Gradual delay in glucose-induced first phase insulin secretion by the pancreatic islets of 7 week-, 6 month-, and 1 year-old rats.

The temporal profiles of insulin secretion by isolated pancreatic islets of male Wistar rats with various ages up to 1-year-old were studied using high glucose, potassium (K+) depolarization, and arginine as secretagogues. In the islets of 6-month-old rats, the onset and peak of glucose-induced first phase of insulin release were delayed for 1 min compared to those of 7--week-old rats. The onset and peak were further delayed for 1 min in the islets of 1-year-old rats. The onset of glucose-induced second phase of insulin secretion, and the onset and peak of K+ depolarization- and arginine-induced insulin release were not delayed in the islets of 6-month and 1-year-old rats. Glucose-stimulated increase in cytosolic free calcium ([Ca2+]i) seemed not delayed in the islets of 1-year-old rats. We conclude that the first phase of glucose-induced insulin release by the islets is selectively delayed as rat ages. It was suggested that the defect lies distal to the elevation of [Ca2+]i.