Glucose entrainment of high-frequency plasma insulin oscillations in control and type 2 diabetic subjects.
Regular high-frequency oscillations of insulin secretion are characteristic of normal beta-cell function. These oscillations are easily entrainable to an exogenous rhythm by small changes in glucose concentration in vitro. We tested whether high-frequency insulin oscillations in vivo would also be entrainable by glucose and whether a lack of entrainment would characterize the diabetic beta-cell. We tested 13 control subjects and 11 patients with type 2 diabetes. Subjects underwent serial blood sampling at 1-min intervals for 60-120 min in the basal state or with small (15 mg/kg) boluses of glucose injected intravenously at exact 29-min intervals. Time series analysis was carried out using spectral analysis. Oscillations of basal plasma glucose concentrations were observed in both control and type 2 diabetic subjects, with a mean period of 11.3 +/- 3.1 and 11.6 +/- 2.0 min, respectively. These oscillations were entrained to mean periods of 15.0 +/- 0.6 and 14.2 +/- 0.9 min, respectively, by exogenous glucose. Regular high-frequency insulin oscillations were observed in control subjects; the mean period of basal plasma insulin oscillations was 10.7 +/- 1.2 min and was entrained to exogenously injected glucose, with a period of 15.2 +/- 0.1 min. In contrast, in the type 2 diabetic subjects, spontaneous insulin oscillations were unchanged by the glucose rhythm; the mean periods were 10.0 +/- 1.0 min during the basal period, and 10.1 +/- 0.0 min during glucose injections. These results demonstrate that spontaneous high-frequency insulin oscillations can be successfully entrained by glucose in control subjects. However, these oscillations in type 2 diabetic subjects are not similarly entrained. We conclude that loss of entrainment of spontaneous high-frequency insulin oscillations in type 2 diabetes is a highly sensitive manifestation of beta-cell secretory dysfunction.
Mao
C S
CS
Department of Medicine, Harbor-UCLA Medical Center, Torrance, California 90509-2910, USA.
Berman
N
N
Roberts
K
K
Ipp
E
E
D000328:Adult; D000368:Aged; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007275:Injections, Intravenous; D007328:Insulin / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009991:Oscillometry; D012016:Reference Values
D007328:Insulin; D005947:Glucose