Influence of pancreatic ducts on saturation of juice with calcium carbonate in dogs

Abstract

In several species, bicarbonate and calcium concentrations of pancreatic juice are known to vary during the different phases of pancreatic secretion. The effects of these variations on the saturation of juice with calcium carbonate, a critical factor for the formation of pancreatic stones, are not known. In this work, we studied the saturation degree of pancreatic juice with calcium carbonate in six unanesthetized beagle dogs equipped with Thomas cannulae during basal secretion and after bolus injections of cerulein (30 ng/kg) or secretin (0.25 units/kg). In the different samples of pure pancreatic juice, pH, PCO2, bicarbonate, and proteins were measured by standard methods. Total calcium (CaT) and ionized calcium (Ca2+) were determined using calcium-specific electrodes. Saturation with calcium carbonate was calculated by reference to the solubility product of calcite at 37 degrees C. Almost all the samples were found to be supersaturated with calcium carbonate but large variations of the saturation index were observed. In basal samples, obtained during periods of low secretion rate, the mean saturation index (3.35 +/- 3.01) was significantly lower than under secretion (12.10 +/- 5.14) or cerulein (18.01 +/- 8.42). This low basal saturation index, in spite of a high Ca2+ content, was explained by a low bicarbonate concentration (37.6 +/- 18.9 mmol/liter) and a high PCO2 (13.4 +/- 7.5 kPa). In contrast, in juice obtained after hormonal stimulation, PCO2 (4.8 +/- 1.6 kPa) was similar to plasma PCO2 (5.5 +/- 1.2 kPa).(ABSTRACT TRUNCATED AT 250 WORDS)

ATP-consuming and ATP-generating Enzymes Secreted by Pancreas

“…In any case, enzyme release, however it happens, seems to be regulated. In pancreatic juice, where normal concentrations of free Ca 2ϩ and Mg 2ϩ are submillimolar (33,34), the conditions for enzymes would be suboptimal when compared with in vitro enzymatic assays. Nevertheless, since the juice emerging out of the organ/cannula has relatively low ATP concentrations when compared with estimated concentrations released from acini ( Fig.…”

Molecular and Functional Identification of a Ca2+ (Polyvalent Cation)-sensing Receptor in Rat Pancreas

“…Because the incidence of pancreatic stone formation is surprisingly low, it has been postulated that homeostatic responses must be activated to reduce lithogenic potential. A number of suggestions have been advanced for candidate mechanisms, all within the ductal system, including increased H ϩ and fluid secretion and a reduction in bicarbonate production (1). However, thus far there is no direct experimental evidence for any of these hypotheses, and the question of how the pH and the free Ca 2ϩ concentration in pancreatic juice are regulated is yet to be understood.…”

“…The juice also contains millimolar quantities of Ca 2ϩ ions, which are released from secretory granules along with pancreatic zymogens (1). The presence of these ions means that the pancreatic juice is at risk of precipitating calcium stones, which are a major cause of chronic pancreatitis (1).…”

“…Pancreatic juice in humans and other species is an alkaline secretion, containing up to 140 mM bicarbonate ions (1). The juice also contains millimolar quantities of Ca 2ϩ ions, which are released from secretory granules along with pancreatic zymogens (1).…”

“…Recently Brown et al (2) have identified a cell-surface, G protein-linked Ca 2ϩ (polyvalent cation)-sensing receptor (CaR) 1 which is capable of monitoring even minute changes in extracellular calcium concentration ([Ca 2ϩ ] o ) and responds with an increase in intracellular calcium concentration ([Ca 2ϩ ] i ). The receptor is sensitive to changes in [Ca 2ϩ ] o in the millimolar range, compatible with [Ca 2ϩ ] o in the plasma.…”