Insulin secretion, clearance dynamics, and their relationship to peripheral plasma insulin and glucose levels were monitored during three 12-h periods of overnight rest, intake of three meals, and continuous enteral feeding of mixed nutrients. The low-frequency ultradian and the high-frequency insulin secretion pulsatility characteristics during the steady-states of overnight rest and continuous enteral feeding were also examined. In abdominally obese subjects, the insulin secretion rate was consistently higher than normal by 2.3-fold. Peripheral plasma insulin levels were increased by 3.4-fold during the overnight period and by 4- to 5-fold during the two fed states. Endogenous insulin clearance was significantly reduced during feeding. Both low- and high-frequency insulin secretory pulsatilities were detected in the abdominally obese subjects. Pulse periods were within the normal range. Pulse maxima, nadirs, and absolute amplitudes were increased concomitant with the increase in insulin secretion. Ultradian relative pulse amplitudes, however, were blunted. A significantly higher pulse-to-pulse variability was observed in the abdominally obese subjects compared with normal subjects. Furthermore, a significantly higher level of interindividual variability in the nutrient-stimulated insulin secretion and in the ultradian pulse characteristics was observed. Thus in abdominal obesity, the increase in pancreatic insulin output is limited and the secretory pulsatilities are aberrant, suggesting a defect in the insulin secretory process. Diminished insulin clearance contributes to the degree of peripheral hyperinsulinemia compensating for the insulin resistance characteristic of this form of obesity.

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