[Relationship between electrolyte balance and the function of the renin- angiotensin-aldosterone system in fetuses and neonates (author's transl)].

In order to establish the relationship between renin-angiotensin-aldosterone (R-A-ALDO), water and electrolyte balance in fetuses and neonates, a series of their plasma levels were evaluated concurrently and the following results were obtained. Neonates at delivery with birth weights in excess of 3.0 kg, consistently showed high umbilical plasma levels of ALDO, deoxycorticosterone (DOC), plasma renin activity (PRA) and angiotensin-II (A-II). Potassium (K+), sodium (Na+) and chloride (Cl-) levels were roughly equivalent in both maternal and fetal compartments. In umbilical arteries (UA), ALDO showed a definite relationship with 18OH-B and ACTH, however, did not for DOC, A-II, Na+ or K+. A comparison between umbilical vein (UV) and UA, revealed a relationship between ALDO, 18OH-B and PRA. Neonatal DOC, PRA, A-II and ACTH decreased significantly during the 1st post partum day in the presence of a rapid increase of 18OH-B and ALDO to levels in excess of that found in UA, these conditions persist up to the 3rd post partum day. Neonates with birth weights of less than 2.5 kg showed high ALDO, PRA, A-II ad K+ levels in the umbilical plasma, especially the UA. Comparing these neonates with those exceeding 3.0 kg birth weight revealed that in the UA, ALDO and K+ were at high levels. Neonatal PRA, A-II, Na+ and K+ showed no demonstrable variations up to the 8th post partum day and DOC after day 1 increased in the presence of a decrease in ALDO levels during day 1 and 18OH-B during day 3. Comparison of findings between the R-A-ALDO, water and electrolyte balance in fetuses and neonates are discussed.