Further studies on the absence of hypocalcemic effects of eel calcitonin in the eel, Anguilla japonica

Within 8 hr after an intraarterial injection of synthetic eel calcitonin (500 mU/100 g) into either freshwater- or seawater-adapted eels, no effect was observed on plasma Na, Ca, or Mg concentrations. In freshwater eels, a single injection of eel calcitonin (100 mU/100 g) into the caudal vein was without effect on ion concentrations of the urine or on blood pressure. There was no significant difference in plasma ion concentrations between freshwater eels infused with anticalcitonin rabbit serum and those infused with normal rabbit serum, although Ca and Mg concentrations decreased significantly after 3 days in both cases. There was also no difference in the circulating calcitonin levels between eels in fresh water and those in seawater. When the corpuscles of Stannius were removed from freshwater or seawater eels, plasma Ca concentration increased significantly after 2 to 4 weeks, whereas there was no change in the plasma calcitonin levels. Hypophysectomy of freshwater eels resulted in a significant decrease in plasma ion concentrations including Ca, but was without effect on plasma calcitonin levels. These observations indicate that calcitonin may play no significant role in maintenance of plasma Ca concentrations in the eel.