remarkably in the morning versus evening-night, but in addition our students experienced by themselves the importance of an adequate timing for diagnostic porpoises.