Ontogeny of endocrine control of osmoregulation in chick embryo : II. Actions of prolactin, arginine vasopressin, and aldosterone

Abstract

Actions of ovine prolactin (oPRL), arginine vasopressin (AVP), and aldosterone on volume of allantoic fluid and its Cl- concentration and on renal Na+-K+-ATPase activities in mesonephros and metanephros were examined at various times during ontogeny of the chick embryo. Ovine PRL decreased allantoic fluid volume and lowered Cl- concentration in this compartment when injected for various periods prior to 14 days of incubation. After this time, when endogenous PRL levels become elevated (Day 16), exogenous oPRL no longer altered allantoic fluid volume or Cl-. Ovine PRL also stimulated Na+-K+-ATPase activity in the metanephros when embryos were treated before 14 days of incubation but did not stimulate the transport enzyme in mesonephros. Stimulation of metanephric Na+-K+-ATPase was a direct action of oPRL since this activity was also stimulated by the hormone in metanephros maintained in organ culture for 3 days. PRL did not stimulate Na+-K+-ATPase in organ-cultured mesonephros, and it failed to stimulate Na+-K+-ATPase in metanephros of juvenile chickens treated after hatching. Injection of AVP, a known contaminant of the NIH-oPRL used in these experiments, duplicated some, but not all actions of oPRL in the embryo. Like oPRL, AVP reduced the Cl- concentration of allantoic fluid, but AVP did not mimic the effect of oPRL in stimulation of metanephric Na+-K+-ATPase activity. Thus, oPRL preparations appear to possess osmoregulatory actions in the embryo which can be distinguished from actions attributable to the contaminant, ADH. Aldosterone injected prior to 16.5 days of incubation depressed activities of Na+-K+-ATPase and Mg2+-ATPase in mesonephros, but did not alter these enzyme activities in metanephros. The depressed enzyme activities induced by aldosterone in mesonephros may have been, in part, a toxic response to the hormone as control injections of cholesterol had comparable effects. On the other hand, aldosterone specifically stimulated Ca2+-dependent ATPase(s) and succinate dehydrogenase in metanephros. The three principal osmoregulatory hormones of adult birds, PRL, ADH, and aldosterone, seem to be active also during ontogeny of the avian embryo, with mesonephric and metanephric kidneys as target organs.