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Arginine vasopressin (AVP) related water resorption in the collecting duct acts through aquaporins 2 specific water channels. AQP2 are small integral tetrameric plasma membrane proteins. Each of four subunits is selectively permeable to water. In mammals lack of vasopressin stimulation causes AQP2 storage in intracellular vesicles of the principal cells of the renal distal tubule and collecting duct. AVP acts through specific V receptors. Arginine vasopressin receptor binding increases intracellular production of cAMP and increases protein kinase A (PKA) activity. Ser256, Ser261, Ser264 and Ser269 are phosphorylated in the cytoplasmic C-terminal region of AQP2 by active PKA. Phosphorylation of at least three AQP2 monomers in each tetramer is required to start AQP2 translocation from intracellular vesicles and to cause their fusion with the apical membrane. Kidneys of animals and human neonates show a lot of morphological and functional differences. Adaptation, growth and maturation processes may be accompanied by escalation of diseases. Especially water-electrolyte imbalance can occur as a result of renal and extrarenal loss of water and electrolytes. Kidney immaturity after birth (renal narrow functional reserve and limited ability to excrete concentrated urine) favors this kind of disorders. Reduced ability to form osmotic gradient in kidney medulla as well as less efficient kidney response to vasopressin with AQP2
may cause lower capacity to save water in neonate kidneys. Role of this aquaporin in water tubular resorption in neonate is not explained but it may play the key role in this process. The renal tubular AQP2 expression in neonates is about 50% lower than in adults. In addition lower expression of V receptors in newborn kidneys causes reduced response to AVP. Higher levels of PGE , lesser levels of cAMP and restricted PKAa production are also observed in neonates. Moreover in neonates in comparison to adults renal AQP2 excretion do not correlate strictly with AVP concentration.

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The Editorial Board
Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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