Effects of calcitonin on plasma calcium and phosphate in the mudskipper, Periophthalmodon schlosseri (Teleostei), in water and during exposure to air.

After 7 days in air on wet filter paper mudskippers had normal body weight and normal levels of plasma sodium, potassium, and phosphate. They were, however, significantly hypercalcemic. The hypercalcemia could be reduced by the daily intraperitoneal injection of synthetic eel calcitonin (1.67 microgram kg-1 day-1) and this effect was dose dependent with a maximal response at a dose of 3.33 micrograms kg-1 day-1. Calcitonin had no effect on plasma calcium levels of fish held in water but did induce significant hyperphosphatemia whether the fish were held in water or in air on wet filter paper with this effect being greater under the latter conditions. The hypocalcemic action of calcitonin was restricted to conditions under which the fish displayed patent hypercalcemia. Under no conditions did calcitonin produce significant hypocalcemia so it appears that the action of synthetic eel calcitonin in the mudskipper, Periophthalmodon schlosseri, is dependent upon the presence of excess plasma calcium and is thus more accurately described as being anti-hypercalcemic rather than hypocalcemic.