Jinnosuke Abe

Ultimobranchial Calcitonin of Anguilla Japonica

This chapter provides the results of studies conducted to observe calcitonin activity in the ultimobranchial body of Anguilla japonica. Calcitonin has been extracted from the ultimobranchial body (UBB) of various species of lower vertebrates. Data indicate that calcitonin plays an important role in the regulation of osmotic pressure in this species. In Anguilla japonica, UBB is usually located as an unpaired organ with a rather wide distribution between the esophagus and the pericardium. A part of the UBB is also found within the pericardium and esophagus. Calcitonin is secreted from the thyroid in mammals and from the UBB in birds, reptiles, amphibians, and fish. It has been well known that Anguilla japonica moves into sea water for spawning and then returns into fresh water. When eels are transferred from fresh water to sea water, there is an increase in both serum calcium and osmotic pressure. Calcitonin plays some role in the calcium metabolism in Anguilla japonica, but its mode of action probably differs markedly from that in mammals.