The Effect of Environmental Calcium and Ovine Prolactin on Sodium Balance in Fundulus Kansae

The ability ofFundulus kansae to live in both fresh water and 200% sea water, even when hypophysectomized, makes it a convenient experimental animal. In a previous paper it has been demonstrated that the permeability of the fish to water is affected both by ovine prolactin and by the concentration of calcium ions present in the medium (Potts & Fleming, 1970). Calcium ions have an effect on the permeability to water independent of prolactin and serve to reduce the permeability to water. Hypophysectomized fish had a lower permeability to water than intact fish, especially in fresh water, where prolactin production is highest, and prolactin restored the water permeability of hypophysectomized fish to normal levels. The higher permeability to water of fish adapted to fresh water (Potts, Foster, Rudy & Howells, 1967; Evans, 1969) is due to the combined effects of a high internal concentration of prolactin and a low external concentration of calcium ions. Calcium ions are known to effect the permeability of biological membranes to other ions. The fluxes of sodium ions through fish adapted to sea water are much higher than those seen in fish adapted to fresh water, and transfer from one medium to another is usually associated with dramatic changes in flux, but the significance of such changes is not entirely understood (Motais, Garcia Romeu & Maetz, 1966; Potts, Foster & Stather, 1970). The effects of calcium ions on the flexus of sodium through F. kansae in various media have therefore been investigated.