Action des hormones neurohypophysaires sur les échanges de sodium (mesurés à l'aide du radio-sodium Na 24) chez un téléostéen euryhalin: Platichthys flesus L

Abstract

Techniques for the measurement of sodium exchange in the euryhaline flounder Platichthys flesus, either adapted to sea or to fresh water or when undergoing a change from fresh to sea water, are described, as are the theoretical bases for these calculations. In the flounder adapted to fresh water the influx and outflux of sodium are in the order of 1 mg/100 gm body weight/hr, that is the sodium exchange involves at the most 1% of the exchangeable sodium per hour. The injection of oxytocin produces a transitory increase of the outflux and a more lasting increase of the influx of sodium. In the flounder adapted to sea water the sodium exchange is considerably greater, being in the region of 25% of the exchangeable sodium per hour (about 33 mg/100 gm body weight/hr). Oxytocin increases the rate of exchange to an average of 47 mg/100 mg/hr, i.e., 35% of the exchangeable sodium. Lysine vasopressin has no effect. Fish transferred from fresh water to sea water show a progressive increase of the sodium outflux. This augmentation is most rapid in small individuals and in fishes that have only been subjected to a short preliminary period of adaptation to fresh water. Oxytocin accelerates the increase of sodium outflux associated with the change of milieu. It seems probable that the neurohypophysial hormones intervene in the mineral regulation of this euryhaline fish by increasing the sodium absorption by the gills in fresh water and sodium excretion in sea water.