Prolonged in vivo stimulation of the rat exocrine pancreas by caerulein infusion. Biochemical effects.

Chronic secretory stimulation of the rat exocrine pancreas by continuous infusion of 0.1825 nmol/kg . h caerulein for 4 to 8 days as well as by a dose increased fivefold after the first 3 days of treatment results in three clearly distinct modes of pancreatic reaction apparently independent of the treatment pattern. One group of animals developed degranulation of acinar cells, low enzyme content, and accelerated intracellular transport and discharge of newly synthesized proteins as expected after secretory stimulation. A second group exhibited a striking overgranulation of acinar cells and extremely high enzyme content. In vitro intracellular transport rates were normal and zymogen output per cell in response to caerulein stimulus was elevated. The third group developed apparent desensitization towards hormonal stimulus in vivo. Enzyme content was slightly elevated and secretory behaviour in vitro similar to controls. Basal secretion rates were elevated in most pancreata of all 3 groups, possibly due to persistence of stimulatory effect of caerulein given in vivo up to the moment of sacrifice. Enzyme composition was strikingly changed in favor of the proteases trypsinogen and chymotrypsinogen in all pancreata.