D

CCK, gastrin and secretin are all recognized stimulants of the exocrine pancreas (CCK → enzyme-rich juice; secretin → bicarbonate-rich juice; gastrin produces a mild enzyme response). In contrast, gastric inhibitory polypeptide (GIP) primarily modulates gastric acid and potentiates insulin release and has been shown to have little or no effect on pancreatic exocrine secretion, even when given in pharmacologic doses [Yamagishi, 1980, PMID 6445850].