Pancreatic Insulin-, Glucagon-, and Somatostatin-Positive Islet Cell Populations during the Perinatal Development of the Rat

Pancreatic insulin-, glucagon- and somatostatin-positive islet cell volumes were quantitated morphometrically during the developmental interval from 16 days post coitum to 10 days postnatal. There was a rapid increase in the alpha- and beta-cell populations during late fetal life. The beta-cells increased more rapidly and comprised the major portion of the islets after the 20th fetal day. After birth the rate of increase of both beta- and alpha-cells decreased but was greater than that of the surrounding exocrine pancreas during the early period of postnatal life. This resulted in an islet cell percentage of 5-6% of the total pancrease on day 6 postnatal. delta-Cells were present before birth but increased in volume density within the islet cell after birth. The implications of these morphological data to the interpretation of physiological studies are discussed.