The stomach is the etiologic organ for immobilization-induced hypocalcemia in rats

Our previous study revealed that the gastric vagus nerve plays an etiologic role in immobilization (IMB) stress-induced hypocalcemia. The purpose of the present study is to identify exactly what parts of the stomach are involved in the development of IBM-induced hypocalcemia and to determine whether or not gastric acid secretion is involved. A total gastrectomy, but not a resection of the upper intestine, eliminated the hypocalcemic effect of IMB. In addition, either an antrectomy (removal of the source of gastrin) or a fundectomy (depriving the origin of gastric histamine and gastric acid) was sufficient for eliminating IMB-induced hypocalcemia, while a partial (50%) fundectomy failed to suppress it. An intraperitoneal injection of galanin (an inhibitor of gastrin release) or ranitidine (a blocker of histamine H2-receptor) also suppressed the calcium-lowering effect of IBM, whereas omeprazole (an inhibitor of the proton pump) had no effect. These findings suggest that the antrum and the fundus of the stomach play essential roles in IMB-induced hypocalcemia through the vagus-induced release of gastrin and histamine but not through the secretion of gastric acid per se.