Pathogenesis of pancreatic and biliary CaCO3 lithiasis: the solubility product (K'sp) of calcite determined with the Ca++ electrode.

There are three digestive secretory fluids with high bicarbonate and high pH values: bile, pancreatic juice, and saliva. Each is subject to development of CaCO3-containing stones. In bile, calcium precipitation is a requisite event in the initiation and growth of all pigment gallstones and is postulated to initiate cholesterol gallstone formation by forming a nidus for cholesterol precipitation. In the pancreas, stones in both humans and cattle are composed largely of calcite. Knowledge of appropriate solubility product constant (K'sp) values is essential in defining lithogenicity in each of these secretions. Only two studies of calcite solubility at physiologic total ionic strength (u) have been found, both of which used total calcium measurements to estimate free Ca++ ion in calculating K'sp. The Ca++ electrode has allowed a fresh appraisal of this problem. Studies of calcite were made at 24 degrees C and 37 degrees C and u = 0.16 mol/L over an 11-day period. At each temperature, pH declined slightly with time, reflecting atmospheric CO2 uptake. As predicted by theory, this decline was associated with increase in free Ca++ ion and total calcium concentration, but K'sp remained constant because of corresponding decline in [CO=3]. Mean K'sp at 24 degrees C was 1.33 +/- 0.04 X 10(-8) mol/L, and at 37 degrees C it was 3.76 +/- 0.09 X 10(-8) mol/L. A lithogenicity diagram, applicable to bile, pancreatic juice, saliva, plasma, and other body fluids at u = 0.16 mol/L, is presented for [Ca++]sat, the free Ca++ ion concentration at the limit of a stable thermodynamic state.(ABSTRACT TRUNCATED AT 250 WORDS)