Abstract
The effect of calcitonin (CT) on Ca-ATPase activity in the plasma membrane fraction of rat liver was investigated. CT (80 MRC mU/100g BW) administered subcutaneously to rats, caused a significant decrease in serum calcium, while increasing liver calcium. The administration of CT produced a rapid decrease of Ca-ATPase activity in the plasma membrane fraction of liver, whereas CT did not cause a significant alteration of p-nitrophenyl phosphatase activity. The maximal response of CT was obtained with 80 MRC mU/100g BW. Meanwhile, the administration of imidazole (30mg/100g BW) which has a hypocalcemic effect, like CT, produced a significant increase in liver calcium and a corresponding fall in Ca-ATPase activity of the plasma menbrane fraction. The reduction of Ca-ATPase activity produced by imidazole was significantly potentiated by the simultaneous administration of CT, and the rise in liver calcium was enhanced slightly. The present results suggest that the action of CT on liver calcium involves the decrease of Ca-ATPase activity in the plasma membrane of rat liver.
