Diurnal variation in blood sugar and serum insulin in response to glucose and/or glucagon in healthy subjects.
The role of insulin secretion in the diurnal variation of glucose tolerance has been investigated. In ten healthy subjects, at 08.00 and at 18.00 after 10 hrs of fasting, a combination test of glucose and glucagon was performed. 1 mg glucagon was injected intravenously 40 min after the intravenous infusion of glucose (0.5 g/kg b.w.). Samples for blood sugar (BS) and serum immunoreactive insulin (IRI) were taken before and 2-5 min following the glucose and glucagon loads, and thereafter at 10 min intervals up to 85 min. In the afternoon test, the mean blood sugar values were higher, the differences in the 20-85 min values being statistically significant: the IRI values were statistically lower after glucose, while after glucagon, the increase of serum IRI was apparently similar in both morning and afternoon tests. However, the insulin/glucose ratio (I/G) was significantly lower at 18.00 at 55-85 men. Corresponding results were obtained in six additional healthy subjects when only glucagon (1 mg i.v.) was injected. In this case also, the mean insulin levels were lower in the afternoon after 5 min, while the BS values during the maximal insulin release (2-30 min) were comparable in both the morning and afternoon tests. In the 40-60 min interval, the BS levels were significantly higher in the afternoon. The existence of a diurnal variation in the blood sugar after intravenous glucose load, as well as after glucagon, seems to be correlated to a simultaneous diurnal variation in the insulin response, suggesting decreased pancreatic beta-cell activity in the afternoon.