Regulatory effect of endogenous calcitonin on calcium metabolism in hepatic bile system of rats.

The effect of calcium chloride (4.0 mg Ca2+/100 g BW) on the calcium metabolism in the hepatic bile system was investigated in intact and thyroparathyroidectomized rats. The administration of calcium did not alter the serum calcium of intact rats but increased it markedly in thyroparathyroidectomized rats. The administration of calcium to intact rats also caused a significant decrease in the liver plasma membrane Ca-ATPase activity, and a corresponding increase in liver calcium and bile calcium, while no such increase was seen in thyroparathyroidectomized rats. Meanwhile, the administration of calcitonin (CT, 80 MRC mU/100 g BW) to intact rats significantly lowered both serum calcium and liver plasma membrane Ca-ATPase activity, and it also significantly elevated both liver and bile calcium. These results suggest that endogenous CT regulates calcium metabolism in the hepatic bile system of rats after the injection of calcium chloride.