Possible Role and Mode of Action of Gastrin on Calcium Homeostasis in the Rat

Abstract

The hypocalcemic effect of gastrin and its possible mode of action were studied in rats. Gastrin (13 μg/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 μg/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-auto transplanted 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).