Pancreatic secretory response to cholecystokinin-pancreozymin and caerulein in the conscious rat.

Abstract

1. The effects of graded intravenous doses of cholecystokinin (CCK) and caerulein on exocrine pancreatic secretion have, been assessed in conscious rats. Bile and pancreatic juice were separately returned to the duodenum between and during tests. 2. Low doses of CCK (from 417 to 3,335 ng kg−1 h−1) or caerulein (from 37.5 to 150 ng kg−1 h−1) slightly increased flow rate but increased K+ and HCO 3 − outputs to a greater extent, without altering Cl− output. The sum of the anion concentrations (Cl−+HCO 3 − ) stayed constant, which explains the decrease in Cl− concentration when the HCO 3 − concentration increased. 3. High doses of CCK (6,670 and 13,335 ng kg−1 h−1) and of caerulein (600 ng kg−1 h−1 strongly inhibited volume flow and outputs of all the ions, and the sum of the concentrations of anions fell. 4. Protein concentration and output increased with the same time course in response to both CCK and caerulein, i. e. course in response to both CCK and caerulein, i. e. a sustained stimulation during infusion, without any delayed inhibitory effect afterwards. The increase followed a linear dose-response relation to both CCK and caerulein. D50 was approximately 1,000 ng kg−1 h−1 for CCK and 95 ng kg−1 h−1 for caerulein. The maximal secretory rate of protein in our experiments was obtained with 300 ng kg−1 h−1 caerulein (20.27 mg 30 min−1) and was almost twice that obtained with CCK (10.6 mg 30 min−1) which suggests that the most potent agonist is a shorter derivative of CCK. Finally, both hormones decreased protein output at supramaximal levels. 5. It is concluded that both CCK and caerulein have similar effects on pancreatic secretion in the conscious rat and in other species. However, the conscious rat differs from other species in that water, HCO 3 − and K+ secretions are stimulated by low doses of agonists. In contrast, high doses of agonists inhibited all components of secretion.