Immunohistochemical localization of the 1,25(OH)₂D₃ receptor and calbindin D(28k) in human and rat pancreas

1,25-Dihydroxyvitamin D₃ [1,25(OH)₂D₃] is required for normal glucose- stimulated insulin release from pancreatic β-cells. Biochemical characterization techniques have demonstrated the presence of the 1,25(OH)₂D₃ receptor (VDR) in homogenates of whole pancreas. Autoradiographic studies using radiolabeled 1,25(OH)₂D₃ suggest that the VDR is localized to β-cells but are inconclusive. We used immunohistochemical techniques to stain serial sections from both human and rat pancreas with polyclonal antibodies to human VDR, chick calbindin D(28k), insulin, glucagon, and somatostatin. VDR was present in the islet cells and also at low levels in acinar cells of the human and rat pancreas. Calbindin D(28k) was distributed in a manner similar to the VDR in pancreatic islets but was not present in acini. These results show for the first time that VDR and calbindin D(28k) are present in human pancreatic tissue. VDR and calbindin D(28k) are focally distributed throughout pancreatic islet cell types in humans and rats; VDR is also present in the exocrine pancreas. These findings suggest that 1,25(OH)₂D₃ may influence both endocrine and exocrine pancreatic function.