Action of Neurohypophyseal Hormones on the Sodium Fluxes of a Freshwater Teleost

Abstract

THE presence of hormones showing oxytocic and vasopressic activities in the neurohypophysis of teleosteans has been known for some time¹. The intervention of the hypothalamo–hypophyseal complex in the regulation of the hydro-mineral balance in teleosteans has been recently proposed as a result of histological studies on neurosecretion². The biological role of the hormones secreted by this complex, however, remains unknown : no antidiuretic or water-balance effect has been shown in these animals³. On the other hand, teleostean neurohypophyseal extracts are known to be active in certain Amphibia not only on the water metabolism⁴, but also on the active sodium transport exhibited by the skin⁵. The object of the present work was to study whether, failing a clear-cut effect on water metabolism, the role of these hormones in fish is in fact concerned with sodium exchange across the gills.