Neonatal kidney, fluids, and electrolytes.

Numerous clinical studies during the past two decades have indicated that kidney function and regulation of electrolyte and fluid balance undergo profound changes in the neonatal period. The genetic mechanisms behind these developmental changes have recently been the topic for many investigations and has led to the identification of factors, reviewed here, that seem to be of extraordinary importance for the induction of kidney differentiation and maturation. For a long time it has been debated whether immaturity of renal function might have any clinical consequences. It now seems clear that at least one aspect of renal immaturity, namely the high urinary sodium excretion in preterm infants, which often results in negative sodium balance, should be paid more attention to because it might interfere with growth. Two recent review articles discuss this issue. The profound changes in fluid and electrolyte homeostasis that occur in the neonatal period, involves most tissues. This is exemplified with some recent exciting studies on the changes in ion transport that occur in the lung around birth.