Pancreatic exocrine enzymes during the neonatal period in postmature rats.

Pancreatic content of exocrine enzymes in newborn rat pups shows a sharp decline soon after birth. To investigate if this decline is a preprogrammed and, therefore, inherently controlled phenomenon, or a result of external stimulus, prolonged gestation, or postmaturity (2 extra days in utero) in pregnant dams was induced by daily subcutaneous injection of progesterone from the 20th to 22nd days of gestation. Postmature pups showed the same high levels of lipase, trypsin(ogen), and amylase as control pups at birth. They also exhibited the same decline in these enzymes as control pups by the 2nd day after birth, suggesting that it is a response to external stimulus. Pups prevented from suckling retained the high levels of lipase, amylase, and trypsin(ogen) by the 2nd day. The stimulus, therefore, appeared to be the initiation of suckling. Pups prevented from suckling but given 5% glucose water orally every 4 h starting from birth for 24 h showed a sharp decline in amylase with only slight decreases in lipase and trypsin(ogen) by the 2nd day. The components in the feed, therefore, also seem to be an important determinant for selective enzyme release from the pancreas of the neonates. Electron microscopic studies revealed a sharp decrease in the number of zymogen granules in the continuously-suckled pups as compared to age-matched non-suckled counterparts. The reduction in enzyme content thus is the result of secretion in response to suckling.