Possible role and mode of action of gastrin on calcium homeostasis in the rat.

The hypocalcemic effect of gastrin and its possible mode of action were studied in rats. Gastrin (13 micrograms/100 g rat), injected intravenously led to a significant reduction in the plasma calcium concentrations. The release of endogenous gastrin by an intragastric phenylalanine instillation similarly led to a significant hypocalcemia in intact rat but not in antrectomized rat. Moreover, the protective role of endogenous gastrin against hypercalcemia induced by an intraduodenal infusion of CaCl2 (10 mg/100 g rat) was demonstrated. Gastrin (50 microgram/100 g rat) seems to have no influence on the net intestinal absorption of 45Ca. The removal of 45Ca from plasma was also unaffected by gastrin administration. The disappearance rate from plasma of 45Ca administered 17 hr previously was compared in sham, thyroidectomized (TX) and parathyroid-autotransplanted rats receiving saline or gastrin. The faster rate of disappearance of plasma 45Ca from plasma in gastrin-treated TX autoparathyroid-transplanted rats indicated the suppressive action of gastrin on the release of 45Ca from as yet unknown source(s).