Circadian variation in glucose tolerance and associated changes in plasma insulin and somatostatin levels in normal volunteers.

The day-time variations of blood sugar and associated changes in plasma insulin and somatostatin levels in response to glucose-glucagon load were investigated in eight healthy volunteers. The glucose-glucagon test was performed in the same subjects at 9.00 a.m., at 5.00 p.m. and at midnight after 10 hrs of fasting. The blood sugar values were higher in the midnight while the corresponding plasma insulin levels were significantly lower. Plasma somatostatin levels did not differ at the different times of the day. These results suggest that the circadian variations of the glucose tolerance are correlated to a simultaneous circadian rhythmicity in the insulin response in the sense of a decreased insulin release later in the day. Somatostatin does not seem involved in the circadian variation of beta cell responsiveness observed in healthy volunteers.