β-Cell Function Relative to Islet Volume and Hormone Content in the Isolated Perfused Mouse Pancreas*

The β-cell function, total islet volume, and number were studied in 1- to 18-month-old mice, together with the extractable pancreatic insulin and glucagon. The β-cell function, determined as the total amount of insulin released in response to glucose from the in vitro perfused pancreas showed an agerelated increase, without any differences in the kinetics of insulin secretion between young and old mice. The total islet number and area in each individual pancreas was determined planimetrically after selective staining of the islets by perfusing the pancreas with dithizone. The islet area increased from 5.4 ± 1.7 mm2 at 1 month to 16.3 ± 2.1 mm2 at 18 months, whereas the number of islets remained virtually unchanged (1072 ± 51). Pancreatic insulin increased with age by nearly 500%, in contrast to a 35% reduction in pancretic glucagon. There was a strong relationship between body weight and total pancreatic DNA (P = 4.7 ×10-8), islet area (P = 3.2 × 10-7), insulin secretory capacity (P = 7 × 10-4), and total...