The effect of cholecystokinin‐related peptides on periodic pancreatic secretion in fasting dogs.

1. The effect of cholecystokinin octapeptide (CCK‐8) and pentagastrin on periodic pancreatic secretion was studied in fasting conscious dogs. 2. Both CCK‐8 and pentagastrin, in small doses, prolonged the interval of periodic pancreatic secretion. Periodicity was disrupted by large doses of CCK‐8 and pentagastrin. 3. CCK‐8, at the dose which did not disrupt the cycle, raised the peak and the valley‐to‐valley means, but not the valley mean, of protein secretion in one cycle. Except at large doses, pentagastrin failed to increase the peak and valley mean, but increased mean, valley‐to‐valley protein secretion. Large doses of both pentagastrin and CCK‐8 increased protein secretion at the valley. 4. The peak of periodic pancreatic protein secretion was about half the observed maximum protein response to CCK‐8. 5. Atropine reduced pancreatic fluid and protein responses to small doses of CCK‐8 to the levels of valleys. At large doses, however, both responses were augmented by atropine. Hexamethonium reduced the responses to any dose of CCK‐8 to valley levels or less. Volume and protein responses to pentagastrin following atropine or hexamethonium were of similar magnitude to those at valleys. 6. It is concluded that CCK‐8 and pentagastrin stimulate pancreatic enzyme secretion directly by acting on acinar cells and indirectly by modifying cholinergic ganglionic activities which control periodic secretion in conscious dogs.