Mechanism of cholecystokinin-A-receptor antagonist on human pancreatic exocrine secretion - Localization of CCK-A receptor in the human duodenum

Expressions of the cholecystokinin (CCK)-A and -B receptor genes in human duodenum, pancreas and gallbladder were examined by Northern blot analysis and reverse transcriptase polymerase chain reaction (RT-PCR) followed by Southern blot hybridization. The autoradiographic study of CCK-A and -B receptors in the human duodenum and pancreas was examined in vitro. To determine the subtypes to CCK receptors in the pancreas or duodenum, we studied the abilities of CCK-A and -B receptor agonists (CCK-8 and gastrin) and antagonists (loxiglumide, L-364,718 and L-365,260) to inhibit binding of I-125-CCK-8. CCK-A receptor mRNA was not expressed in the human pancreas, but was expressed in the gallbladder and duodenum, although it was expressed in the pancreas by RT-PCR. CCK-B receptor mRNA was expressed in the pancreas, but not in gallbladder and duodenum, Using autoradiography, high concentrations of CCK-A receptors were detected in the duodenal mucosa, although in the pancreas only CCK-B receptors were detected by this method. These results suggest that localization of CCK-A receptor in human duodenum provides a biochemical and morphological basis for some physiological functions of CCK.