The mechanism of action and target organ of gastrin-induced hypocalcemia.

The hypocalcemia effect of gastrin and the possible role of the hormone in calcium homeostasis have been demonstrated in our previous study. The mechanism involves neither the gastrointestinal absorption nor the removal of calcium from plasma but is possibly due to the suppression of the calcium influx into blood. In searching for the organ(s) involved in the action of gastrin, the following were tested and not found to be directly responsible: stomach, intestine, pancreas, liver, spleen, adrenal gland, kidney, lung, muscle, and red blood cell. After 17 hr of 45Ca administration, the turnover of 45Ca in the tibia was measured. Gastrin was found to suppress the release of 45Ca by 25% within 1 hr. The suppressive effect of gastrin on 45Ca release was also demonstrated in an in vitro preparation which showed that the 45Ca released from prelabeled tibia into the incubating medium was also reduced by gastrin. It was thus concluded that the gastrin-induced hypocalcemia in rat was the result of a suppression of the release of calcium from bone.