Objective: To study the characteristics of insulin ultradian pulses of individuals with normal glucose tolerance, overweight, and impaired glucose tolerance (IGT).
Methods: Blood samples were taken every 15 minutes from 10 individuals with normal glucose tolerance, 6 individuals with overweight and 3 individuals with IGT for 24 hours. Blood glucose, insulin, and C-peptide of every time point were measured. Standard diet was used in the study. The 24 h-ISR profile was submitted to time series analysis.
Results: (1) As given standard diet, 2 to 4 pulses occurred after each meal, 3 to 4 pulses occurred during the night, and 12 to 15 pulses occurred in the whole 24-hour period. The first insulin pulse always occurs 30 to 60 minutes after meal. The maximum amplitude of pulse occurred 45 to 90 minutes after meal. These characteristics were not significantly different among the 3 groups. (2) The average amplitude of 24-hour insulin secretion rate (ISR) of the normal group was 357 pmol/min +/- 11 pmol/min, significantly lower than those of the overweight and IGT groups (820 pmol/min +/- 37 pmol/min and 666 pmol/min +/- 53 pmol/min respectively, both P < 0.05). (3) The average periodicity of insulin ultradian pulse were 75 min and 75 - 90 min in the control group and overweight group respectively. The periodicity of insulin ultradian pulse in the IGT group was undefined. (4) The cross-correlation function were 0.72 +/- 0.11, 0.80 +/- 0.11 and 0.51 +/- 0.11 respectively in the normal, overweight, and IGT groups.
Conclusion: (1) As given standard diet, the occurring numbers and time of insulin ultradian oscillations are not statistically significantly different among the normal, overweight, and IGT groups. (2) The insulin secretion amplitude is increased in the overweight and IGT groups. (3) The rhythm and concomitance coefficient of the ISR and glucose are low in the individuals with IGT.