Pancreatic CCKB receptors: their potential roles in somatostatin release and δ-cell proliferation

In rodents, cholecystokinin (CCK) induces pancreatic enzyme secretion and pancreas growth through its CCKA receptors. It is unknown whether occupation of the CCKB receptors present in pig and human pancreas can cause the same effects. This study evaluates CCKB receptor expression in rat, mouse, pig, and fetal human pancreata using Northern blot, Western blot, and immunofluorescence techniques. The reported 2.7-kb CCKBreceptor mRNA transcript in the rat brain and gastric fundus is absent in pancreas; the message was, however, detected by RT-PCR and by a CCKB receptor antibody as an 80-kDa protein present uniquely in islet δ-cells. Proteins of 50 and 80 kDa appear in mouse pancreas, and proteins of 50 and 115 kDa appear in pig and human pancreas, respectively, all localized in islet δ-cells. Gastrin mRNAs are strongly present in fetal rat pancreas, and the hormone is localized in islets; both are repressed 10 days after birth. In conclusion, the CCKB receptors are present in pancreas of four species with exclusive location in islet δ-cells. In such a location, they could be indirectly involved in the control of enzyme secretion.