Haemodynamic and exocrine effects of caerulein at submaximal and supramaximal levels on the rat pancreas: role of cholecystokinin receptor subtypes.

BACKGROUND: We have investigated the involvement of cholecystokinin (CCK) receptor subtypes in haemodynamic changes in the pancreas of anaesthetized rats during submaximal and supramaximal stimulation with the CCK analogue, caerulein. METHODS: For submaximal stimulation, caerulein (0.4 nmol/kg/h) was infused intravenously, while acute pancreatitis was induced by intraperitoneal injections of high doses of caerulein (3 x 25 nmol/kg). Pancreatic blood flow was measured by hydrogen clearance. RESULTS: Low caerulein doses increased pancreatic blood flow by 26 +/- 8% and vascular conductance by 24 +/- 4%. This effect was mimicked by the CCK2 agonist gastrin-17. All effects were abolished by a CCK2 antagonist while a CCK1 antagonist remained inactive. Conversely, amylase output by caerulein was abolished by CCK1 receptor blockade, but not by inhibition of CCK2 receptors. During caerulein-induced pancreatitis, vascular conductance increased by 109 +/- 26% and remained elevated throughout the experiment; vascular flow initially increased by 62 +/- 27% and then returned to baseline. The vascular effects were prevented by a CCK2 receptor antagonist, while the induction of pancreatitis was due to CCK1 receptor stimulation. CONCLUSIONS: Caerulein increases pancreatic vascular flow via activation of CCK2 receptors. This effect occurs both at submaximal and at supramaximal levels of exocrine stimulation.