The excretion of salt load by the developing chick embryo

Salt loads (0.17 or 0.34 mmol Na+; 6 M NaCl solution labelled with 24Na) were administered into the amniotic fluid of 7-day-old chick embryos. 24Na distribution in the embryonic blood, amniotic and allantoic fluids was measured in 1, 2, 4, 8, 12 and 24 h intervals to assess the kinetics of salt load movements in particular egg compartments. The aim was to estimate the efficiency of the embryonic homeostatic apparatus to maintain ionic balance inside th embryonic body. The Na+ concentration in the amniotic fluid was expected to rise after salt loading by about 275 and 400 mM, respectively. More than 10% of the salt dose per ml appeared in the embryonic blood 2 h after salt load administration while only 0.2% were found in the urine (collected as allantoic fluid). The maximal rise of 24Na activity in the blood of salt-loaded embryos reached 11 to 12% of the dose which corresponded to an increase in Na+ concentration by 19 and 41 mM, respectively. The maximum of 24Na activity appeared in the allantoic fluid with a delay of several hours and indicated an increment of Na+ concentration by 6% and 9% of the dose per ml in the case of salt-loaded embryos. The Na+ concentration in the allantoic fluid (urine) never exceeded that in the blood. The final Na+ activity (estimated in the blood 24 h after salt loading) was equal to 5% of the dose per ml in both cases, indicating a persistent elevation of Na+ concentration by 8.6 and 17.2 mM, respectively. (author). 1 fig., 2 tabs., 8 refs