[Exocrine pancreatic function and calcium balance. Experimental studies of the effect of parathyroid hormone, vitamin D3, 25-hydroxycholecalciferol, dihydrotachysterin and thyrocalcitonin (author's transl)]

Immunohistochemical localization of the 1,25(OH)2D3 receptor and calbindin D28k in human and rat pancreas

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] is required for normal glucose-stimulated insulin release from pancreatic beta-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 beta-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 D28k, 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 D28k 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 D28k are present in human pancreatic tissue. VDR and calbindin D28k 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.

Effects of acute hypercalcemia on exocrine pancreatic secretion in the cat

To investigate the effects of acute hypercalcemia on exocrine pancreatic secretion, anesthetized cats were given calcium intravenously. Increasing hypercalcemia (3.7-6.3 mmol/L) evoked a dose-dependent increase in enzyme output that was 12 times greater than in normocalcemic controls (p less than 0.001) and was 60% of subsequent maximal stimulation with intravenous cholecystokinin (CCK). The effect of hypercalcemia on enzyme secretion was abolished when CCK was administered 60 min before calcium and at a dose to cause maximal enzyme output. Atropine did not prevent the calcium-induced increase in enzyme secretion. Pancreatic fluid and bicarbonate outputs were not influenced by hypercalcemia during intravenous administration of small amounts of secretin, but were increased by addition of CCK to the secretin infusion. Hypercalcemia did not induce macroscopic or light-microscopic changes in pancreatic morphology. Plasma levels of both CCK and gastrin were increased (p less than 0.01) during hypercalcemia, with and without precalcium administration of CCK; atropine significantly inhibited (p less than 0.05), but did not abolish the calcium-induced releases of both peptides. These data suggest that in the anesthetized cat, acute hypercalcemia induced by intravenous calcium infusion stimulates pancreatic secretion of enzymes, but not fluid and bicarbonate. Acute hypercalcemia also causes release of CCK and, as shown previously, gastrin. The findings suggest that the stimulatory effect of hypercalcemia on pancreatic enzyme secretion is not dependent on intact cholinergic pathways and is probably not exclusively mediated by release of CCK or gastrin.

Interactions of calcium, magnesium and atropine on exocrine pancreatic secretion in man

The effects of the intravenous administration of atropine or magnesium on pancreatic secretion which has been stimulated by secretin and induced hypercalcaemia have been studied in man. In the presence of secretin (0.5 CU/kg.h) the infusion of Ca2+ (0.3 mmol/kg.105 min) resulted in an increase in secretion of enzymes by 100-200%, and in that of Ca2+ and Mg2+ by 50-100% without affecting fluid and bicarbonate secretion. The additional injection of atropine (0.5 mg i.v. and 0.5 mg s.c.) were followed by a prompt fall in enzymes but not in Ca2+ and Mg2+ to the secretin-stimulated values. The additional infusion of Mg2+ (0.12 mmol/kg.45 min) to the Ca2+-infusion did not alter the secretion of enzymes, Ca2+ or Mg2+ compared with the calcium infusion alone. It is suggested that the hypercalcaemic stimulus depends on an intact innervation of the acinar cells. In these experiments the secretion of Ca2+ and Mg2+ seem to originate mainly from extracellular fluxes.