Influence of oral glucose load upon blood glucose level in relation to the time of day.

Blood glucose levels were estimated at different times of day in fasted rats and after 30, 60,90 and 120 min, since oral glucose load. Circadian variations in basal glucose levels and in the levels after glucose load were observed with the highest values noted between 11 a.m. and 7 p.m., and the lowest ones about midnight. These variations were most prominent when the measurements were performed 60 min after glucose load. Circadian variation in glucose tolerance was also revealed with the best tolerance at about midnight while the worst one was noted at noon and in the afternoon.