Context: Insulin is secreted in a pulsatile fashion with measurable orderliness (low entropy). Normal aging and diabetes in middle-aged patients is characterized by alterations in pulsatile insulin release.
Objectives: We undertook the current studies to determine whether disruptions in pulsatile insulin release also accompany diabetes in the elderly.
Design: Two studies were performed. In the first study, insulin values were sampled every minute for 1 h under fasting conditions. In the second study, subjects underwent a 2-h hyperglycemic glucose clamp (glucose 5.4 mm above basal). From 60-120 min, insulin was sampled every 1 min. Secretory pulse analysis was conducted using a multiparameter deconvolution technique.
Setting: The study was conducted in a general clinical research center and during outpatient visits.
Patients: Volunteers were healthy young [n = 10; body mass index (BMI), 23 +/- 1 kg/m2; age, 23 +/- 1 yr] and elderly (n = 10; BMI, 24 +/- 1 kg/m2; age, 78 +/- 2 yr) volunteers and elderly patients with diabetes (n = 8; BMI, 28 +/- 1 kg/m2; age, 73 +/- 2 yr).
Intervention: Five of the older patients with type 2 diabetes (BMI, 29 +/- 1 kg/m2; age, 72 +/- 2 yr) were treated with continuous sc glucagon-like peptide-1 (GLP-1) (7-36) amide infusion for 6 wk, and a second 2-h hyperglycemic clamp was performed.
Main outcome measures: Insulin burst mass, pulsatile insulin secretion, and entropy were measured.
Results: Under fasting conditions, elderly patients with diabetes had a reduction in insulin burst mass (P < 0.05) that was similar to normal elderly. During hyperglycemia, elderly patients with diabetes had an even greater impairment in insulin burst mass (P < 0.05) and basal (P < 0.05) and pulsatile insulin secretion (P < 0.05) than normal elderly. Approximate entropy, a measure of irregularity of insulin release, was increased to a greater extent in older diabetes patients than normal elderly, signifying loss of orderliness of insulin secretion (P < 0.05). In response to treatment with GLP-1, insulin burst mass (P < 0.05) and pulsatile insulin secretion (P < 0.05) improved significantly in elderly patients with diabetes.
Conclusions: We conclude that alterations in pulsatile insulin release can be improved in elderly patients with diabetes by the administration of sc GLP-1.