Abstract
1. The actions of secretin, cholecystokinin-pancreozymin (CCK-PZ) and caerulein have been studied on the rate of flow and protein secretion from the pancreas of urethane-anaesthetized rats.2. Secretin stimulated the rate of flow of pancreatic juice and also stimulated the secretion of small but significant quantities of protein. Cholecystokinin-pancreozymin and caerulein strongly stimulated both the rate of flow and rate of protein secretion.3. Maximal peak rates of flow of juice stimulated by CCK-PZ (20.3 mul./5 min), were significantly higher than stimulated by secretin (14.0 mul./5 min), but maximal volumes of pancreatic juice secreted in total response to rapid I.V. injections of secretin and CCK-PZ were not significantly different.4. The time course of rates of flow of juice stimulated by CCK-PZ and caerulein were different to those stimulated by secretin. With CCK-PZ and caerulein peak rates occurred earlier and responses declined sooner than with secretin.5. The actions of CCK-PZ, caerulein and secretin on the pancreas of the rat are discussed in the light of the responses evoked in other species. It is concluded that the rat is less sensitive than other spieces to secretin but not CCK-PZ.