INCREASED DISORDERLINESS OF BASAL INSULIN RELEASE, ATTENUATED INSULINSECRETORY BURST MASS, AND REDUCED ULTRADIAN RHYTHMICITY OF INSULIN-SECRETION IN OLDER INDIVIDUALS

Insulin is secreted in a pulsatile fashion. Rapid pulses are considere d to be important for inhibiting hepatic glucose output, and ultradian pulses for stimulating peripheral glucose disposal. Aging is 0charact erized by a progressive impairment in carbohydrate tolerance. We under took the current studies to determine whether alterations in pulsatile insulin release accompany the age-related changes in carbohydrate met abolism. Healthy young (n = 8; body mass index, 21 +/- 1 kg/m(2); age, 24 +/- 1 yr) and old (n = 9; body mass index, 24 +/- 1 kg/m(2); age, 77 +/- 2 yr) volunteers underwent two studies. In the first study, ins ulin was sampled every 1 min for 150 min, and pulse analysis was condu cted using a recently validated multiparameter deconvolution technique . In the second study, insulin was sampled every 10 min for 600 min, a nd insulin release was evaluated by Cluster analysis. In the 150-min s tudies, insulin secretory burst mass (P < 0.05) and amplitude (P < 0.0 1) were reduced in the elderly. In addition, approximate entropy, a me asure of irregularity or disorderliness of insulin release, was increa se in the aged (P < 0.01). In the 600-min studies, interpulse interval was greater in the aged (P < 0.05), and burst number was less (P < 0. 05). We conclude that normal aging is characterized by more disorderly insulin release, a reduction in the amplitude and mass of rapid insul in pulses, and a decreased frequency of ultradian pulses. Whether thes e alterations in insulin pulsatility contribute directly to the age-re lated changes in carbohydrate metabolism Rill require further study.