INFLUENCE OF HYPERCALCEMIA ON IONIZED CALCIUM-CONCENTRATION IN PANCREATIC-JUICE OF THE DOG

Calcium concentration of pancreatic juice depends on secretion of calc ium bound to enzymatic proteins or calcium diffusion from interstitial fluids. To evaluate the relative magnitude of these pathways, we stud ied the influence of hypercalcemia on ionized calcium (Ca++) in dog pa ncreatic juice. Pancreatic juice was collected during basal secretion and during stimulation by secretin or secretin plus caerulein in contr ol conditions and under CaCl2 infusion. [Ca++] was measured by selecti ve electrodes. Saturation of juice in CaCO3 was calculated. In stimula ted juice, total calcium concentration ([Ca-T]) and [Ca++] were unchan ged by hypercalcemia. In basal juice, composition was profoundly modif ied by hypercalcemia because [Ca-T] (3.31 +/- 0.89 mmol/L vs 1.80 +/- 0.44 for controls), [Ca++] (1.44 +/- 0.37 mmol/L vs 0.84 +/- 0.24 mmol /L for controls), and the index of saturation in CaCO3 (5.2 +/- 2.4 vs 2.9 +/- 1.8 for controls) increased significantly. Protein concentrat ion was unchanged. This suggests that in basal conditions, the relatio nship between plasma and juice calcium levels is due to passive inters titial Ca++ diffusion through the pancreatic ducts. In accordance with the hypothesis of a restricted calcium diffusion, the effects of hype rcalcemia were flow rate dependent, being less pronounced when basal f low rate increased. It is concluded that, in the dog, the calcium spec ies found in stimulated juice result from a redistribution of calcium secreted along with proteins, whereas at low secretion rate, juice cal cium level depends mainly on interstitial Ca++ diffusion into the main pancreatic ducts.