Ionized calcium influences gastrin stimulated histamine release and acid secretion, but not histamine stimulated acid output in the totally isolated vascularly perfused rat stomach.

When changing from bovine serum albumin to dextran T70 as colloid without adjusting the total calcium concentration in the vascular perfusate of the totally isolated vascularly perfused rat stomach, we noticed a drastic fall in gastrin-stimulated acid secretion. In the present study the effect of the two colloids on ionized calcium in the vascular perfusate as well as the effect on acid secretion and vascular histamine release were studied. There was no difference in gastrin-stimulated acid secretion or vascular histamine release between the two colloids after adjusting the total calcium concentrations so that ionized calcium was similar. Whereas baseline acid secretion showed no marked dependency of ionized calcium within the range tested (0.73-1.54 mmol l-1, gastrin-stimulated acid secretion was highly dependent on ionized calcium being reduced at the higher concentration of Ca2+. Histamine stimulated acid secretion, on the other hand, was virtually unaffected by the concentration of ionized calcium in the same range. Like gastrin-stimulated acid secretion, gastrin-stimulated histamine release was inhibited at higher Ca2+ concentrations. Thus, elevated Ca2+ concentrations seemed to reduce gastrin-stimulated acid secretion by inhibiting vascular histamine release.