Hormone secretion by isolated perfused pancreas of aging Fischer 344 rats

This is the first study investigating hormone secretion by the isolated perfused pancreas of the aged Fischer 344 rat. Nutrient-induced release of insulin, glucagon, and somatostatin in overnight-fasted rats aged 2, 10, 18, 24, and 30 mo was studied. After an equilibration period, the pancreas was perfused for 20 min with buffer A (containing 4.2 mM glucose plus a 3.5 mM mixture of amino acids) then for 20 min with buffer B (containing 8.3 mM glucose and 7.0 mM amino acids). When stimulated by buffer B, the amount of insulin secreted increased (P less than 0.05) from immaturity (2 mo) to adulthood (10-18 mo) because of growth of the organ. From adulthood to very old age an equal amount of insulin was released in all groups during the last 19 min of perfusion with buffer B. Fasting blood glucose levels remained constant throughout life, whereas pancreatic insulin stores and plasma insulin levels rose, reaching peak values at 18 mo. The alpha-cell appeared to be deemphasized relative to the beta-cell during development but not thereafter, as indicated by the findings that from immaturity to adulthood pancreatic glucagon stores expanded less than insulin stores and that glucagon release significantly decreased. Only minor changes in somatostatin release from the delta-cells were observed after the rat reached adulthood. We conclude that the endocrine secretory response of the pancreas is well maintained throughout life in the Fischer 344 rat.